1N Cell Biology PDF

Lecture Structure: Part 1: Eukaryotic and Prokaryotic Cells 1. Eukaryotic Cells: ○ Definition: Complex cells with a defined nucleus and membrane-bound organelles. ○ Key Components: Organelles: Such as the nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus. Membranes: Play a crucial role in compartmentalization and transport of molecules within the cell (detailed transport mechanisms will be covered in Lecture 2). 2. Prokaryotic Cells: ○ Definition: Simpler cells that lack a true nucleus and membrane-bound organelles. ○ Structure and Differences: No true nucleus; DNA is free-floating in the cytoplasm (nucleoid region). Examples include bacteria and archaea. ○ Comparison: Differences in size, complexity, and organelle presence when compared to eukaryotic cells. Part 2: The Cell Cycle, Meiosis, and Differentiation 1. The Cell Cycle: ○ Phases: The cell cycle involves stages like interphase (G1, S, G2) and mitosis. ○ Mitosis: Division of a eukaryotic cell into two identical daughter cells. 2. Meiosis: ○ Process: Reduces the chromosome number by half, producing four non-identical gametes (sperm or egg cells). ○ Importance: Essential for sexual reproduction and genetic diversity. 3. Cell Differentiation: ○ Definition: The process by which unspecialized cells become specialized in structure and function. ○ Significance: Key to the development of multicellular organisms. Learning Outcomes: Understanding Eukaryotic Organelles: Familiarize with the names, structures, and functions of organelles like the nucleus, mitochondria, ribosomes, and more. Cellular Compartments: Understand the role of membranes in compartmentalizing and managing cellular functions. Key Differences Between Prokaryotic and Eukaryotic Cells: Develop a clear understanding of their structural and functional differences. Introduction to the Cell Cycle: Grasp the stages of cell division (mitosis and meiosis) and their significance in growth and reproduction. == Learning Outcomes - Part 1: Eukaryotic and Prokaryotic Cells 1. Know the names and functions of some eukaryotic organelles and cell junctions: ○ Be able to identify key organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, etc. ○ Understand the roles these organelles play in cellular functions like energy production, protein synthesis, and waste disposal. ○ Cell junctions: Learn about the different types of cell junctions (e.g., tight junctions, desmosomes, gap junctions) and their roles in maintaining the integrity of tissues and enabling communication between cells. 2. Understand the key differences between eukaryotic and prokaryotic organisms: ○ Eukaryotes: Organisms whose cells have a defined nucleus and membrane-bound organelles (e.g., plants, animals, fungi). ○ Prokaryotes: Organisms that lack a true nucleus and organelles (e.g., bacteria, archaea). ○ Differences include: Presence of a nucleus in eukaryotes vs. nucleoid region in prokaryotes. Eukaryotic cells are generally larger and more complex. Prokaryotes reproduce asexually through binary fission, while eukaryotes undergo mitosis and meiosis. 3. Know what a virus is: ○ Viruses are acellular entities that are neither prokaryotic nor eukaryotic. ○ They require a host to replicate and consist of genetic material (DNA or RNA) encased in a protein coat (capsid). ○ They can infect both prokaryotic and eukaryotic cells, leading to diseases in humans, animals, and plants. == Eukaryotic Cell Structure The term "eukaryotic" comes from ancient Greek, where "eu" means true and "karyote" means kernel or nucleus. This indicates that eukaryotic cells have a true nucleus, which is membrane-bound, unlike prokaryotic cells. Key Features of Eukaryotic Cells: 1. Linear DNA Contained Within the Nucleus: ○ Eukaryotic cells have linear DNA organized into chromosomes. This DNA is stored in the nucleus, which is enclosed by a nuclear membrane. ○In contrast, prokaryotic cells (such as bacteria) have circular DNA and lack a true nucleus. 2. Membrane-Bound Organelles: ○ Eukaryotic cells contain various organelles (specialized structures within the cell), each of which is surrounded by its own membrane. These organelles carry out specific functions necessary for the cell's survival. Examples of Eukaryotic Organelles: Nucleus: The control center of the cell, housing the cell's DNA and controlling its activities. Mitochondria: Known as the powerhouse of the cell, it generates energy (ATP) through cellular respiration. Chloroplasts (in plants): Responsible for photosynthesis, converting light energy into chemical energy. Endoplasmic Reticulum (ER): Plays a role in protein and lipid synthesis. The rough ER is studded with ribosomes for protein synthesis, while the smooth ER is involved in lipid production. Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for storage or transport out of the cell. Lysosomes: Contain enzymes that break down waste materials and cellular debris. These features distinguish eukaryotic cells from prokaryotic cells, which lack these membrane-bound organelles and have simpler structures. == Eukaryotic Cell Structure The term "eukaryotic" comes from ancient Greek, where "eu" means true and "karyote" means kernel. Eukaryotic cells are characterized by a true nucleus that contains linear DNA and several membrane-bound organelles that perform specialized functions. Key Features of Eukaryotic Cells: 1. Linear DNA Contained Within the Nucleus: ○ Eukaryotic cells store their DNA inside the nucleus, which is enclosed by a nuclear membrane. The DNA is linear, unlike the circular DNA found in prokaryotes. 2. Membrane-Bound Organelles: ○ Nucleus: The control center of the cell, containing DNA. ○ Plasma Membrane: The outermost layer of animal cells, controlling the movement of substances in and out of the cell. In plant cells, a cell wall exists outside the plasma membrane for extra support. ○ Mitochondria: Known as the powerhouse of the cell, generating energy (ATP). ○ Vesicles: Small sacs that transport materials like proteins within the cell. They ensure that materials are delivered to the correct organelles, preventing errors like delivering liver-specific proteins to the pancreas. ○ Golgi Body: A processing and packaging unit where proteins are modified and packed into vesicles for transport. ○ Lysosomes and Peroxisomes: Small organelles involved in breaking down waste and detoxifying harmful substances. ○ Ribosomes: The protein production factories of the cell. These can be found either free-floating or attached to the rough endoplasmic reticulum (ER). ○ Endoplasmic Reticulum (ER): There are two types: Rough ER: Studded with ribosomes and involved in protein synthesis. Smooth ER: Lacks ribosomes and is involved in lipid synthesis and detoxification. Labelled Diagram: The labelled diagram of a eukaryotic cell will show the key structures mentioned above, including the nucleus, plasma membrane, mitochondria, vesicles, Golgi body, lysosomes, peroxisomes, ribosomes, and the rough and smooth ER. These components work together to maintain the cell's function and structure. This structure differentiates eukaryotic cells from prokaryotic cells, which lack membrane-bound organelles and have a simpler structure. == Eukaryotic Cell - Plasma Membrane The plasma membrane, also known as the cell membrane, is a critical structure of eukaryotic cells. Its main role is to serve as a barrier that separates the internal environment of the cell from the external environment, regulating what enters and exits the cell. Key Features: 1. Lipid Bilayer: ○ The plasma membrane is composed of a bilayer of lipids. "Bilayer" refers to the fact that there are two layers of lipid molecules. ○ The lipids are arranged with their hydrophilic heads (water-attracting) facing the outside and inside of the cell, while their hydrophobic tails (water-repelling) face each other in the middle. 2. Selectively Permeable: ○ The membrane is selectively permeable, meaning it controls which substances can pass through it. This property allows the cell to maintain its internal environment while regulating the exchange of materials like nutrients and waste. ○ It allows essential substances like oxygen, glucose, and ions to enter, while waste products are expelled. 3. Proteins in the Plasma Membrane: ○ Intrinsic (Integral) Proteins: These proteins span the entire membrane and are involved in transport across the membrane. ○ Extrinsic (Peripheral) Proteins: These proteins are attached to one side of the membrane and play a role in signaling or maintaining the structure of the membrane. 4. Functions of the Plasma Membrane: ○ Protection: It provides a barrier that protects the internal contents of the cell from the external environment. ○ Exchange: It allows selective exchange of substances. For example, it helps cells take in necessary ions (e.g., magnesium) and get rid of excess substances like potassium. == Eukaryotic Cell - Nucleus The nucleus is a central and defining feature of eukaryotic cells. It contains the genetic material and regulates many activities of the cell, including gene expression and cell division. Key Features: 1. Chromosomes (Protein-bound, Linear DNA): ○ The nucleus contains chromosomes, which are structures made up of linear DNA bound to proteins (mainly histones). This DNA carries the genetic information necessary for the cell's function and reproduction. 2. Nucleoli: ○ Inside the nucleus, one or more nucleoli are present. Their main function is to produce and assemble ribosomes, which are essential for protein synthesis. Ribosomes are assembled in the nucleolus and then exported to the cytoplasm where they perform their function. 3. Nuclear Envelope: ○ The nuclear envelope is a double membrane that encloses the nucleus, separating it from the cytoplasm. Each layer of the envelope is a phospholipid bilayer, similar to the plasma membrane. The nuclear envelope regulates the passage of molecules in and out of the nucleus, maintaining its environment. 4. Nuclear Lamina: ○ The nuclear lamina is a dense fibrillar network of proteins just beneath the inner membrane of the nuclear envelope. It provides structural support to the nucleus, helping it maintain its shape and organize the chromatin. 5. Nuclear Pores: ○ The nuclear envelope is perforated by nuclear pores, which are channels that allow the transport of molecules, such as RNA and proteins, between the nucleus and the cytoplasm. These pores are essential for regulating the exchange of materials necessary for gene expression and cell growth. 6. Nucleoplasm: ○ The interior of the nucleus is filled with nucleoplasm, a gel-like substance that contains the chromatin (DNA and proteins) and the nucleolus. It provides the medium for the processes occurring within the nucleus. The nucleus is vital for regulating cellular activities, such as gene expression and protein synthesis, which are critical for cellular function, growth, and response to environmental signals. The nucleolus, in particular, plays a central role in ribosome production, which ultimately drives protein synthesis in the cytoplasm. == Eukaryotic Cell - Ribosomes Ribosomes are essential cellular organelles responsible for protein synthesis. They translate genetic information from mRNA to form proteins, a process crucial for cell function and survival. Key Features: 1. Large Protein/RNA Complexes: ○ Ribosomes are composed of ribosomal RNA (rRNA) and proteins. They exist in two subunits: a large and a small subunit. These two parts remain separate until protein synthesis begins. 2. Located in the Cytosol: ○ Ribosomes can be found floating freely in the cytosol or attached to the endoplasmic reticulum (ER) in eukaryotic cells, specifically forming the rough ER. 3. Translation of mRNA: ○ The main function of ribosomes is to "read" messenger RNA (mRNA) and translate the genetic code into proteins. This process, called translation, involves the ribosome moving along the mRNA strand and assembling amino acids into a polypeptide chain. 4. Association with Endoplasmic Reticulum (ER): ○ Ribosomes can attach to the rough endoplasmic reticulum (RER) in eukaryotic cells. This allows the newly synthesized proteins to be directly inserted into the ER for further modification or transport. In prokaryotic cells, ribosomes may attach to the plasma membrane as they lack membrane-bound organelles. Protein Production Process: 1. Transcription: ○ The process of protein production begins with transcription inside the nucleus. DNA is transcribed into messenger RNA (mRNA), which carries the genetic code out of the nucleus via nuclear pores into the cytoplasm. 2. Translation: ○ Once in the cytoplasm, ribosomes bind to the mRNA. During translation, the ribosome reads the genetic sequence and assembles a chain of amino acids to form a protein. This process involves two ribosomal subunits coming together to facilitate translation. 3. Formation of Polypeptide Chains: ○ As the ribosome moves along the mRNA, it facilitates the attachment of amino acids into a growing polypeptide chain. This chain eventually folds into a functional protein. Importance of Ribosomes: Ribosomes are crucial for producing the proteins that perform a wide range of functions in the cell, from structural components to enzymes, hormones, and antibodies. Without ribosomes, cells would be unable to produce the proteins necessary for their function and survival. == Eukaryotic Cell - Smooth Endoplasmic Reticulum (SER) The Smooth Endoplasmic Reticulum (SER) is an essential organelle in eukaryotic cells, involved in various functions depending on the type of cell in which it resides. Key Features: 1. Lipid Processing and Secretion: ○ One of the primary roles of the SER is the synthesis and processing of lipids. It produces phospholipids, cholesterol, and other lipid molecules necessary for the maintenance of cell membranes and for secretion outside the cell. 2. Lipid Secretion: ○ In certain cells, the SER is involved in the secretion of lipids and lipoproteins, which are essential for various biological functions. 3. Absence of Ribosomes: ○ Unlike the Rough Endoplasmic Reticulum (RER), which has ribosomes attached to its surface, the SER lacks ribosomes, giving it a smooth appearance under a microscope. This difference in structure leads to distinct functions between the two types of endoplasmic reticulum. Cell-Specific Functions: 1. Hormone Synthesis (Endocrine Glands): ○ In endocrine glands like the adrenal glands, the SER plays a key role in the synthesis of steroid hormones. These hormones include cortisol, aldosterone, and sex steroids (e.g., testosterone and estrogen), all crucial for regulating metabolism, stress response, and reproductive functions. 2. Detoxification (Liver Cells): ○ In liver cells, the SER catalyzes reactions that help detoxify harmful substances, including drugs, metabolic waste, and toxins. The SER modifies these substances to make them water-soluble, which allows them to be more easily excreted from the body. ○ For example, when you take a medication like paracetamol, the liver's SER helps detoxify it, converting harmful byproducts into less toxic substances for safe removal from the body. 3. Calcium Storage and Release: ○ In muscle cells, the SER acts as a storage site for calcium ions. The controlled release of calcium from the SER triggers muscle contraction. Importance of the SER: The Smooth Endoplasmic Reticulum is vital for the synthesis and processing of lipids, hormone production, detoxification, and calcium regulation. Its function varies depending on the cell type, highlighting its adaptability and importance in maintaining cellular homeostasis. In summary, the SER is a multifunctional organelle, playing crucial roles in lipid metabolism, detoxification, hormone production, and calcium storage, depending on the specific needs of the cell. == Eukaryotic Cell - Rough Endoplasmic Reticulum (RER) The Rough Endoplasmic Reticulum (RER) is a key organelle involved in protein synthesis and processing, characterized by its surface, which is studded with ribosomes, giving it a "rough" appearance. Key Features: 1. Studded with Ribosomes: ○ The defining feature of the RER is the presence of ribosomes attached to its outer surface. These ribosomes play a crucial role in translating messenger RNA (mRNA) into proteins. 2. Protein Production: ○ The RER is primarily responsible for the synthesis of two types of proteins: Membrane Proteins: Proteins that are integrated into or associated with the cell membrane. Extracellular Proteins: Proteins that are secreted out of the cell, such as enzymes, hormones, and antibodies. 3. Secretory Pathway: ○ After synthesis, proteins are processed in the RER and packaged into vesicles. These vesicles transport the proteins through the secretory pathway, where they may move to the Golgi apparatus for further modification and sorting, and eventually be directed to their final destination (e.g., cell membrane or secretion outside the cell). Functions: 1. Protein Synthesis: ○ The ribosomes on the RER translate mRNA into polypeptide chains, which are then processed and folded into functional 3D protein structures. 2. Protein Folding and Modification: ○ As proteins are synthesized, they are folded into their correct shapes and may undergo post-translational modifications such as glycosylation (adding sugar molecules), helping them to become fully functional. 3. Transport of Proteins: ○ The RER plays a central role in packaging newly synthesized proteins into vesicles, which are transported to the Golgi apparatus for further processing or directly to other cellular locations, such as the plasma membrane or lysosomes. 4. Production of Secretory and Membrane Proteins: ○ The RER produces proteins destined for: The cell membrane: Integral membrane proteins are crucial for various cellular processes like transport and signal transduction. Extracellular secretion: Many proteins synthesized by the RER are secreted by the cell to function in extracellular spaces, such as digestive enzymes and signaling molecules. Summary: The Rough Endoplasmic Reticulum plays a critical role in protein production, folding, and trafficking within the cell. Its primary function is the synthesis of membrane-bound and secretory proteins, which are processed in the RER before being sent to their final destination via the secretory pathway. == Eukaryotic Cell - Origins of the Nucleus and Endoplasmic Reticulum (ER) The autogenous model explains the origin of the nucleus and endoplasmic reticulum (ER) in eukaryotic cells as a result of internal evolution from the plasma membrane of a primitive cell. Autogenous Model: The autogenous model posits that the nucleus and ER evolved from invaginations (inward folding) of the plasma membrane in an ancient prokaryotic ancestor. Over time, this membrane gradually enclosed the genetic material, forming what we recognize today as the nucleus. Process: 1. Initial State: ○ In primitive cells, genetic material (DNA) was free-floating in the cytoplasm, as seen in modern-day prokaryotes. 2. Membrane Invagination: ○ Due to evolutionary pressures or unknown factors, the plasma membrane began folding inward toward the genetic material. ○ As this membrane continued to invaginate, it eventually surrounded the DNA, creating an enclosed nuclear membrane and forming a nucleus. 3. Formation of the ER: ○ As the plasma membrane folded inwards to form the nucleus, it also gave rise to the endoplasmic reticulum. ○ The endoplasmic reticulum (both smooth and rough) is closely associated with the nucleus, with the rough ER being directly attached to the nuclear envelope. Key Structures: Nucleus: ○ Enclosed genetic material in a double membrane, protecting it and regulating the exchange of materials via nuclear pores. Endoplasmic Reticulum: ○ Located next to the nucleus and derived from the same membrane invagination. It includes: Rough ER: Studded with ribosomes for protein synthesis. Smooth ER: Involved in lipid synthesis and detoxification processes. Summary: The autogenous model explains the origin of the nucleus and ER as a result of the plasma membrane folding inwards to surround the genetic material, creating a compartmentalized structure. This allowed for more complex functions and marked a key step in the evolution of eukaryotic cells. == Eukaryotic Cell - Golgi Apparatus The Golgi apparatus, also known as the Golgi body, Golgi complex, plays a crucial role in the secretory pathway of eukaryotic cells. Here are its key functions and features: Functions of the Golgi Apparatus: 1. Exit Route from the ER: ○ Proteins and lipids synthesized in the endoplasmic reticulum (ER) are transported to the Golgi apparatus. ○ The Golgi processes these molecules and packages them into vesicles for transport to their final destinations. 2. Carbohydrate and Polysaccharide Synthesis: ○ The Golgi apparatus is involved in synthesizing various carbohydrates and polysaccharides. ○ This includes the creation of complex sugars that are added to proteins and lipids. 3. Protein Glycosylation: ○ Glycosylation is the process where sugars are added to proteins. This modification can affect protein folding, stability, and function. ○ The Golgi modifies proteins by adding carbohydrate groups, resulting in glycoproteins. 4. Protein Sorting: ○ The Golgi apparatus sorts and packages proteins and lipids into vesicles that are then directed to their appropriate destinations, such as the cell membrane, lysosomes, or secretion outside the cell. 5. Glycosaminoglycans (GAGs) Synthesis: ○ The Golgi synthesizes glycosaminoglycans (GAGs), which are long, unbranched polysaccharides. ○ GAGs are essential components of the extracellular matrix and contribute to various cellular functions. Structure: Flattened Membrane Stacks: ○ The Golgi apparatus is composed of a series of flattened, membrane-bound sacs called cisternae. ○ These stacks process and modify molecules as they pass through the Golgi. Processing and Packaging: ○ As proteins and lipids move through the Golgi stacks, they undergo various modifications, including glycosylation. ○ Modified molecules are then packaged into vesicles for transport to their target locations. Additional Information: Proteins synthesized in the rough ER are sent to the Golgi for further processing. The Golgi modifies these proteins and lipids, ensuring they are correctly folded and functional before transport. Glycosaminoglycans (GAGs) are important for maintaining cell structure and function. Their dysfunction can lead to diseases, which will be discussed in detail in later lectures. Summary: The Golgi apparatus acts as the cell's post-office, processing, modifying, and packaging proteins and lipids received from the ER. It plays a vital role in ensuring that molecules are properly modified and delivered to their correct locations within or outside the cell. == Eukaryotic Cell - Lysosomes Lysosomes are membrane-bound organelles crucial for maintaining cellular health and function. They play a key role in the degradation and recycling of cellular materials and external invaders. Functions of Lysosomes: 1. Intracellular Digestion: ○ Lysosomes contain about 50 different hydrolytic enzymes capable of breaking down various biomolecules. ○ These enzymes include nucleases (to degrade DNA and RNA), proteases (to break down proteins), and glycosidases (to digest carbohydrates and glycogen). 2. Degradation of Cellular Components: ○ Lysosomes break down excess or worn-out cell parts, such as damaged organelles, through a process called autophagy. ○ This helps in recycling cellular components and maintaining cell health. 3. Destruction of Pathogens: ○ Lysosomes also destroy invading viruses, bacteria, and other pathogens. ○ For example, they play a critical role in the immune response by breaking down harmful microorganisms. 4. Maintenance of Acidic Environment: ○ Lysosomes operate optimally at an acidic pH (around 4.5 to 5.0). ○ The acidic environment is essential for the activity of their digestive enzymes. Outside the lysosome, at a neutral pH (7.2), these enzymes are inactive, preventing unintended cellular damage. 5. Prevention of Cellular Damage: ○ The lysosomal membrane protects the rest of the cell from the potentially harmful effects of the digestive enzymes. ○ If a lysosome were to burst, its enzymes would not be active outside the acidic environment, thus preventing widespread damage. Structure: Membrane-Bound Organelles: ○ Lysosomes are surrounded by a single lipid bilayer membrane. ○ This membrane maintains the acidic internal environment and contains the hydrolytic enzymes. Enzymatic Content: ○ They house various digestive enzymes necessary for breaking down different types of biological macromolecules. Summary: Lysosomes are essential for cellular homeostasis, playing a vital role in digesting and recycling cellular components and destroying harmful pathogens. Their ability to function effectively in an acidic environment ensures that they carry out their destructive tasks without harming the rest of the cell. This compartmentalization of functions illustrates the complexity and efficiency of cellular organization, highlighting how different organelles work in harmony to maintain cell health and function. == Eukaryotic Cell - Peroxisomes Peroxisomes are membrane-bound organelles involved in various oxidative reactions within the cell. They play a crucial role in maintaining cellular health by handling oxidative stress and producing essential biomolecules. Functions of Peroxisomes: 1. Oxidation Reactions: ○ Enzymatic Activity: Peroxisomes contain around 50 different enzymes that perform oxidation reactions. ○ Hydrogen Peroxide Production: Many of these reactions produce hydrogen peroxide (H₂O₂), a reactive oxygen species. 2. Hydrogen Peroxide Degradation: ○ Catalase: Peroxisomes house an enzyme called catalase, which decomposes hydrogen peroxide into water (H₂O) and oxygen (O₂). Reaction: 2H2O2→2H2O+O22H₂O₂ \rightarrow 2H₂O + O₂2H2O2→2H2O+O2 ○ Purpose: This reaction helps neutralize the potentially harmful effects of hydrogen peroxide, protecting cellular components from oxidative damage. 3. Formation of Plasmalogens: ○ Plasmalogens: Peroxisomes are involved in the synthesis of plasmalogens, a class of phospholipids. ○ Function: Plasmalogens are essential components of myelin, the protective sheath surrounding nerve cells. They are the most abundant class of phospholipids in myelin. Role in Oxidative Stress: Oxidative Stress: Free radicals, which are molecules with unpaired electrons, can damage cellular components like DNA, proteins, and lipids. This damage is known as oxidative stress. Antioxidants: To counteract oxidative stress, cells rely on antioxidants, which have extra electrons that neutralize free radicals by donating an electron. Peroxisomal Function: By breaking down hydrogen peroxide, peroxisomes help reduce oxidative stress and maintain a balance between free radicals and antioxidants. Summary: Peroxisomes are vital for cellular health due to their role in oxidative reactions and detoxification. They produce hydrogen peroxide but also contain enzymes like catalase to safely convert it into harmless water and oxygen. Additionally, they contribute to the formation of plasmalogens, crucial for myelin formation and overall cellular function. Through these processes, peroxisomes help manage oxidative stress and protect the cell from damage caused by free radicals. == Eukaryotic Cell - Mitochondria Mitochondria are essential double-membraned organelles found in both plant and animal cells. They are often referred to as the "powerhouses" of the cell due to their role in energy production. Here’s a comprehensive look at their structure and functions: Structure of Mitochondria: Outer Membrane: The outer boundary of the mitochondrion, which is smooth and permeable to small molecules and ions. Inner Membrane: Folded into structures called cristae, this membrane is where many biochemical reactions occur. The folds increase the surface area available for reactions. Matrix: The space inside the inner membrane, where the tricarboxylic acid (TCA) cycle and other metabolic processes occur. Functions of Mitochondria: 1. ATP Production: ○ Cellular Respiration: Mitochondria are the site of cellular respiration, where glucose and fatty acids are converted into ATP (adenosine triphosphate), the cell’s main energy currency. ○ Electron Transport Chain: Located in the inner membrane, this chain is crucial for ATP production through oxidative phosphorylation. 2. Fatty Acid β-Oxidation: ○ This process, occurring in the mitochondria, breaks down fatty acids to generate acetyl-CoA, which then enters the TCA cycle for ATP production. 3. Tricarboxylic Acid (TCA) Cycle: ○ Also known as the Krebs cycle or citric acid cycle, this cycle occurs in the mitochondrial matrix and is pivotal for generating energy through the oxidation of acetyl-CoA. 4. Calcium Regulation: ○ Mitochondria help regulate intracellular calcium levels, which is important for various cellular processes, including muscle contraction and neurotransmitter release. 5. Cell Apoptosis: ○ Mitochondria play a role in programmed cell death (apoptosis). They release factors that activate apoptosis pathways when a cell is damaged or no longer needed. 6. Genetic Material: ○ Mitochondrial DNA: Mitochondria have their own circular DNA, distinct from nuclear DNA. This allows them to produce some of their own proteins and replicate independently of the cell. ○ Ribosomes: Mitochondria contain their own ribosomes, which are involved in synthesizing mitochondrial proteins. Summary: Mitochondria are crucial for energy production, cellular metabolism, and maintaining cellular health. They are characterized by their double membrane structure, with the inner membrane being highly folded to maximize energy production efficiency. In addition to generating ATP, mitochondria are involved in fatty acid metabolism, calcium regulation, and apoptosis. Their own DNA and ribosomes enable them to manage some of their own functions and replicate independently within the cell. == Eukaryotic Cell - Mitochondria Symbiotic Theory of Mitochondrial Origin: The origin of mitochondria is explained by the endosymbiotic theory, which proposes that mitochondria originated from a symbiotic relationship between early eukaryotic cells and certain bacteria. Here's an overview of this theory: Endosymbiotic Theory: 1. Early Eukaryotic Cell: ○ According to this theory, primitive eukaryotic cells, which lacked mitochondria, engulfed aerobic bacteria (bacteria that use oxygen for respiration). 2. Formation of Symbiosis: ○ Instead of digesting these bacteria, the early eukaryotic cell formed a mutualistic relationship with them. The bacteria were surrounded by a double membrane, which eventually evolved into the mitochondrion. 3. Evolution Over Time: ○ Over billions of years, these engulfed bacteria became integral parts of the host cell. They evolved into mitochondria, providing several benefits to the host cell, such as enhanced energy production through aerobic respiration. 4. Mutual Benefits: ○ Bacteria: The engulfed bacteria received a protected environment and nutrients from the host cell. ○ Eukaryotic Cell: The host cell benefited from the bacteria's ability to produce ATP more efficiently through oxidative phosphorylation, which was crucial for the cell's energy needs. 5. Symbiotic Relationship: ○ This relationship is termed symbiotic because both organisms benefited from living together. The bacteria (now mitochondria) adapted to their new environment and became specialized for energy production, while the host cell gained a significant advantage in ATP production. 6. Genetic Evidence: ○ Modern mitochondria still retain their own circular DNA, similar to bacterial DNA, and their own ribosomes. This supports the theory that mitochondria originated from free-living bacteria. 7. Biochemical Evidence: ○ Mitochondria share several similarities with certain bacteria, such as their size, shape, and the fact that they replicate similarly to bacteria. Summary: The endosymbiotic theory suggests that mitochondria originated from a symbiotic relationship between an ancestral eukaryotic cell and aerobic bacteria. This mutualistic relationship led to the bacteria evolving into mitochondria, which provided the host cell with enhanced energy production capabilities. Over time, the bacteria became an integral part of the eukaryotic cell, leading to the complex mitochondria we see today. == Eukaryotic Cell - Cell-Cell Junctions Cell-cell junctions are specialized structures that allow cells to adhere to each other, communicate, and coordinate functions within tissues. Here’s a summary of the main types of cell-cell junctions: 1. Tight Junctions Function: Seal gaps between adjacent epithelial cells to prevent leakage of extracellular fluid. Structure: Form a continuous belt-like structure around the cell perimeter. Proteins Involved: Claudins and occludins. Characteristics: Very tight, preventing passage of molecules between cells, which maintains the integrity of the epithelial barrier. 2. Adherens Junctions Function: Connect actin filament bundles in one cell to those in an adjacent cell, providing mechanical strength and structural support. Structure: Often found in a belt-like formation just beneath tight junctions. Proteins Involved: Cadherins (adherens junctions) and catenins. Characteristics: Allows cells to adhere strongly to one another and maintain tissue structure. 3. Desmosomes Function: Provide strong adhesion between cells, particularly in tissues subject to mechanical stress. Structure: Link intermediate filaments in one cell to those in a neighboring cell, creating a sturdy network. Proteins Involved: Desmogleins and desmocollins (cadherin family proteins), linked to intermediate filaments. Characteristics: Strong adhesion, crucial in tissues like cardiac muscle and epidermis, which undergo constant mechanical stress. 4. Gap Junctions Function: Allow the passage of small water-soluble molecules and ions between adjacent cells, facilitating cell-to-cell communication. Structure: Consist of connexins that form a connexon (hemichannel) in each cell, aligning with connexons in adjacent cells to form a channel. Characteristics: Enable direct transfer of small molecules, ions, and electrical signals, which is essential for synchronized activity in tissues like the heart. Junctional Complex: Overview: The junctional complex refers to the network of tight junctions, adherens junctions, and desmosomes that work together to maintain cell adhesion, tissue integrity, and communication. Components: Typically found in epithelial tissues, where these junctions are crucial for forming barriers, providing structural support, and allowing communication between cells. Summary: Tight Junctions: Prevent leakage between cells. Adherens Junctions: Connect actin filaments and provide structural support. Desmosomes: Offer strong adhesion and withstand mechanical stress. Gap Junctions: Facilitate communication through small molecule passage. These junctions play essential roles in maintaining the structure and function of tissues by ensuring that cells adhere to one another properly and communicate effectively. == Eukaryotic Cell - Cell-Matrix Anchoring Junctions Cell-matrix anchoring junctions are structures that connect cells to the extracellular matrix (ECM), providing mechanical support and stability. These junctions are crucial for maintaining tissue integrity and facilitating cell signaling. 1. Actin-Linked Cell–Matrix Junctions Function: Anchor actin filaments in the cell to the extracellular matrix. Structure: Involves integrins that bind to ECM components such as collagen and fibronectin. These integrins link to actin filaments inside the cell through adaptor proteins like talin and vinculin. Characteristics: Provides strong mechanical attachment and helps cells to adhere firmly to the ECM. This connection helps in maintaining cell shape and stability. 2. Hemidesmosomes Function: Anchor intermediate filaments in the cell to the extracellular matrix. Structure: Consists of integrins (such as α6β4 integrin) that bind to ECM components like laminin. The integrins are connected to intermediate filaments inside the cell via plakins like plectin. Characteristics: Provides robust attachment of cells to the basement membrane. This anchorage is particularly important in tissues subject to mechanical stress, such as the epithelial layer of the skin. Summary of Cell-Matrix Anchoring Junctions: Actin-Linked Cell-Matrix Junctions: ○ Anchored Filament: Actin filaments. ○ Components: Integrins, talin, vinculin. ○ Function: Strengthen adhesion and maintain cell shape. Hemidesmosomes: ○ Anchored Filament: Intermediate filaments. ○ Components: Integrins, laminin, plakins (e.g., plectin). ○ Function: Securely anchor cells to the basement membrane, providing structural stability in stress-bearing tissues. == The Living World - Three Major Domains The classification of life into three major domains—Bacteria, Archaea, and Eukaryotes—reflects fundamental differences in cellular structure and function. Here’s an overview of these domains: 1. Prokaryotes Prokaryotes include both Bacteria and Archaea. These organisms are characterized by: Lack of a Membrane-Bound Nucleus: Their genetic material is not enclosed in a membrane-bound nucleus. Instead, it is found in a region called the nucleoid. Circular DNA: Their DNA is typically circular and not organized into chromosomes like in eukaryotes. Lack of Membrane-Bound Organelles: They do not have membrane-bound organelles like mitochondria or endoplasmic reticulum. Bacteria Characteristics: Bacteria are unicellular organisms that can be found in almost every environment on Earth, including extreme environments. They can be beneficial (e.g., gut flora) or pathogenic (e.g., causing diseases). Structure: Bacteria have a cell wall composed of peptidoglycan. They may also have structures such as flagella for movement and pili for attachment. Archaea Characteristics: Archaea are also unicellular and often live in extreme environments, such as hot springs, salt lakes, and deep-sea hydrothermal vents. Unlike bacteria, archaea do not have peptidoglycan in their cell walls. Structure: They have unique lipids in their cell membranes and often have different ribosomal RNA sequences compared to bacteria. 2. Eukaryotes Characteristics: Eukaryotic cells have a membrane-bound nucleus that contains their genetic material. Their DNA is linear and organized into chromosomes. They also have various membrane-bound organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus. Types: Eukaryotes are classified into several kingdoms, including Protista, Fungi, Plantae, and Animalia. They include a wide variety of organisms, from single-celled protists to complex multicellular plants and animals. Key Differences: Nucleus: ○ Prokaryotes: No membrane-bound nucleus. ○ Eukaryotes: Membrane-bound nucleus. DNA: ○ Prokaryotes: Circular DNA. ○ Eukaryotes: Linear DNA organized into chromosomes. Organelles: ○ Prokaryotes: Lack membrane-bound organelles. ○ Eukaryotes: Contain membrane-bound organelles. Historical Context Carl Woese: In the 1970s, microbiologist Carl Woese revolutionized our understanding of prokaryotic classification by introducing the concept that prokaryotes are divided into two distinct domains—Bacteria and Archaea—based on differences in their ribosomal RNA sequences and other molecular characteristics. Interactions with Humans Archaea: Typically harmless and can be found in various environments, including the human body, where they often play neutral or beneficial roles. Bacteria: Can be either beneficial (e.g., gut microbiota) or harmful (e.g., pathogenic bacteria causing diseases). == Bacterial Cell - Features Cellular Comparison to Eukaryotes 1. Nucleus: ○ Bacteria: No membrane-bound nucleus. Genetic material is contained within the nucleoid region as a single, circular DNA molecule. ○ Eukaryotes: Membrane-bound nucleus containing linear DNA organized into chromosomes. 2. Cytoplasm: ○ Bacteria: Lacks membrane-bound organelles. The cytoplasm contains only ribosomes and other inclusions. ○ Eukaryotes: Contains membrane-bound organelles such as the endoplasmic reticulum, Golgi apparatus, mitochondria, etc. 3. Ribosomes: ○ Bacteria: Smaller ribosomes (70S) compared to eukaryotic ribosomes. 70S ribosomes are made up of a 50S large subunit and a 30S small subunit. ○ Eukaryotes: Larger ribosomes (80S) consisting of a 60S large subunit and a 40S small subunit. 4. Cell Wall: ○ Bacteria: Gram-Positive: Thick peptidoglycan cell wall. Retains the crystal violet stain used in Gram staining, appearing purple. Gram-Negative: Thin peptidoglycan layer with an outer membrane containing lipopolysaccharides. Does not retain crystal violet and appears pink/red after staining. ○ Eukaryotes: Plant cells have a cell wall made of cellulose; animal cells do not have a cell wall. 5. Outer Membrane: ○ Bacteria: Present in Gram-negative bacteria, forming a barrier to certain substances. ○ Eukaryotes: The outer membrane of eukaryotic cells is a plasma membrane with embedded proteins. Other Features of Bacterial Cells 1. Plasmid DNA: ○ Bacteria: Small, circular DNA molecules separate from chromosomal DNA. Plasmids often carry genes that confer advantages such as antibiotic resistance. ○ Eukaryotes: Plasmids are generally not present. Eukaryotic cells have linear DNA in chromosomes. 2. Capsule: ○ Bacteria: An outermost protective layer made of polysaccharides or proteins. Helps prevent dehydration and protects against the host's immune system. ○ Eukaryotes: No capsule; protection and structural support are provided by the cell wall (in plants) or the extracellular matrix (in animals). 3. Flagella: ○ Bacteria: Whip-like structures that provide motility. They can be single or multiple, and their structure and function differ from eukaryotic flagella. ○ Eukaryotes: Flagella are more complex and are made of microtubules arranged in a 9+2 arrangement. They also provide motility but have a different mechanism of movement. 4. Surface-Layer: ○ Bacteria: Sometimes have an additional surface-layer, such as an S-layer, which provides protection and adherence. ○ Eukaryotes: No surface-layer; instead, cells may have a plasma membrane with various surface proteins. Gram Staining Gram Positive: Cells have a thick peptidoglycan layer that retains the crystal violet stain, appearing purple. Gram Negative: Cells have a thin peptidoglycan layer and an outer membrane that does not retain the crystal violet stain but takes up the counterstain (usually safranin), appearing pink/red. Summary Prokaryotes (Bacteria and Archaea) are simpler in structure compared to eukaryotes and lack many of the organelles found in eukaryotic cells. Bacteria can be distinguished by their cell wall structure and staining properties, which is crucial for identifying and treating bacterial infections. == Bacterial Cell - Real-Life Features To visualize the structure of a bacterial cell as seen in real-life, it's useful to relate it to the diagrammatic representation: 1. Plasma Membrane: ○ Diagram: Represented as a thin layer surrounding the cell. ○ Real-Life: This is a lipid bilayer that controls the movement of substances into and out of the cell. It is selectively permeable and provides a barrier between the cell's interior and the external environment. 2. Capsule: ○ Diagram: Sometimes depicted as an outer layer surrounding the cell wall. ○ Real-Life: The capsule is a gelatinous layer outside the cell wall that offers protection against desiccation, phagocytosis, and helps in adherence to surfaces. It appears as a thick, protective layer in some bacteria. 3. Circular DNA: ○ Diagram: Shown as a single, circular strand located in the cytoplasm. ○ Real-Life: The circular DNA molecule (nucleoid) is located in the cytoplasm and contains the genetic information necessary for the cell’s functions and reproduction. 4. Flagellum: ○ Diagram: Illustrated as a long, whip-like structure. ○ Real-Life: The flagellum is a tail-like structure used for locomotion. It can be single or multiple, and its movement propels the bacterium through liquid environments. The flagellum is made of protein and is anchored in the cell membrane. 5. Plasmid DNA: ○ Diagram: Often represented as smaller circular DNA fragments. ○ Real-Life: Plasmids are extra-chromosomal DNA molecules that carry additional genetic information, often providing antibiotic resistance or other beneficial traits. 6. Surface-Layer: ○ Diagram: Sometimes included as an additional layer or S-layer. ○ Real-Life: This layer may be present in some bacteria, providing additional protection and aiding in adhesion to surfaces. Example of Real-Life Bacterial Structure Capsule: In bacteria like Streptococcus pneumoniae, the capsule is a key virulence factor that helps the bacteria evade the host's immune system. Flagellum: In Escherichia coli, flagella are used for motility in aqueous environments. == O Prokaryotic Cells - Ribosomes Ribosomes are essential for protein synthesis in all cells, but there are some key differences between prokaryotic and eukaryotic ribosomes: General Features of Ribosomes Structure: Ribosomes are large complexes of protein and RNA. Function: They "read" mRNA (messenger RNA) and synthesize proteins through a process called translation. Location: ○ Prokaryotic Cells: Ribosomes are found freely floating in the cytoplasm. ○ Eukaryotic Cells: Ribosomes can be free in the cytoplasm or attached to the endoplasmic reticulum (ER), forming the rough ER. Ribosome Size and Sedimentation Rate Prokaryotic Ribosomes: Known as 70S ribosomes. The "S" stands for Svedberg units, which is a measure of sedimentation rate, not weight. The 70S ribosome is composed of a small 30S subunit and a large 50S subunit. Eukaryotic Ribosomes: Known as 80S ribosomes, consisting of a small 40S subunit and a large 60S subunit. Note on Sedimentation Rate: The Svedberg unit (S) is a measure of how quickly a particle sediments during centrifugation, reflecting its size, shape, and density. It does not directly correspond to weight. Ribosome Function in Prokaryotes vs. Eukaryotes Prokaryotic Cells: ○ Location: Ribosomes are dispersed throughout the cytoplasm since prokaryotes lack membrane-bound organelles. ○ Function: Ribosomes in prokaryotes perform the same function as in eukaryotes—reading mRNA and synthesizing proteins. Eukaryotic Cells: ○ Location: Ribosomes are either free in the cytoplasm or attached to the endoplasmic reticulum (ER). The rough ER is so named because its ribosomes give it a "rough" appearance under the microscope. ○ Function: Similar to prokaryotic ribosomes, they synthesize proteins based on mRNA instructions. Visual Summary Prokaryotic Ribosomes: Smaller (70S), found free in the cytoplasm. Eukaryotic Ribosomes: Larger (80S), found free in the cytoplasm or attached to the ER. == Archaeal Cells - Features Archaea, often referred to as archaebacteria, share some similarities with bacteria but also have unique features that distinguish them: Cellular Features Nucleus: Like bacteria, archaea lack a true nucleus. Their DNA is circular and located in the cytoplasm. Membrane-Bound Organelles: Archaea, similar to bacteria, do not have membrane-bound organelles. Ribosomes: Archaea possess smaller ribosomes (70S), the same as bacteria. This is in contrast to the larger (80S) ribosomes found in eukaryotic cells. Extreme Environments: Many archaea are extremophiles, meaning they are adapted to survive in extreme conditions such as high temperatures, high salinity, or acidic environments. DNA Replication, RNA Transcription, and Translation: These processes in archaea are more similar to those in eukaryotes than in bacteria. This similarity extends to the machinery involved in these processes. Cell Membrane Composition: Archaeal cell membranes are composed of phospholipids with ether linkages, rather than the ester linkages found in bacterial and eukaryotic membranes. The phospholipids also have branched fatty acid chains. Function: The ether linkages and branched fatty acids provide stability and resilience, particularly in extreme environments. Cell Wall Composition: Archaea have cell walls made of pseudopeptidoglycan (also called pseudomurein) rather than true peptidoglycan found in bacterial cell walls. Structure: Pseudopeptidoglycan performs a similar protective function to peptidoglycan but differs in chemical structure. The term "pseudo" indicates that while it functions similarly, its structure is not identical to peptidoglycan. Genomes Complexity: Archaea genomes are generally larger and more complex than those of bacteria. This complexity includes more genes related to various cellular processes. Summary of Key Features No true nucleus; circular DNA Lack membrane-bound organelles Smaller (70S) ribosomes Adapted to extreme environments ("extremophiles") DNA replication, transcription, and translation processes similar to eukaryotes Cell membrane with ether linkages and branched fatty acids Cell wall made of pseudopeptidoglycan Larger and more complex genomes compared to bacteria == Three Major Domains of Life: Overview To understand the three major domains of life—Bacteria, Archaea, and Eukaryotes—it's important to grasp their similarities and differences. Here's a summary that captures the essential characteristics and distinctions among these domains: Bacteria Nucleus: No true nucleus; DNA is circular and located in the cytoplasm. Organelles: Lack membrane-bound organelles. Ribosomes: Smaller (70S) ribosomes. Cell Wall: Contains peptidoglycan (Gram-positive) or lacks peptidoglycan (Gram-negative). Membrane: Phospholipids with ester linkages. Habitat: Found in diverse environments, from soil to the human body. Example: Escherichia coli, Streptococcus. Archaea Nucleus: No true nucleus; DNA is circular and located in the cytoplasm. Organelles: Lack membrane-bound organelles. Ribosomes: Smaller (70S) ribosomes. Cell Wall: Contains pseudopeptidoglycan (not peptidoglycan). Membrane: Phospholipids with ether linkages and branched fatty acids. Habitat: Often found in extreme environments (extremophiles). Example: Methanogens, Halophiles. Eukaryotes Nucleus: True nucleus with linear DNA. Organelles: Have membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum). Ribosomes: Larger (80S) ribosomes, either free in the cytoplasm or attached to the endoplasmic reticulum. Cell Wall: Present in plants and fungi (cellulose in plants, chitin in fungi); absent in animal cells. Membrane: Phospholipids with ester linkages. Habitat: Found in diverse environments, including multicellular organisms. Example: Humans, Yeast, Plants. Summary of Similarities and Differences Similarities Bacteria and Archaea: Both lack a true nucleus and membrane-bound organelles. They have circular DNA and smaller (70S) ribosomes. Archaea and Eukaryotes: Both have similarities in DNA replication, RNA transcription, and translation processes, with archaea sharing more features with eukaryotes in these processes than with bacteria. Differences Cell Wall: Bacteria have peptidoglycan, archaea have pseudopeptidoglycan, and eukaryotes' cell walls (if present) have cellulose (plants) or chitin (fungi). Membrane Composition: Eukaryotic membranes have ester linkages in phospholipids, whereas archaeal membranes have ether linkages. Ribosome Size: Eukaryotes have 80S ribosomes, while bacteria and archaea have 70S ribosomes. == Viruses: Overview Characteristics of Viruses Non-living Particles: Viruses are considered non-living because they cannot carry out life processes on their own. Structure: ○ Genetic Material: Can be either DNA or RNA. ○ Capsid: A protein or lipid-protein coat that surrounds the genetic material. Replication: ○ Inside Host Cells: Viruses require a living host cell to replicate. They hijack the host cell's machinery to produce new virus particles. ○ Spread: Once new viruses are produced, they are released from the host cell, often causing the cell to burst, and then spread to infect new cells. Virus Life Cycle 1. Attachment: The virus attaches to a specific receptor on the surface of a host cell. 2. Entry: The virus or its genetic material enters the host cell. 3. Replication and Transcription: The virus uses the host cell's machinery to replicate its genetic material and transcribe it into viral proteins. 4. Assembly: New viral particles are assembled from the replicated genetic material and proteins. 5. Release: New viruses are released from the host cell, usually causing cell lysis (bursting) to spread and infect other cells. Examples and Impact COVID-19: The SARS-CoV-2 virus, responsible for COVID-19, exemplifies how viruses replicate inside host cells and cause illness. Flu: Influenza viruses also follow a similar replication process and cause seasonal flu. Controversy in Definition Living vs. Non-living: The debate continues over whether viruses should be classified as living or non-living because they cannot reproduce independently and lack cellular structures. Importance in Understanding Understanding how viruses work is crucial for developing treatments, vaccines, and preventive measures. This knowledge helps in managing infections and understanding the spread of diseases. == Summary: Cellular Biology and Viruses Eukaryotic Cells Nucleus: Membrane-bound organelle containing DNA. Compartments and Membranes: ○ Lipid Bilayer: Forms the basic structure of cellular membranes. Cellular Organelles and Their Functions Nucleus: Stores genetic information and controls cellular activities. Ribosomes: Produce proteins by translating mRNA. Endoplasmic Reticulum (ER): ○ Smooth ER: Synthesizes lipids and detoxifies chemicals. ○ Rough ER: Studded with ribosomes; involved in protein synthesis. Golgi Apparatus: Modifies, sorts, and packages proteins and lipids; involved in carbohydrate and polysaccharide synthesis. Lysosomes: Contain hydrolytic enzymes for breaking down waste materials and cellular debris. Peroxisomes: Perform oxidation reactions; involved in detoxifying harmful substances. Mitochondria: Produce ATP through oxidative phosphorylation; involved in β-oxidation and the TCA cycle. Prokaryotic Cells Bacterial Cells: ○ No Nucleus: DNA is circular and located in the cytoplasm. ○ Lack Membrane-Bound Organelles: Ribosomes are smaller (70S). ○ Cell Wall: Contains peptidoglycan (Gram-positive) or an outer membrane (Gram-negative). ○ Other Features: Plasmid DNA, capsule, flagella, surface-layer. Archaeal Cells: ○ No Nucleus: DNA is circular and located in the cytoplasm. ○ Lack Membrane-Bound Organelles: Ribosomes are smaller (70S). ○ Unique Cell Membrane: Contains phospholipids with ether linkages and branched fatty acid chains. ○ Cell Wall: Contains pseudopeptidoglycan, not peptidoglycan. ○ Extremophiles: Often found in extreme environments. Viruses Non-living Particles: Require a host cell to replicate. Structure: ○ Genetic Material: DNA or RNA. ○ Capsid: Protein or lipid-protein coat surrounding the genetic material. Replication: Inside a host cell using the host's machinery to produce new viral particles, which can lead to cell lysis and spread of the virus. == Part 1: Eukaryotic and Prokaryotic Cells Eukaryotic Cells: ○ Contain a nucleus. ○ Compartments and membranes: Involved in transport (covered in Lecture 2). ○ Organelles and Functions: Nucleus: Contains genetic material. Ribosomes: Produce proteins. ER (Smooth and Rough): Synthesis and transport. Golgi Apparatus: Carbohydrate and polysaccharide synthesis, secretory pathway. Lysosomes: Hydrolytic enzymes for digestion. Peroxisomes: Oxidation reactions. Mitochondria: ATP production, β-oxidation, TCA cycle. Prokaryotic Cells: ○ Bacterial Cells: No nucleus, single circular DNA. Cytoplasm lacks membrane-bound organelles. Smaller ribosomes (70S). Features like plasmid DNA, capsule, flagella, and surface-layer. ○ Archaeal Cells: Similar to bacteria but with unique cell membrane and wall characteristics. Often found in extreme environments. Cell walls contain pseudopeptidoglycan. Part 2: The Cell Cycle, Meiosis, and Differentiation Cell Division: ○ Mitosis: Produces two identical daughter cells with the same number of chromosomes. ○ Meiosis: Produces four non-identical daughter cells with half the chromosome number, crucial for sexual reproduction. Cell Differentiation: Process by which cells become specialized in structure and function. Part 3: The Cell Cycle, Differentiation, and Microscopy Understanding Cell Division: ○ Detailed stages in mitosis and meiosis. Cell Differentiation: ○ Importance in multicellular organisms. Microscopy: Techniques and terminology used to observe cells and their stages. == The Cell Cycle and Mitosis Mitosis Overview: Purpose: Accurate segregation of chromosomal DNA to produce two genetically identical daughter cells. Regulation: Controlled by the cell-cycle control system, which ensures that the cell cycle progresses properly. Phases of the Cell Cycle: 1. G1 Phase (First Gap Phase): ○ Function: Cell grows physically larger, duplicates organelles, and synthesizes molecular building blocks needed for DNA synthesis. ○ Key Events: Increase in cell size, production of proteins and organelles. 2. S Phase (Synthesis Phase): ○ Function: DNA replication occurs, producing two identical copies of each chromosome. ○ Key Events: Centrosome duplication to aid in DNA segregation. 3. G2 Phase (Second Gap Phase): ○ Function: Cell continues to grow and produce proteins, preparing for mitosis. ○ Key Events: Final preparations for mitosis, including additional protein synthesis and organelle replication. 4. M Phase (Mitosis): ○ Function: Division of the cell nucleus and cytoplasm into two daughter cells. ○ Phases within M Phase: Prophase: Chromosomes condense, the nuclear envelope breaks down, and the mitotic spindle begins to form. Prometaphase: The nuclear envelope is fully dissolved, and spindle fibers attach to the centromeres of chromosomes. Metaphase: Chromosomes align at the cell's equatorial plane. Anaphase: Sister chromatids are pulled apart to opposite poles of the cell. Telophase: Nuclear envelopes re-form around each set of chromosomes, and chromosomes de-condense. Cytokinesis: Division of the cytoplasm, resulting in two separate daughter cells. Summary of Mitosis: Mitosis: Refers to the division of the nucleus and its contents, including the chromosomes. It is a series of phases (prophase, prometaphase, metaphase, anaphase, telophase) that ensure proper chromosome separation. Cytokinesis: Completes cell division by dividing the cytoplasm into two daughter cells. Important Points: The cell cycle consists of distinct phases that prepare the cell for division and ensure accurate DNA replication and distribution. Mitosis involves both nuclear division and cytokinesis to produce two separate daughter cells, each with a complete set of chromosomes. == M Phase - Prophase Prophase Overview: Purpose: Initiates the process of chromosome segregation by preparing chromosomes for separation. Key Events in Prophase: 1. Chromosome Condensation: ○ Action: Sister chromatids condense into visible chromosomes. ○ Mechanism: Condensin proteins help in the condensation process, making the chromosomes more compact and manageable for segregation. 2. Mitotic Spindle Formation: ○ Action: The mitotic spindle begins to assemble. ○ Components: Centrioles: Move to opposite poles of the cell. Microtubules: Polymerize from the centrosomes, forming the spindle apparatus. ○ Function: The spindle apparatus is crucial for separating sister chromatids and ensuring they are evenly distributed to the daughter cells. 3. Nuclear Envelope Breakdown (usually overlaps with prophase): ○ Action: The nuclear envelope begins to disintegrate, allowing spindle fibers to access the chromosomes. Visual Representation: Chromosome Appearance: Chromosomes are visible as distinct, condensed structures. Centrosomes: Positioned at opposite poles, with microtubules extending towards the center of the cell. Mitotic Spindle: Appears as a network of microtubules spanning between the centrosomes. Summary of Prophase: Prophase is the first step in mitosis where chromosomes condense, and the mitotic spindle begins to form. This phase is critical for preparing the chromosomes for accurate separation during the subsequent stages of mitosis. == M Phase - Prometaphase Prometaphase Overview: Purpose: Facilitates the attachment of chromosomes to the mitotic spindle and ensures their proper alignment for separation. Key Events in Prometaphase: 1. Breakdown of the Nuclear Envelope: ○ Action: The nuclear envelope disintegrates, allowing the spindle microtubules to access and interact with the chromosomes. ○ Importance: Essential for spindle assembly and chromosome segregation. 2. Chromosome Attachment to Spindle Microtubules: ○ Action: Chromosomes attach to the spindle microtubules via kinetochores, which are protein complexes located at the centromeres of the chromosomes. ○ Function: This attachment ensures that chromosomes are properly aligned and attached to the spindle apparatus for accurate separation. Visual Representation: Chromosomes: Fully condensed and equipped with kinetochores. Spindle Microtubules: Extend from the centrosomes and attach to the kinetochores of the chromosomes. Nuclear Envelope: Fully disintegrated, allowing spindle fibers to reach the chromosomes. Metaphase (Following Prometaphase): Metaphase Overview: Purpose: Ensures that chromosomes are properly aligned at the cell's equatorial plane (metaphase plate) for accurate segregation. Key Events in Metaphase: 1. Chromosome Alignment: ○ Action: Chromosomes align at the equatorial plane of the cell. ○ Importance: This alignment ensures that each daughter cell will receive one copy of each chromosome. 2. Chromosome Visualization: ○ Action: Chromosomes are most clearly visible during metaphase because they are fully condensed and aligned. ○ Importance: Metaphase is often used in experiments to visualize and analyze chromosomes, as they can be easily observed and counted. Summary of Prometaphase and Metaphase: Prometaphase: Involves the breakdown of the nuclear envelope and the attachment of chromosomes to the spindle microtubules via kinetochores. Metaphase: Chromosomes align at the metaphase plate, ensuring proper distribution to the daughter cells. This stage is critical for accurate chromosome segregation and is often used for chromosomal analysis. == M Phase - Metaphase Metaphase Overview: Purpose: Ensures that all chromosomes are correctly aligned and attached to the spindle apparatus for accurate separation. Key Events in Metaphase: 1. Chromosome Alignment: ○ Action: Chromosomes are aligned at the equatorial plane of the cell, known as the metaphase plate. ○ Importance: This alignment ensures that each chromosome is properly positioned to be evenly distributed between the two daughter cells. 2. Kinetochore Microtubules: ○ Action: Kinetochore microtubules, which are part of the mitotic spindle, attach to the kinetochores located at the centromeres of the sister chromatids. These microtubules connect each chromatid to opposite spindle poles. ○ Function: This attachment is crucial for pulling the chromatids apart during anaphase. Metaphase Checkpoint: Purpose: Acts as a crucial checkpoint to ensure that the cell is ready to proceed with mitosis. Function: Verifies that: ○ Chromosomes are Properly Aligned: Ensures all chromosomes are aligned at the metaphase plate. ○ Proper Attachment: Ensures that each kinetochore is correctly attached to spindle microtubules from opposite poles. ○ No Errors in Chromosome Number: Checks for any chromosomal abnormalities or errors in attachment. Decision Point: If everything is correct, the cell proceeds to anaphase. If not, the cell cycle is halted to correct any issues. Importance of the Checkpoint: Prevents Errors: Ensures that chromosome segregation occurs accurately, preventing conditions such as aneuploidy, where cells have an abnormal number of chromosomes. Maintains Cell Integrity: Guarantees that only healthy cells complete mitosis and divide, maintaining overall cell and organismal health. == M Phase - Anaphase Anaphase Overview: Purpose: To ensure that sister chromatids are separated and moved to opposite poles of the cell, resulting in two sets of chromosomes. Key Events in Anaphase: 1. Separation of Sister Chromatids: ○ Action: Sister chromatids are pulled apart to form individual daughter chromosomes. ○ Mechanism: The protein separase degrades the cohesion proteins that hold the sister chromatids together, allowing them to separate. 2. Movement Toward Spindle Poles: ○ Action: The separated chromatids are pulled towards opposite spindle poles. ○ Mechanism: Kinetochore microtubules shorten, pulling the chromosomes toward the poles of the cell. 3. Spindle Pole Separation: ○ Action: The spindle poles move further apart. ○ Mechanism: Non-kinetochore microtubules (those not attached to kinetochores) slide past each other, pushing the spindle poles further apart, aiding in chromosome separation. Key Steps in Anaphase: Anaphase A: Chromosomes are pulled toward the spindle poles as the kinetochore microtubules shorten. Anaphase B: The spindle poles themselves move apart due to the sliding of non-kinetochore microtubules. Importance of Anaphase: Ensures Equal Chromosome Distribution: Guarantees that each daughter cell will receive an identical set of chromosomes. Prevents Chromosomal Abnormalities: Proper separation is crucial to avoid errors like aneuploidy, which can lead to various diseases and developmental issues. == M Phase - Telophase Telophase Overview: Purpose: To finalize the division of the cell, reform nuclear structures, and prepare the cell for the final step of cytokinesis. Key Events in Telophase: 1. Arrival and Decondensation of Chromosomes: ○ Action: Daughter chromosomes reach the poles of the cell and begin to decondense. ○ Mechanism: Chromosomes return to their less condensed, chromatin form, making them less visible under a microscope and preparing for transcription and further cell processes. 2. Reassembly of the Nuclear Envelope: ○ Action: The nuclear envelope reforms around each set of chromosomes at the poles. ○ Mechanism: Membrane vesicles from the endoplasmic reticulum fuse around the chromatin, creating two new nuclei within the cell. 3. Completion of Mitosis: ○ Action: Telophase marks the end of mitosis, completing the process of chromosome segregation. ○ Mechanism: All mitotic processes and checkpoints are concluded, ensuring that chromosomes are correctly distributed. 4. Contractile Ring Formation and Contraction: ○ Action: The contractile ring starts to contract, leading to cytokinesis. ○ Mechanism: The contractile ring, composed of actin and myosin filaments, pinches the cell membrane in the middle, facilitating the division of the cytoplasm and resulting in two separate daughter cells. Visual Summary: Chromosomes at the Poles: Chromosomes have reached the poles and are starting to decondense. Nuclear Envelope Formation: New nuclear envelopes are forming around the chromosomes at each pole. Contractile Ring: The ring around the middle of the cell is visible and beginning to contract. Importance of Telophase: Nuclear Reformation: Ensures that each daughter cell has a complete and functional nucleus. Preparation for Cytokinesis: Sets the stage for the final separation of the cell into two daughter cells. == Cytokinesis - The Final Step of the M Phase Cytokinesis Overview: Purpose: To divide the cytoplasm of the parent cell, resulting in two separate daughter cells, each with a complete set of organelles and chromosomes. Key Events in Cytokinesis: 1. Formation of the Contractile Ring: ○ Action: A contractile ring composed of actin and myosin filaments forms around the middle of the cell. ○ Mechanism: The ring contracts, pulling the plasma membrane inward and pinching the cell into two separate daughter cells. 2. Division of the Cytoplasm: ○ Action: The cytoplasm and organelles are distributed between the two daughter cells. ○ Mechanism: As the contractile ring continues to contract, it creates a cleavage furrow that deepens until the cell is pinched into two distinct cells. 3. Creation of Two Daughter Cells: ○ Action: The final product is two daughter cells, each with its own nucleus and a complete set of organelles and chromosomes. ○ Mechanism: The daughter cells are genetically identical to each other and to the parent cell. 4. Reformation of Interphase Structures: ○ Action: After cytokinesis, the cells enter interphase, during which the cell cycle resumes with normal functions and growth. ○ Mechanism: Microtubules and other cytoskeletal elements reorganize to support the new cell's activities and prepare for the next cell cycle. Visual Summary: Contractile Ring Formation: Actin and myosin filaments form a ring around the cell’s equator. Cleavage Furrow: The ring contracts, creating a furrow that deepens to separate the cell. Two Daughter Cells: The result is two distinct daughter cells, each with a complete set of chromosomes and organelles. Importance of Cytokinesis: Final Separation: Ensures that each daughter cell has a complete set of cellular components and a full complement of chromosomes. Preparation for New Cell Cycle: Each daughter cell enters interphase, ready to start the next round of the cell cycle. == The Cell Cycle - Mitosis and Meiosis Mitosis Overview: Definition: Mitosis is the process of cell division that results in two daughter cells, each with the same number of chromosomes as the parent cell. Purpose: To enable growth, repair, and maintenance of tissues by creating new cells that are genetically identical to the parent cell. Occurrence: Mitosis occurs in all somatic (body) cells, excluding gametes. Key Points in Mitosis: 1. Chromosome Duplication: Before mitosis begins, the cell’s chromosomes are duplicated during the S phase of interphase. 2. Phases of Mitosis: ○ Prophase: Chromosomes condense, spindle fibers form, and the nuclear envelope breaks down. ○ Prometaphase: Chromosomes attach to spindle fibers via kinetochores. ○ Metaphase: Chromosomes align at the cell’s equator. ○ Anaphase: Sister chromatids separate and move toward opposite poles. ○ Telophase: Chromosomes de-condense, and the nuclear envelope re-forms around each set of chromosomes. ○ Cytokinesis: The cytoplasm divides, forming two daughter cells. Meiosis Overview: Definition: Meiosis is the process of cell division that results in four genetically diverse daughter cells, each with half the number of chromosomes as the parent cell. Purpose: To produce gametes (sperm and eggs) for sexual reproduction, ensuring genetic diversity and the maintenance of chromosome number across generations. Occurrence: Meiosis occurs in germ cells (cells that produce gametes). Key Points in Meiosis: 1. Chromosome Duplication: Similar to mitosis, chromosomes are duplicated before meiosis begins. 2. Phases of Meiosis: ○ Meiosis I: Prophase I: Homologous chromosomes pair up and exchange genetic material (crossing over). Metaphase I: Homologous chromosomes align at the equator. Anaphase I: Homologous chromosomes separate and move to opposite poles. Telophase I and Cytokinesis: Two haploid cells are formed, each with half the number of chromosomes. ○ Meiosis II: Prophase II: Chromosomes condense again. Metaphase II: Chromosomes align at the equator. Anaphase II: Sister chromatids separate. Telophase II and Cytokinesis: Four haploid cells are formed, each with a unique combination of genetic material. Understanding Mitosis and Meiosis: Mitosis: Produces two identical cells with the same chromosome number as the parent cell. Essential for growth and repair. Meiosis: Produces four genetically unique cells with half the chromosome number of the parent cell. Essential for reproduction and genetic diversity. Resources for Further Study: Educational Videos: Many resources, such as YouTube videos, offer visual explanations of both mitosis and meiosis. These can provide additional clarity and help reinforce understanding. == Meiosis Overview Meiosis Definition: Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in four haploid cells, each with a single set of chromosomes. This process is crucial for sexual reproduction and the formation of gametes (sperm and egg cells). Process of Meiosis: 1. Meiotic S Phase: ○ Before meiosis begins, the cell undergoes DNA replication, resulting in chromosomes that each consist of two sister chromatids. 2. Meiosis I (First Meiotic Division): ○ Prophase I: Homologous chromosomes pair up and exchange genetic material through crossing over, leading to genetic diversity. ○ Metaphase I: Homologous chromosomes align at the cell's equator. ○ Anaphase I: Homologous chromosomes are pulled to opposite poles, reducing the chromosome number by half. ○ Telophase I and Cytokinesis: The cell divides into two haploid cells, each with half the original number of chromosomes. 3. Meiosis II (Second Meiotic Division): ○ Prophase II: Chromosomes condense again, and new spindle fibers form in each haploid cell. ○ Metaphase II: Chromosomes align at the equator of each cell. ○ Anaphase II: Sister chromatids are pulled apart to opposite poles of each cell. ○ Telophase II and Cytokinesis: The two haploid cells from Meiosis I divide again, resulting in four haploid gametes, each with a unique combination of chromosomes. Importance of Meiosis: Chromosome Number Reduction: Meiosis ensures that gametes (sperm and egg cells) have half the number of chromosomes (haploid), so when fertilization occurs, the resulting zygote has the correct diploid number of chromosomes (46 in humans). Genetic Diversity: The process of crossing over and the random assortment of chromosomes contribute to genetic variation in offspring. Somatic vs. Germ Cells: Somatic Cells: These are all body cells except for sperm and egg cells. They are diploid (2n), meaning they have two sets of chromosomes (46 in humans). Germ Cells: These are the reproductive cells (sperm and eggs) that are haploid (n), meaning they have one set of chromosomes (23 in humans). Key Concepts: Diploid (2n): Cells with two sets of chromosomes (e.g., somatic cells). Haploid (n): Cells with one set of chromosomes (e.g., gametes). Visual Aids and Further Study: Educational videos and diagrams are helpful for visualizing the stages of meiosis and understanding the chromosome segregation process. Summary: Mitosis produces two identical diploid cells, maintaining chromosome number. Meiosis produces four genetically diverse haploid cells, reducing chromosome number by half and ensuring proper chromosome number in sexually reproducing organisms. == Summary of Meiosis in Eukaryotes Diploid Cells: Definition: Have chromosomal pairs. Types: ○ Somatic Cells: These are body cells that do not pass genetic information to offspring. ○ Germ-line Cells: These are reproductive cells (sperm and eggs) that pass genetic information to offspring. Haploid Cells: Definition: Have one set of chromosomes. Function: Created through meiosis and combine during fertilization to restore the diploid number of chromosomes (e.g., 46 in humans). Process of Meiosis: 1. Meiotic S Phase: DNA replication occurs. 2. Meiosis I: Homologous chromosomes are separated, reducing the chromosome number by half. 3. Meiosis II: Sister chromatids are separated, resulting in four haploid cells. Importance: Genetic Variation: Meiosis introduces genetic diversity through processes such as crossing over and independent assortment. Chromosomal Abnormalities: Variations in chromosome number (e.g., trisomy or monosomy) can lead to genetic disorders due to improper protein production. == Meiosis - Homologous Recombination in Metaphase of Meiosis I Homologous Recombination (Crossing Over): Definition: A process where homologous chromosomes exchange genetic material during meiosis. Occurrence: Takes place during Metaphase I of meiosis, where homologous chromosomes align and physically exchange segments. Steps and Effects: 1. Chromosome Pairing: ○ Homologous chromosomes come together and pair up, forming a tetrad. 2. Exchange of Genetic Material: ○ Sections of chromatids from one homologous chromosome are swapped with corresponding sections from the other homologous chromosome. ○ This results in chromosomes with a mixture of maternal and paternal genes. 3. Genetic Variation: ○ Crossing over creates new combinations of alleles, leading to genetic diversity in the resulting gametes. ○ This increases the variability of offspring, as each gamete contains a unique combination of genetic information. Benefits of Crossing Over: Increased Genetic Diversity: ○ By producing gametes with different combinations of genes, crossing over enhances genetic variation within a population. ○ This variation is crucial for evolution and adaptation to changing environments. Enhanced Survival: ○ Populations with higher genetic diversity have a better chance of survival in varying conditions because different individuals may possess traits that allow them to thrive in different environments. ○ For example, in a changing climate, genetic diversity increases the likelihood that some individuals will have traits suited to new conditions. Implications: Individual Variation: ○ The genetic recombination process contributes to the uniqueness of each individual, even within a family, as each offspring inherits a different combination of genes from their parents. Survival and Evolution: ○ The increased genetic variation due to crossing over can lead to better adaptability and survival of species over time. == Cell Differentiation Definition: Cell differentiation is the process by which unspecialized cells become specialized into distinct types with specific functions. This is crucial for the formation of complex multicellular organisms where different cells perform unique roles. Levels of Differentiation: 1. Totipotent: ○ Definition: Cells that have the potential to develop into any cell type in the organism, including extra-embryonic tissues like the placenta. ○ Example: The zygote and the first few cell divisions after fertilization. 2. Pluripotent: ○ Definition: Cells that can give rise to any cell type in the body, but not extra-embryonic tissues. ○ Example: Embryonic stem cells. They can differentiate into all three primary germ layers: endoderm, mesoderm, and ectoderm. ○ Germ Layers: Endoderm: Forms internal structures like the digestive and respiratory systems. Mesoderm: Forms structures like muscles, bones, and blood. Ectoderm: Forms external structures like skin and nervous system. 3. Multipotent: ○ Definition: Cells that can differentiate into a limited range of cell types, usually within a specific tissue or organ. ○ Example: Hematopoietic stem cells in the bone marrow that can become various types of blood cells (e.g., red blood cells, white blood cells). 4. Oligopotent: ○ Definition: Cells that can differentiate into a few closely related cell types. ○ Example: Lymphoid stem cells that can develop into various types of blood cells such as B cells and T cells. 5. Unipotent: ○ Definition: Cells that can only differentiate into one specific type of cell. ○ Example: Skin stem cells that can only produce skin cells. Summary of Differentiation: Embryonic Stem Cells: Totipotent or pluripotent, capable of differentiating into any cell type. Adult Stem Cells: Generally multipotent or oligopotent, specialized for maintaining and repairing tissues. Somatic Cells: Fully differentiated cells that perform specific functions and do not have the potential to transform into other cell types. == Cell Differentiation and Stem Cells Cell Differentiation: Definition: The process by which cells become specialized to perform specific functions in a multicellular organism. Organization: Specialized cells form tissues, tissues form organs, and organs form systems within the body. Types of Stem Cells: 1. Totipotent Stem Cells: ○ Definition: Can differentiate into any cell type, including extra-embryonic tissues. ○ Example: Zygote and the first few cell divisions (up to the blastocyst stage). 2. Pluripotent Stem Cells: ○ Definition: Can become any cell type within the three primary germ layers (endoderm, mesoderm, ectoderm) but not extra-embryonic tissues. ○ Example: Embryonic stem cells (ESCs) derived from the blastocyst stage (3-5 days old). 3. Multipotent Stem Cells: ○ Definition: Can differentiate into a limited range of cell types within a specific tissue or organ. ○ Example: Hematopoietic stem cells in the bone marrow. 4. Oligopotent Stem Cells: ○ Definition: Can differentiate into a few closely related cell types. ○ Example: Lymphoid stem cells that can become various types of blood cells like B cells and T cells. 5. Unipotent Stem Cells: ○ Definition: Can differentiate into only one specific type of cell. ○ Example: Skin stem cells that produce only skin cells. Embryonic Stem Cells (ES Cells): Stage of Origin: Derived from early-stage embryos (blastocyst stage, 3-5 days old). Characteristics: Highly versatile, capable of differentiating into nearly any cell type in the body. Cultivation: Can be grown in the lab and used for various research and therapeutic applications. Controversies and Ethical Considerations: Embryonic Stem Cell Research: ○ Controversy: Ethical concerns arise from the use of human embryos for stem cell research, as extracting stem cells typically involves destroying the embryo. ○ Benefits: Potential to treat a range of diseases and conditions by regenerating damaged tissues and organs. ○ Ethical Debates: Issues surrounding the moral status of embryos and the implications of their use in research and therapy. Adult Stem Cells: Definition: Found in small numbers in various adult tissues; less versatile compared to embryonic stem cells. Examples: Bone marrow stem cells used in treatments for blood disorders. Applications: Used in therapies such as bone marrow transplants to treat conditions like leukemia. Future of Stem Cell Research: Advancements: Continued research may lead to new therapies and techniques for disease treatment and tissue regeneration. Ethical and Political Developments: Future policies and ethical considerations will likely evolve, potentially leading to broader acceptance and application of stem cell technologies. == Mitosis: Purpose: Produces two genetically identical daughter cells. Phases: ○ G1 (Growth Phase): Cell growth and preparation for DNA replication. ○ S-Phase (Synthesis Phase): DNA is replicated. ○ G2 (Growth Phase): Final preparation for mitosis. ○ M-Phase (Mitosis and Cytokinesis): Cell division occurs. Mitosis Stages: Prophase: Chromosomes condense, spindle apparatus forms. Prometaphase: Spindle fibers attach to chromosomes. Metaphase: Chromosomes align at the cell’s equator. Anaphase: Sister chromatids separate and move to opposite poles. Telophase: Chromosomes de-condense, nuclear envelopes reform. Cytokinesis: Cytoplasmic division resulting in two daughter cells. Meiosis: Purpose: Produces haploid cells with one set of chromosomes. Meiosis I: ○ Homologous Recombination: Exchange of genetic material between homologous chromosomes. Meiosis II: ○ Similar to Mitosis: Separation of sister chromatids. Cell Differentiation: Definition: Process by which cells become specialized for specific functions. Types of Stem Cells: ○ Totipotent: Can differentiate into any cell type, including extra-embryonic tissues. ○ Pluripotent: Can differentiate into any cell type within the three germ layers (endoderm, mesoderm, ectoderm). ○ Multipotent: Can differentiate into a limited range of cell types within a specific tissue or organ. ○ Oligopotent: Can differentiate into a few closely related cell types. ○ Unipotent: Can differentiate into only one specific type of cell. ==

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