GNHIS_LEC 2_ The Cell PDF

THE CELL They are the basic structural & functional units of all multicellular organisms. All living organisms have many cell types, whose main function is to maintain homeostasis. Two components: 1. All organisms are composed of cells. 2. Cells only come from pre-existing cells. Base...

THE CELL They are the basic structural & functional units of all multicellular organisms. All living organisms have many cell types, whose main function is to maintain homeostasis. Two components: 1. All organisms are composed of cells. 2. Cells only come from pre-existing cells. Based on function: 1. Somatic cells: building blocks of an organism's body. 2. Sex cells: organism’s reproductive cells. Based on the way DNA is stored: 1. Prokaryotic cells. 2. Eukaryotic cells. Prokaryotes Eukaryotes No nucleus Have nucleus Have cell walls made of peptidoglycan Cell walls if present, made of cellulose (chitin in fugi) No membrane bound organelles Has membrane bound organelles (compartmentalization) Have pili & fimbriae (adhesion) & flagella (propulsion) Have cilia/flagella (movement) Mucilaginous capsule No mucilaginous capsule present Size ranges from 0.5 to 100um Size ranges from 10 to 150um Animal cells Plant cells Generally small Larger than animal cells Cell wall is absent Their plasma membrane is surrounded by a rigid cell wall of cellulose Except protozoan euglena, no animal cell possesses Plastids are present plastids Vacuoles are many and small Most mature plant cells have a larger central sap vacuole Single highly golgi complex Have simpler units and prominent golgi complex (dictyosomes) Have centrosome & centrioles Lack centrosome & centrioles  Common features: 1. Cell membrane: barrier/boundary between internal & external environment. 2. Cytoplasm: contains the organelles. 3. Organelles: small structures that carry out various functions within the cell. - Cell membrane Separate the inside of cell from the outside Selective barrier Provides the size & shape of the cell Helps in cellular communication - Layers of cell membrane A. Mucopolysaccharide/carbohydrate layer B. Outer protein Antigen Receptor site C. Lipid bilayer: Has a fluid consistency, therefore the compositional structure of the cell membrane is characterized by fluid mosaic model. Has a two layers (polar head are arranged on both inner surfaces of cell membrane, and nonpolar tails face each other in the center of the membrane) Phospholipid Cholesterol Glycolipid D. Inner protein layer Channels/pores Transporters A. Cilia: short hair-like projections from the cell surface, move fluids along cell surface B. Flagella: longer than cilia, moves the entire cell, only example is the sperm cell’s tail. General rule: - There is 1 nucleus in one cell except RBC & platelets - Muscles are multinucleated Oval, round, elliptical, usually centrally located It is membrane-encapsulated structure containing various materials especially the genetic material of the cell (DNA) Fxn: directs, orders and regulates all metabolic activities of the cell Chromosomes: - Contains thousands of hereditary units called genes - Each chromosomes consists single molecule of DNA & associated packing proteins.  Parts of nucleus: a. Nucleolus - small, discrete, round basophilic body (rich RNA) - FXN: Regulate the rate of cell division, site of ribosome synthesis b. Nuclear envelope - Double membrane b/n the nucleus and the cytoplasm - Outer membrane - Inner membrane c. Nuclear pore - Opening embedded with protein - Regulates passage into and out of the nucleus Contains all cellular contents between cell membrane & nucleus Cytosol-fluid portion (mostly water) Organelles - subcellular structure embedded in cytosol, having characteristic shapes and specific fxns. Network of protein filaments throughout the cytosol Fxn; provide structural support for the cells 1. Filament: a. Microfilaments: flexible chains of actin molecules b. Intermediate filaments: ropelike fibers formed from variety of proteins 2. Microtubules: Continuously elongate and shorten a property referred to as dynamic stability Very small rounded bodies found on both ends of the nucleus Contains centriole FXN: regulation An organelle of cells that forms a network of membranes in the shape of flattened sacs or tubules Two types: Rough ER & Smooth ER - Rough ER: connected to the nuclear envelope, series of flattened sacs, surfaced with ribosomes, FXN: produces various proteins. - Smooth ER: a network of membrane tubules, does not have ribosomes, FXN: synthesizes fatty acids and steroids, detoxifies certain drugs. Made up of protein and rRNA Bound-found on the surface of rough ER Unbound-float freely within cytoplasm Composed of large and small sub-units: - Prokaryotes: 80s (60s + 40s) - Eukaryotes: 70s (50s + 30s) Site of protein synthesis  Barrel-shaped organelle made of enzyme Cuts protein molecules apart Consists of 3-20 flattened membranous sacs called “cisternae” FXN: primary site for packaging cellular secretion Vesicles that form from the golgi complex Contains powerful enzymes FXN: breakdown cellular waste, debris, and nutrients for use of the cell Mechanism: - Autography - Heterography Smaller than lysosomes Detoxify several toxic substances such as alcohol Abundant in liver Spherical-shaped membrane-bound sacs Contain various types of materials to be transported through the cell FXN: transport cellular material Double membrane-bound organelles containing circular strand of DNA Powerhouse of the cell FXN: generate ATP More prevalent in physiologically active cells: muscles, liver, and kidneys Contains own DNA Parts: - Cristae: series of folds in the inner membrane - Matrix: large central fluid-filled cavity Aggregates of specific types of molecules Primarily storage sites A. Passive transport Movement of substances down to concentrated gradient due to the kinetic energy of the substance NO ATP Types of passive transport: a. Simple diffusion - Unassisted net movement solute particle through the plasma membrane - Lipid soluble: fats, fat-soluble vitamins, oxygen, carbon dioxide - Small molecules: ions such as chloride  b. Facilitated/facultative diffusion - No need ATP (follow the concentration gradient) - Needs specific carrier proteins - Difficulty in moving substances against gradient c. Osmosis - Diffusion of water across a selectively permeable membrane - Movement of solvent from a region of lesser concentrated solution to a greater solute concentration B. Active transport Movement of molecules from an area of lesser concentration to an area of higher concentration Requires ATP Requires specific carrier CHONS C. Vesicular transport Vesicle formed or lost as material is brought into a cell or released from a cell Types of vesicular transport 1. Endocytosis: Performs the uptake and transfer of molecules and solids across the cell membrane into the cell interior 2. Exocytosis: Process of releasing material from the cell cytoplasm, across the cell membrane to the exterior 3. Pinocytosis: Process by which cells ingest small molecules of extracellular fluids or liquids 4. Phagocytosis: Ingestion or intake of large solid particles, such as worn-out cells, or cellular debris, by specialized cells. Adhesion junction: form sturdy flexible sheets of cells Tight junction: membrane protein of adjoining cells can attach together to form tight junctions Gap junction: form when plasma membrane channels form two different cells join together.