Cell Biology Concepts

• Prokaryotic cells are defined as "before kernel" (no nucleus), while eukaryotic cells are "true kernel" (with nucleus).
• Eukaryotic cells possess a defined nucleus enclosed by a nuclear envelope, whereas prokaryotic cells have DNA in a nucleoid region.
• Eukaryotic cells contain membrane-bound organelles, while prokaryotic cells have only ribosomes.
• Prokaryotic cells are generally smaller (0.1-5.0 µm) compared to eukaryotic cells (10-100 µm).
• Eukaryotic cells are more complex, with specialized structures, while prokaryotic cells are considered primitive.
• Bacteria and archaea are examples of prokaryotic cells; plant and animal cells are examples of eukaryotic cells.
• All cells contain a genome (DNA), cytoplasm, and ribosomes, indicating a common ancestry.
• Ribosomes are crucial for protein synthesis, translating mRNA into proteins.
• Cytoplasm is the gel-like substance within the cell membrane, suspending organelles.
• The cell membrane regulates substance movement in and out of the cell, maintaining homeostasis.
• Plant cells have a cell wall for structural support, absent in animal cells.
• DNA is organized into chromatin in the nucleus, condensing to form chromosomes during cell division.

Endoplasmic Reticulum (ER)

• ER is a network of membrane tubes adjacent to the nucleus
• Rough ER is studded with ribosomes, involved in protein synthesis and packaging
• Smooth ER lacks ribosomes, functions in lipid synthesis and detoxification
• Ribosomes on Rough ER allow direct protein synthesis, while Smooth ER is involved in metabolic processes.
• Proteins synthesized in the Rough ER are transported to the Golgi apparatus for further processing.
• Dysfunction in ER can lead to diseases such as cystic fibrosis due to improper protein folding.

Golgi Apparatus

• The Golgi apparatus is composed of flattened membrane-bound sacs.
• It modifies, sorts, and packages proteins for secretion or delivery to other organelles.
• The Golgi apparatus involves glycosylation and phosphorylation of proteins during chemical modifications.
• Vesicles are utilized to transport proteins to their destinations
• It is essential for the secretion of hormones and enzymes.
• Antibody production in plasma cells involves the Golgi apparatus for processing before secretion.

Mitochondria

• Mitochondria features a double membrane, with a smooth outer membrane and an inner membrane folded into cristae.
• It is the site of ATP production through cellular respiration.
• The Krebs cycle occurs in the mitochondrial matrix; the electron transport chain occurs in the inner membrane.
• It converts energy from macromolecules into usable ATP.
• Inner membrane folding increases surface area, enhancing ATP production efficiency.
• Mitochondrial dysfunction can lead to metabolic disorders and diseases.

Lysosomes and Vacuoles

• Lysosomes are membrane-enclosed sacs with hydrolytic enzymes for digesting macromolecules and damaged cell parts.
• They're involved in programmed cell death (apoptosis) and recycling cellular components.
• Vacuoles are membrane-bound sacs that store water, nutrients, and waste products.
• Large central vacuoles maintain turgor pressure, essential for plant structure.
• Both organelles play critical roles in maintaining cellular homeostasis and waste management.
• Lysosomal storage diseases result from enzyme deficiencies, leading to waste accumulation.

Chloroplasts

• Chloroplasts are double-membrane organelles found in plant cells and some algae.
• It is the site of photosynthesis, converting sunlight into chemical energy (sugar).
• Thylakoids offer membrane compartments organized in stacks (grana) containing chlorophyll for light absorption.
• Stroma refers to the fluid surrounding thylakoids where the Calvin cycle occurs for carbon fixation.
• Folding of thylakoid membranes increases surface area for light absorption.
• Understanding chloroplast function is crucial for agricultural biotechnology and improving crop yields.

Importance of Cell Size

• Smaller cells are more efficient in nutrient uptake and waste elimination.
• A higher surface area to volume ratio allows for better exchange of materials with the environment.
• As cells grow larger, their volume increases faster than surface area, hindering resource exchange.
• Cells adapt with microvilli in intestines to increase surface area.
• Villi and microvilli in the digestive system enhance nutrient absorption.
• Root hairs increase surface area for water and mineral absorption.

Structure Dictates Function

• Different cell types have unique structures related to their specific functions.
• Neurons have long axons for signal transmission, while red blood cells are biconcave for efficient gas exchange.
• Plant cells have rigid cell walls and chloroplasts, while animal cells have lysosomes and centrioles.
• Cell structure directly influences its role in the organism's physiology.
• Understanding cell structure-function relationships is essential in fields like medicine and biotechnology.
• Studies on cell differentiation and specialization inform regenerative medicine and stem cell research.

Antibody Production

• Antibodies are proteins made by plasma cells, a type of white blood cell.
• They're crucial for immune response, identifying and neutralizing pathogens.
• Antibody production starts with B cell activation, differentiating into plasma cells.
• Plasma cells synthesize antibodies in response to specific antigens.
• Antibodies are secreted into the bloodstream to target and eliminate pathogens.

Antibody Pathway

• The endomembrane system includes the endoplasmic reticulum (ER), Golgi apparatus, and vesicles.
• Step 1: Antibody synthesis occurs in the rough ER, where ribosomes translate mRNA into polypeptide chains.
• Step 2: The newly formed antibodies are folded and modified in the ER lumen.
• Step 3: Transport vesicles bud off from the ER and carry the antibodies to the Golgi apparatus.
• Step 4: In the Golgi apparatus, the antibodies undergo further modifications, such as glycosylation.
• Step 5: Secretory vesicles containing the antibodies fuse with the plasma membrane, releasing them outside the cell.

Plasma Membrane Characteristics

• The plasma membrane is selectively permeable.
• It serves as a boundary, maintaining the cell's internal environment while regulating material transport.
• The fluid mosaic model describes the plasma membrane as a dynamic structure
• Hydrophobic interactions primarily hold the membrane together, allowing for fluidity and flexibility.

Fluid Mosaic Model Components

• Cholesterol stabilizes membrane fluidity under varying temperatures.
• Carbohydrates, attached to proteins (glycoproteins) or lipids (glycolipids), serve as recognition sites for cell signaling.
• Phospholipids form a bilayer with hydrophilic heads outward and hydrophobic tails inward.

Membrane Proteins

• Membrane proteins are classified as peripheral (loosely attached) or integral (spanning the membrane).
• Integral proteins often function as transport channels/receptors; peripheral proteins are involved in signaling and maintaining shape.
• Functions of membrane proteins include transport, cell recognition, enzymatic activity, signal transduction, intercellular joining, and attachment to the cytoskeleton.

Passive Transport

• Passive transport doesn't use energy (ATP) and moves substances down their concentration gradient.
• Types include diffusion, osmosis, and facilitated diffusion.
• Gases like O2 and CO2 are transported this way, along with glucose via transport proteins.

Active Transport

• Active transport requires energy to move substances against their concentration gradient.
• Examples include the Na+/K+ pump and proton pumps.
• Cotransport mechanisms utilize the energy from one gradient to transport another substance.

Bulk Transport

• Bulk transport involves the movement of large molecules or particles via vesicles and requires energy.
• Endocytosis involves engulfing macromolecules in vesicles.
• Phagocytosis, pinocytosis and receptor-mediated endocytosis are three types of endocytosis
• Exocytosis involves expelling materials from the cell by vesicles fusing with the plasma membrane.

Selective Permeability

• The plasma membrane's selective permeability allows small nonpolar molecules to pass freely while restricting larger polar molecules and ions.
• Small polar molecules like water can pass through in limited amounts, while large polar molecules require transport proteins.
• This is crucial for maintaining homeostasis within the cell.

Transport Proteins

• Channel proteins form hydrophilic tunnels for specific movement.
• Aquaporins are an example of channel protein (water).
• Carrier proteins change shape to transport molecules across the membrane.
• Glucose transporters are a type of carrier protein.
• Ion channels facilitate the movement of ions across the membrane.
• Na+/K+ pumps are an example of ion channels

Phagocytosis

• Phagocytosis or 'cellular eating', involves engulfing large particles or even other cells.
• Macrophages, immune cells, use phagocytosis to eliminate pathogens.
• Engulfed material is enclosed in a phagosome, fusing with lysosomes for digestion.
• White blood cells engulfing bacteria protect the body from infection.
• Phagocytosis plays a significant role in tissue remodeling and homeostasis.

Pinocytosis

• Pinocytosis, or 'cellular drinking', involves uptake of extracellular fluid and dissolved substances.
• Cells sample their environment and absorb nutrients via this process.
• Intestinal epithelial cells utilize pinocytosis to absorb nutrients from the gut.
• Vesicles formed during pinocytosis are smaller than those formed during phagocytosis.
• It is essential for maintaining cellular homeostasis and nutrient acquisition.

Receptor-Mediated Endocytosis

• Receptor proteins on the cell membrane bind specific ligands.
• Allows for selective uptake of molecules such as hormones and nutrients.
• LDL receptors allow for the uptake of cholesterol.
• Begins with ligand binding, leading to the invagination of the membrane and vesicle formation.
• It is crucial for regulating cellular responses to external signals.

Passive Transport

• Does not require energy (ATP) and occurs along the concentration gradient.
• Types include diffusion, osmosis, and facilitated diffusion through transport proteins.
• Oxygen and carbon dioxide diffuse across cell membranes due to concentration differences.
• Osmosis specifically refers to the movement of water across a semipermeable membrane.
• It is vital for maintaining homeostasis within cells.

Active Transport

• Requires energy (ATP) to move substances against their concentration gradient.
• Essential for maintaining ion gradients, such as sodium and potassium across the membrane.
• The Na+/K+ pump actively transports 3 Na+ ions out and 2 K+ ions into the cell.
• Crucial for nutrient uptake and waste removal in cells.
• Allows cells to maintain internal concentrations that differ from their external environment.

Osmolarity and Tonicity

• Osmolarity is the total solute concentration in a solution, influencing water movement.
• Tonicity refers to the relative solute concentrations between two solutions, affecting cell shape.
• Hypertonic solutions cause animal cells to shrink, isotonic solutions maintain normal shape, and hypotonic solutions can lead to cell lysis.
• Hypertonic solutions cause plant cells to undergo plasmolysis, isotonic solutions result in flaccidity, and hypotonic solutions create turgidity.
• Water movement is driven by osmotic gradients, emphasizing the importance of solute concentration.

Water Potential

• Water potential (ψ) measures the tendency of water to move by osmosis (ψ = ψS + ψP).
• Solute potential (ψS) is influenced by solute concentration, while pressure potential (ψP) is affected by physical pressure.
• The more negative the water potential, the greater the tendency for water to move into that area.
• Example: In plant cells, turgor pressure is vital for maintaining structure and function.
• Increasing solute concentration decreases water potential, while increasing pressure potential raises it.
• Water moves from areas of high ψ to low ψ.

Advantages of Compartmentalization

• Cellular compartments allow for simultaneous metabolic processes, enhancing efficiency.
• Membranes minimize interference between different biochemical reactions occurring within the cell.
• Lysosomes maintain an acidic environment for hydrolytic enzymes, while the cytoplasm remains neutral.
• Mitochondria and chloroplasts have distinct compartments that optimize energy production and photosynthesis.
• Compartmentalization is a key feature of eukaryotic cells, allowing for specialization of functions.

Origins of Cell Compartmentalization

• Both prokaryotic and eukaryotic cells have a plasma membrane, but eukaryotes possess additional internal membranes.
• The nucleus and other organelles evolved from the infolding of the plasma membrane.
• Mitochondria and chloroplasts originated from free-living prokaryotes through endosymbiosis.
• The endosymbiotic theory posits that engulfed prokaryotes formed mutually beneficial relationships with host cells.
• Mitochondria and chloroplasts both have double membranes and circular DNA.

Explore fundamental cell biology concepts, including organelle function, cellular processes, and cell types. This quiz covers the Golgi apparatus, compartmentalization, prokaryotic vs. eukaryotic cells, and endosymbiotic theory.