Cell Biology PowerPoint Presentation

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Cell Biology

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Outline Cell Structure and Organelles Cell Molecular Components Water and Chemical properties Cell Membrane Osmotic Properties of cells Cell molecule transportation

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Prokaryotes and Eukaryotes

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Structure of Animal Cells

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Cell Organelles Nucleus 1 Nuclear envelope Chromatin and DNA Nucleolus Mitochondria Double membrane Mitochondrial (maternal) DNA “Power House” of the cell Food converted into energy Adenosine triphosphate (ATP) Consumes Oxygen, produces CO2

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What is ATP? Nucleotides “Carry” chemical energy from easily hydrolyzed phosphoanhydride bonds Combine to form coenzymes (coenzyme A (CoA) Used as signaling molecules (cyclic AMP)

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Cell Organelles Endoplasmic Reticulum Site where cell membrane and exported material is made Ribosomes (rough) Make protiens Smooth ER- lipids Golgi Apparatus Receives and modifies Directs new materials Lysosomes Intracellular digestion Releases nutrients Breakdown of waste

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Cell Organelles Peroxisomes Hydrogen Peroxide generated and degraded Cytosol Water based gel Chemical reactions Cytoskeleton Filaments (actin, intermediate and microtubules) Movement of organelles and cell Structure/strengthen cell Vessicles Material transport Membrane, ER, Golgi derived vessicles

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Organic Molecules of Cells Proteins Carbohydrates Lipids Nucleic acids

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Proteins Most diverse and complex macromolecules in the cell Used for structure, function and information Made of linearly arranged amino acid residues “folded” up with “active” regions

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Types of Proteins 1) Enzymes – catalyzes covalent bond breakage or formation 2) Structural – collagen, elastin, keratin, etc. 3) Motility – actin, myosin, tubulin, etc. 4) Regulatory – bind to DNA to switch genes on or off 5) Storage – ovalbumin, casein, etc. 6) Hormonal – insulin, nerve growth factor (NGF), etc. 7) Receptors – hormone and neurotransmitter receptors 8) Transport – carries small molecules or irons 9) Special purpose proteins – green fluorescent protein, etc.

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Humans have around 30,000 genes. Each cell has the full set of the human genes but only makes specific protein. Why? Implication in tissue engineering

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Hydrophobic molecules Energy storage, membrane components, signal molecules Triglycerides (fat), phospholipids, waxes, sterols Lipids Sugars, storage (glycogen, starch), Structural polymers (cellulose and chitin) Major substrates of energy metabolism Carbohydrates

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Nucleic Acids DNA (deoxyribonucleic acid) and RNA encode genetic information for synthesis of all proteins Blue print

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Water Molecule Polarity of H2O allows H bonding Water disassociates into H+ and OH- Imbalance of H+ and OH- give rise to “acids and bases” - Measured by the pH pH influence charges of amino acid groups on protein, causing a specific activity Buffering systems maintain intracellular and extracellular pH

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Hydrophobic “Water-fearing” Molecule is not polar, cannot form H bonds and is “repelled” from water Insoluble Hydrophillic “Water-loving” Molecule is polar, forms H bonds with water Soluble Water Molecule

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Cell Membrane

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Cell Membrane Composition Plasma membrane encloses cell and cell organelles Made of hydrophobic and hydrophillic components Semi-permeable and fluid-like “lipid bilayer”

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Integral proteins interact with “lipid bilayer” Passive transport pores and channels Active transport pumps and carriers Membrane-linked enzymes, receptors and transducers Sterols stabilize the lipid bilayer Cholesterol Cell Membrane Composition

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Lipid Molecules

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Osmosis (Greek, osmos “to push”) Movement of water down its concentration gradient Hydrostatic pressure Movement of water causes fluid mechanical pressure Pressure gradient across a semi-permeable membrane Osmotic Properties of Cells

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Hydrostatic Pressure

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Donnan Equilibrium Semi-permeable membrane Deionized water Add Ions Balanced charges among both sides

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Add anion More Cl- leaves I to balance charges Donnan Equilibrium Diffusion

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Ionic Steady State Potaasium cations most abundant inside the cell Chloride anions ions most abundant outside the cell Sodium cations most abundant outside the cell

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Donnan Equilibrium [K+]i [K+]ii [Cl-]ii [Cl-]i =

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Erythrocyte Cell Equilibrium No osmotic pressure - cell is in an isotonic solution - Water does not cross membrane Increased [Osmotic] in cytoplasm - cell is in an hypotonic solution - Water enters cell, swelling Decreased [Osmotic] in cytoplasm - cell is in an hypotonic solution - Water leaves cell, shrinking

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Cell Lysis Using hypotonic solution Or interfering with Na+ equilibrium causes cells to burst This can be used to researchers’ advantage when isolating cells

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Molecules Related to Cell Permeability Depends on Molecules size (electrolytes more permeable) Polarity (hydrophillic) Charge (anion vs. cation) Water vs. lipid solubility

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Cell Permeability Passive transport is carrier mediated Facilitated diffusion Solute molecule combines with a “carrier” or transporter Electrochemical gradients determines the direction Integral membrane proteins form channels

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Crossing the Membrane Simple or passive diffusion Passive transport Channels or pores Facilitated transport Assisted by membrane-floating proteins Active transport pumps and carriers ATP is required Enzymes and reactions may be required

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Modes of Transport

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Carrier-Mediated Transport Integral protein binds to the solute and undergo a conformational change to transport the solute across the membrane T

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Channel Mediated Transport Proteins form aqueous pores allowing specific solutes to pass across the membrane Allow much faster transport than carrier proteins

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Coupled Transport Some solutes “go along for the ride” with a carrier protien or an ionophore Can also be a Channel coupled transport

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Three main mechanisms: coupled carriers: a solute is driven uphill compensated by a different solute being transported downhill (secondary) ATP-driven pump: uphill transport is powered by ATP hydrolysis (primary) Light-driven pump: uphill transport is powered by energy from photons (bacteriorhodopsin) Active Transport

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Active Transport Energy is required

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Against their electrochemical gradients For every 3 ATP, 3 Na+ out, 2 K+ in Na+/K+ Pump Actively transport Na+ out of the cell and K+ into the cell

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Na+ exchange (symport) is also used in epithelial cells in the gut to drive the absorption of glucose from the lumen, and eventually into the bloodstream (by passive transport) Na+/K+ Pump

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About 1/3 of ATP in an animal cell is used to power sodium-potassium pumps Na+/K+ Pump In electrically active nerve cells, which use Na+ and K+ gradients to propagate electrical signals, up to 2/3 of the ATP is used to power these pumps

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Endocytosis and Exocytosis Exocytosis - membrane vesicle fuses with cell membrane, releases enclosed material to extracellular space. Endocytosis - cell membrane invaginates, pinches in, creates vesicle enclosing contents

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Receptor Mediated Endocytosis

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The Cytoskeleton • The cytoskeleton, a component of structural functions, is critical to cell motility. • Cells have three types of filaments that are distinguishable by the diameter. • Actin filaments (microfilaments): 5-9 nm diameter with twisted strands.

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Microtubules: hollow tube-like structure ~ 24 nm diameter Intermediate Filaments: 9-nm diameter

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Cell Locomotion Why do we care about cell locomotion? Host defense Angiogenesis Wound healing Cancer metastasis Tissue engineering Steps: Protrusion Adhesion Traction

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External signals must dictate the direction of cell migration. Cell migration is initiated by the formation of large membrane protrusion. Video microscopy showed that G-actin polymerizes to F-actin. (Drugs can alter this process). Actin exists as a globular monomer (G-actin) and; A filamentous polymer (F-actin) protein. The addition of Mg2+, K+ or Na+ to a solution of G-actin induces the formation of F-actin and this process is reversible. Elastic mechanical property of actin filament.

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