Cells Chapter III PDF

 CHAPTER III. CELL AS THE UNIT OF LIFE ALVIN DOMINGO, MSc and ALTHEA JOMARI LAGAZO, MSc Faculty Department of Biological Sciences College of Arts and Sciences Learning Objectives 1. Identify and Describe the Key Components of an Animal C...

 CHAPTER III. CELL AS THE UNIT OF LIFE ALVIN DOMINGO, MSc and ALTHEA JOMARI LAGAZO, MSc Faculty Department of Biological Sciences College of Arts and Sciences Learning Objectives 1. Identify and Describe the Key Components of an Animal Cell 2. Explain the Functions of Animal Cell Organelles 3. Differentiate Animal Cell Types Animal Cell An animal cell: Is irregularly shaped. Is eukaryotic, containing a nucleus. Has a flexible membrane. Contains small molecular structures known as organelles, each with specific functions. Typically ranges in size from 10 to 30 micrometers, smaller than a human hair's diameter. Differs from other cells in that it lacks a cell wall, allowing it to adopt various shapes. This flexibility has facilitated the evolution and diversification of animal cells, contributing to the animal kingdom’s diversity. Animal Cell Size and Shape Animal cells vary widely in size, ranging from microscopic to millimeters. The largest known animal cell is the ostrich egg, over 5.1 inches across, while neurons are just 100 microns. Shapes include flat, oval, rod-shaped, curved, spherical, concave, and rectangular. Most are microscopic and require a microscope for observation. Animal cells are eukaryotic with a membrane-bound nucleus and DNA. They contain various organelles and structures with specific functions. The Discovery of cells The term "cells" originated in 1665, coined by British scientist Robert Hooke. Hooke conducted pioneering microscope studies, examining cork tissue and noting honeycomb-like structures, which he named "cells." Antonie Van Leuwenhoek's Contributions Antonie Van Leuwenhoek, a contemporary of Hooke, enhanced microscopy with more powerful lenses. He became the first person to observe human cells and bacteria through his improved microscope, expanding our understanding of the microscopic world. Animal Nucleu Cell Mitochondr s Nucleul us ion Rough endoplasmic Peroxiso Reticulum me Ribosom Lysosom es e Vacoul e Smooth endoplasmic Reticulum Centroso me Cytoskelet Golgi on apparatus Plasma membrane  What are Cell Organelles? Cellular components are known as cell organelles. Cell organelles can be membrane-bound or non-membrane-bound, each with distinct structures and functions. These organelles work together to ensure the cell functions properly. Some organelles provide shape and support, while others are involved in cell movement and reproduction. Organelles can be classified into three categories based on the presence or absence of a membrane. Organelles and their Primary Functions Genetic Control Cellular Protection Protein Synthesis and Processing Energy Production and Lipid Metabolism Storage and Structural Support Membrane-bo und Organelles  Nucleus Double-membraned organelle, central control, and DNA storage. Contains nucleoli and chromosomes with genes for trait inheritance. Exceptions: Some cells, like red blood cells (RBCs), lack a nucleus despite being eukaryotic.  Structure of Nucleus Typically, the most prominent organelle. Enclosed by the nuclear envelope, a double membrane. Separates cytoplasm from nuclear contents. Houses chromosomes containing DNA, critical for cell components and reproduction. Nucleus Function Contains hereditary information, controlling cell growth and reproduction. Membrane-bound structure housing genetic material. Facilitates DNA Replication, producing identical copies for cell division. Serves as the site of transcription, creating various RNA types from DNA. DNA-to-RNA-to-proteins: The central process in biology. Endoplasmic Reticulum “Endoplasmic Reticulum is a complex network of tubular membranes exclusively present in the cytoplasm of the eukaryotic cell.” Exists in two forms: rough ER (with ribosomes) and smooth ER (without ribosomes). Continuous membrane folds, extending to the nuclear membrane. Present in all eukaryotic cells except sperm and red blood cells.  ER Diagram Rough endoplasmic reticulum has ribosomes embedded within its structure, giving a “rough” appearance. The smooth endoplasmic reticulum does not have these ribosomes, hence appearing “smooth.” Rough Endoplasmic Reticulum (RER) Structure Named for its appearance: Flattened sacs with ribosomes on the surface. Responsible for synthesizing and secreting proteins (e.g., liver, glands). Prominent in cells with active protein synthesis, like hepatocytes. Smooth Endoplasmic Reticulum (SER) Structure Lacks ribosomes on its surface. Exhibits a tubular form. Involved in phospholipid production for cell membranes and metabolism. Functions in transporting products from rough ER to organelles, including the Golgi apparatus. Functions of Rough Endoplasmic Reticulum (RER) Primary role: Protein synthesis. Important for protein folding. Ensures quality control in protein folding. Key function: Protein sorting. Functions of Smooth Endoplasmic Reticulum (SER) Synthesizes critical lipids like phospholipids and cholesterol. Produces and secretes steroid hormones. Metabolizes carbohydrates. Stores and releases calcium ions, crucial for the nervous and muscular systems. Golgi Apparatus Also known as Golgi Incoming Transport complex or Golgi body, Lume Vesicle named after its discoverer n Camillo Golgi. Cisterna e Present in all eukaryotic cells, both in plants and animals. Outgoing A membrane-bound Trans TV organelle located in the Face cytosol of the cell. Golgi Apparatus Parts Cisternae: Flattened membrane sacs within the Golgi apparatus. Incoming Transport Lume Vesicle Lumen: The interior space or n cavity within Golgi cisternae. Incoming Transport Vesicle: Cisterna Vesicles bringing materials frome the endoplasmic reticulum to the Golgi. Outgoing Transport Vesicle: Transfac Vesicles carrying modified e molecules from the Golgi to Outgoing their destinations. TV Transface: The Golgi region where outgoing transport vesicles bud off for molecule delivery. Golgi Apparatus Structure Comprises 5 to 8 cup-shaped compartments called cisternae. Cisternae are flattened, stacked pouches within the Golgi apparatus. A typical Golgi stack contains 4 to 8 cisternae, but some protists may have around 60. Mammalian cells possess approximately 40 to 100 stacks of cisternae. Animal cells typically contain 10 to 20 Golgi stacks per cell, connected by tubular connections. The Golgi complex is commonly located near the nucleus. Golgi Apparatus Functions Main function: Packages and secretes proteins. Receives proteins from the Endoplasmic Reticulum. Packages proteins into membrane-bound vesicles for transport to various destinations (lysosomes, plasma membrane, or secretion). Participates in lipid transport and lysosome formation. Facilitates post-translational modification and enzymatic processing (e.g., phosphorylation, glycosylation). Site for the synthesis of glycolipids, sphingomyelin, and more. Mitochondria “Mitochondria are membrane-bound organelles present in the cytoplasm of all eukaryotic cells, that produce adenosine triphosphate (ATP), the main energy molecule used by the cell.” Structure of Mitochondria Double-membraned, rod-shaped organelle in plant and animal cells. Size: 0.5 to 1.0 micrometer in diameter. Comprises an outer membrane, inner membrane, and matrix (gel-like material). Outer and inner membranes consist of protein and phospholipid layers, separated by the intermembrane space. Outer membrane features numerous porins, specialized proteins. Structure of Mitochondria: Cristae and Matrix Cristae in Mitochondria The inner membrane of mitochondria forms folds known as cristae, increasing internal surface area. Cristae, along with inner membrane proteins, contribute to ATP production. Inner mitochondrial membrane is selectively permeable to oxygen and ATP molecules. Site for numerous crucial chemical reactions within mitochondria. Structure of Mitochondria: Cristae and Matrix Mitochondrial Matrix Viscous fluid with enzymes, proteins, ribosomes, ions, mitochondrial DNA, cofactors, and organic molecules. Enzymes in the matrix are vital for ATP synthesis.  Functions of Mitochondria Primary role: Energy production through oxidative phosphorylation. Regulates cell metabolism. Supports cell growth and multiplication. Detoxifies ammonia in liver cells. Involved in apoptosis (programmed cell death). Contributes to the production of blood components and hormones like testosterone and estrogen. Maintains cellular calcium ion concentration. Participates in cellular differentiation, signaling, senescence, cell cycle control, and growth. Peroxisome Peroxisomes Overview Small vesicles Single membrane-bound organelles Found in eukaryotic cells Functions of Peroxisomes Contain digestive enzymes Break down toxic materials in the cell House oxidative enzymes for metabolic activity Important for lipid production Convert reactive oxygen species (e.g., hydrogen peroxide) into safer molecules (water and oxygen) by catalase enzyme Peroxisome Heterogeneous Group Peroxisomes are a heterogeneous group of organelles. Marker enzymes distinguish them from other cell organelles. Variability in Peroxisome Structure Often exist as individual organelles, e.g., in fibroblasts. In liver cells, they can form interconnected tubules known as peroxisome reticulum. Peroxisome Structure Variability in Structure Shape, size, and number vary based on cell energy requirements. Membrane Composition Composed of a phospholipid bilayer. Contains numerous membrane-bound proteins. Enzymes and Protein Import Enzymes involved in lipid metabolism synthesized on free ribosomes. Enzymes selectively imported into peroxisomes. Peroxisome Target Sequence 1 (PTS1) is a common signaling sequence for import. Peroxisome Structure Phospholipid Synthesis Phospholipids in peroxisomes typically synthesized in the smooth endoplasmic reticulum. Growth and Division Peroxisomes grow in size due to the ingress of proteins and lipids. Eventually divide into two organelles. DNA Peroxisomes do not have their own DNA. Proteins are transported from the cytosol after translation. Peroxisome function The main function of peroxisome is in lipid metabolism and the processing of reactive oxygen species. Other peroxisome functions include: They take part in various oxidative processes. They take part in lipid metabolism and catabolism of D-amino acids, polyamines, and bile acids. The reactive oxygen species such as peroxides produced in the process is converted to water by various enzymes like peroxidase and catalase. In plants, peroxisomes facilitate photosynthesis and seed germination. They prevent loss of energy during photosynthesis carbon fixation. Lysosome Lysosomes: The "Suicide Bags" of the Cell Important organelles in eukaryotic animal cells. Notable for their peculiar function. Coined as the "suicide bags" of the cell. Discovery by Christian de Duve Term and concept introduced by Christian de Duve, a Belgian biologist. Awarded the Nobel Prize in Medicine or Physiology in 1974 for his work on lysosomes. Lysosome Definition “Lysosomes are sphere-shaped sacs filled with hydrolytic enzymes that have the capability to break down many types of biomolecules.” Lysosome Structure Lysosomal pH Level Lumen pH ranges between 4.5 and 5.0. Highly acidic environment, similar to stomach acids. Diverse Functions of Lysosomes Besides breaking down biological polymers, lysosomes play crucial roles in various cell processes: Counting and recycling discharged materials. Participating in energy metabolism. Contributing to cell signaling. Assisting in the restoration of the plasma membrane. Size Variability Lysosome sizes vary: Largest lysosomes can measure over 1.2 μm. Typically, lysosomes range from 0.1 μm to 0.6 μm. Why are Lysosomes known as Suicidal Bags? Lysosomes as Cellular Waste Disposers Lysosomes process and degrade undesirable materials. Responsible for breaking down waste from both outside and inside the cell. Autolysis: Self-Destruction of Lysosomes Occasionally, digestive enzymes within lysosomes can inadvertently damage the lysosomes themselves. This process is known as autolysis: "Auto" means "self." "Lysis" refers to "the disintegration of the cell by the destruction of its cell membrane." Vacuole “Vacuoles are membrane-bound cell organelles present in the cytoplasm and filled with a watery fluid containing various substances.” Vacuole Definition Vacuoles: "Empty Space" The term "vacuole" originates from "empty space." Essential organelles for storage and disposal of substances. Size Differences Plant cell vacuoles are significantly larger than those in animal cells. Plant vacuoles can occupy over 80% of the cell's volume. Number of Vacuoles Cells can have one or more vacuoles, depending on their needs. Vacuole Structure Vacuole Structure Vacuoles are membrane-bound structures within the cell's cytoplasmic matrix. The membrane surrounding the vacuole is called the tonoplast. Cell Sap The components inside the vacuole, known as cell sap, differ from those in the surrounding cytoplasm. Membrane Composition Vacuole membranes are composed of phospholipids. Vacuole Structure Proteins and Transport Membranes of vacuoles contain embedded proteins. These proteins play a crucial role in transporting molecules across the membrane. Versatile Function Different combinations of these membrane proteins enable vacuoles to store and hold various materials. Vacuole Function Storage Store salts, minerals, pigments, proteins, and lipids within the cell. Contains cell sap, maintaining an acidic environment within the cell. Turgor Pressure Filled with water, creating turgor pressure. Provides cell shape and resistance to extreme conditions. Endocytosis and Exocytosis Facilitate endocytosis, taking in substances. Assist in exocytosis, expelling substances. Isolate stored substances from the cytosol. Lysosomes and Digestion Lysosomes are vesicles that perform endocytosis to intake and digest food. Endocytosis varies among different cell types. Non-membran e-bound Organelles Ribosomes “Ribosomes are one of the most important cell organelles composed of RNA and protein that converts genetic code into chains of amino acids.” Ribosomes Ribosomes: Protein Synthesis Machinery Complex molecular machines found within living cells. Responsible for producing proteins from amino acids in a process known as protein synthesis or translation. Universal Function Protein synthesis is a primary function performed by all living cells. Ribosomes are essential for this process. Ribosomes Ubiquitous Presence Ribosomes are specialized cell organelles. Found in both prokaryotic and eukaryotic cells. Key Processes Ribosomes bind to messenger ribonucleic acid (mRNA). Decode information carried by mRNA's nucleotide sequence. Utilize transfer RNAs (tRNAs) containing amino acids. tRNAs enter the ribosome at the acceptor site. Ribosomes facilitate the addition of amino acids to the growing protein chain on tRNA. Ribosomes Structure It is located in two areas of the cytoplasm. Scattered in the cytoplasm. Prokaryotes have 70S ribosomes while eukaryotes have 80S ribosomes. Around 62% of ribosomes are comprised of RNA, while the rest are proteins. The structure of free and bound ribosomes is similar and is associated with protein synthesis. Ribosomes Structure Ribosome Composition A ribosome is a ribonucleoprotein complex. Comprises both RNA and protein components. Subunit Structure Consists of two subunits: smaller and larger. Smaller subunit binds and decodes mRNA. Larger subunit facilitates Ribosome Function Protein Synthesis Assembles amino acids to form essential proteins. Crucial for carrying out cellular functions. mRNA Synthesis DNA undergoes transcription to produce mRNA. mRNA is synthesized in the nucleus and transported to the cytoplasm. Ribosomal Binding Ribosomal subunits in the cytoplasm bind to mRNA polymers. tRNA molecules facilitate protein synthesis on the ribosome. Site of Protein Synthesis Ribosomes serve as the primary site for protein synthesis within the cell. Protein Utilization Proteins synthesized in the cytoplasm are used within the cytoplasm. Proteins synthesized by ribosomes bound to the endoplasmic reticulum are transported outside the cell. Centrosome “Centrosome is a micCentrosome Structurerotubule-organizi ng center in animal cells.” Centrosome Structure Centrosome Structure Composed of two perpendicular centrioles: a mother centriole and a daughter centriole. Linked together by interconnecting fibers. Surrounded by an amorphous pericentriolar matrix. Protein Complex Contains a complex of proteins that aid in the formation of additional microtubules. Essential for microtubule organization and cell division. Nucleation and Anchoring Involved in nucleation and anchoring of cytoplasmic microtubules. Critical for the structural organization of the cell.  Centrosome Structure Cell Division During cell division, one centrosome from the parent cell is transferred to each daughter cell. Centrosomes initiate division before the S-phase. Interphase Functions In proliferating cells, centrosomes organize mitotic spindles. During interphase, centrosomes arrange an astral ray of microtubules. Microtubules aid in intracellular trafficking, cell adhesion, and cell polarity. Post-Mitotic Cells In post-mitotic cells, the centrosome consists of a mature centriole (mother centriole) and an immature centriole (daughter centriole). Centrosome Production The centrosome cycle consists of four phases: 1. G1 phase where the duplication of centrosome takes place. 2. G2 phase where the centrosome maturation takes place. 3. The mitotic phase where the centrosome separation takes place. 4. A late mitotic phase where the chromosome disorientation takes place. Centrosome Function The centrosomes help in cell division. They maintain the chromosome number during cell division. They also stimulate the changes in the shape of the cell membrane by phagocytosis. In mitosis, it helps in organizing the microtubules ensuring that the centrosomes are distributed to each daughter cell. They regulate the movement of microtubules and cytoskeletal structures, thereby, facilitating changes in the shapes of the membranes of the animal Cell Cytoskeleton “Cytoskeleton is the structure that maintains the shape and internal organization of the cell, and provides it mechanical support. “ Cytoskeleton Present in eukaryotic cells, prokaryotic cells, and archaeans. Composed of a network of fibrous structures. Eukaryotic cell cytoskeleton contains protein filaments and motor proteins, forming a complex mesh within the cell. Provides structural shape and support to the cell. Organizes organelles within the cell. Facilitates the intracellular transport of molecules. Essential for cell division processes. Participates in cell signaling pathways. Cytoskeleton Structure A cytoskeleton structure comprises the following types of fibers: Microfilaments Microtubules Intermediate Filaments  Cytoskeleton Structure Microtubules Microtubules are small, hollow, round tubes with a diameter of about 24 nanometers. Composed of tubulin, a protein. Thirteen tubulins link together to form a single microtubule. Microtubules are highly dynamic, and capable of rapid changes. They can continuously grow or shrink. Transporting cellular materials. Facilitating the division of chromosomes during cell division. Cytoskeleton Structure Microfilaments Thread-like protein fibers, 3-6 nm in diameter. Composed of the protein actin. Responsible for muscle contraction, found in muscle cells. Play a role in various cellular movements, including cytokinesis, contraction, and gliding. Cytoskeleton Structure Intermediate Filaments Diameter: About 10 nm. Provide tensile strength to the cell. Facilitate the formation of keratins and neurofilaments.  Cytoskeleton Structure The cytoskeleton is also made up of certain motor proteins. These include: Kinesin These proteins move along the microtubules carrying the cellular components. They pull the organelles along the cell membrane. Dyneins These pull the cell organelles towards the nucleus. Myosin These interact with actin protein and are responsible for muscle contractions. They also perform cytokinesis, exocytosis, and endocytosis. Cytoskeleton Function 1.It provides shape and support to the cell. 2.It helps in the formation of vacuoles. 3.It holds different cell organelles in place. 4.It assists in cell signalling. 5.It supports intracellular movements like the migration of cell organelles, transportation of vesicles in and out of the cell, etc. Plasma Membrane Outermost envelope-like membrane surrounding the cell and its organelles. Also known as the phospholipid bilayer. Present in both prokaryotic and eukaryotic cells. Functions as a boundary. Selectively permeable, regulating the entry and exit of specific substances. Acts as a connecting system, facilitating communication between the cell and its environment. Plasma Membrane Structure Composed of carbohydrates, phospholipids, proteins, and conjugated molecules. Thickness ranges from 5 to 8 nanometers. Structure Flexible, lipid bilayer surrounding and containing the cell's cytoplasm. Described as the fluid mosaic model based on molecular arrangement. Plasma Membrane Structure Fluid Mosaic Model Proposed in 1972 by biologists Garth L. Nicolson and Seymour Jonathan Singer. Explains the detailed structure of the plasma membrane in eukaryotic cells. Components such as phospholipids, proteins, carbohydrates, and cholesterol create a fluid appearance in the plasma membrane.  Plasma Membrane Function The plasma membrane functions as a physical barrier between the external environment and the inner cell organelles. The plasma membrane is a selectively permeable membrane, which permits the movement of only certain molecules both in and out of the cell. The plasma membranes play an important role in both the endocytosis and exocytosis processes. The plasma membrane also functions by facilitating communication and signaling between the cells. The plasma membrane plays a vital role in anchoring the cytoskeleton to provide shape to the cell and also maintain the cell potential. References Miller S.A. and Tupper, T.A. 2019. Zoology. McGraw-Hill. New York. Samberg, E. 2018.Vertebrate Zoology.Syrawood Publishing House. New York, NY Prasad, S.N and Kashyap.2011. A Textbook of th Veterbrate Zoology. 14 Ed. New Age Publishers. New Delhi