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9/17/12Chapter 6: The Cell Membrane Functions Regular passage of materials in and out of the cell Receptor proteins – receive info from outside the cell Maintains structural and chemical relationships with neighboring cells Cell recognition Self vs. Non-self- Example : Organ transplant rejection Protects the cell, Allows movement, Involved in secretion Structure Fluid-Mosaic Model of the cell membrane Amphipathic – molecule with a hydrophobic and a hydrophilic region Example : proteins*Cell Fusion Experiment Membrane protein diversity Channel protein (trans-membrane protein) Allows particular molecules or ions to pass into and out of the cell Carrier protein – Active transport Selectively interacts with specific molecules or ions “Pumps” materials across the membrane by using energy → ATP Cell recognition protein Identifies the cell Glycoproteins Receptor proteins Signal transduction- Molecule, such as a hormone, will bind to the receptor site Enzymatic protein Catalyze a reaction Substrate binds to an enzyme → causes some reaction in the cell Anchor protein Anchors the cell Inter-cellular junctions Attach membranes of adjacent cells*Freeze Fracture Technique-Method for studying membranes-Take liquid nitrogen frozen membranes-Breaks open, leaving portions of membrane exposed-Displays proteins embedded in phospholipid bilayer9/17/12 Cell Walls Found in plants, algae, bacteria, fungi Contain lignin – rigid fibers Made up of cellulose  Made up of pectin Involved in “wound healing”Passage of Materials through Membranes Membrane structure Polar won’t pass through very easily Size of molecule Charge of molecule Permeable : substances will pass through Impermeable : substances will not pass through Semi-permeable : some substances will pass through and some substances will not All biological membranes are semi-permeable Diffusion Movement of material (solute) from high concentration to low concentration in order to establish an equilibrium Rate of diffusion  Increase temperature → increase rate of diffusion Size of molecule Shape of molecule Charge of molecule Brownian movement Random movement of particles (molecules) due to their kinetic energy Dialysis Diffusion of a solute through a selectively permeable membrane Facilitated Diffusion Moves glucose Uses carrier proteins Cell membrane is impermeable to polar molecules Must have concentration gradient for any type of diffusion to occur Carrier molecules (proteins) are passive conveyor belts- No ATP required- GLUCOSE → glucose [Big concentrations → little concentrations] Osmosis Diffusion of water through a semi-permeable membrane Aquaporins (water holes) Channel proteins Isotonic9/17/12 Equilibrium between solutions Hypertonic Movement of water out of the cell  Higher concentration of water inside the cell Cell shrinks Hypotonic (Hippo) Movement of water into the cell Higher concentration of water outside of the cell Cell expands / swells Active Transport Sodium Potassium Pump Aka Sodium Potassium ATPase- Enzyme Moves 3 Na+ out while moving 2 K+ in- Creates charge separation → results in inside of cell being more negative Membrane Potential- Cell is negative- 3 out for every 2 in Co Transport The concentration gradient of K+ is used to move other substances (x) against its concentration gradient- (x) is moving from low concentrations to high concentrations Requires energy Cell Signaling Receptor proteins  Signal transduction Convert and amplify an extracellular signal into an intracellular signal Hormone – first messenger Hormone → Receptor protein → G protein → Adenylyl cyclase → ATP → Cyclic AMP → protein kinases → metabolic and structural changes in the cell Cyclic AMP – second messenger cAMP activates a bunch of enzymes called protein kinases Endocytosis and Exocytosis Exocytosis : Cell ejects waste products Endocytosis  Phagocytosis : Cell eating Pinocytosis : Cell drinking Receptor mediated endocytosis Lymphocytes → specific kind of cell eating Cell Junctions and Communication Desmosomes Join two cells together9/17/12 Button-like Allow movement of substances in the intracellular space  Tight Junctions Impermeable connections between cells Membrane fused together Gap Junctions Channel between 2 cells Energy and Metabolism Energy Flow Metabolism : the sum of all chemical reactions that take place within an organism Energy : the ability to produce a change in the state or motion of matter3 Major Processes Photosynthesis Step by step process of creating glucose and oxygen through the chemical reactions of the intake of carbon dioxide and water Cellular Respiration Step by step break down of glucose (starch) → which results in the production of energy rich phosphate bonds ATP Cellular Work Chemical energy of ATP is utilized by the cell to do work → muscle contraction, active transport, synthesize new moleculesCertain Principles that Govern all Energy Transformations-No such thing as a 100% effective machine Thermodynamics Study of energy Joules/Calories Exothermic process Energy released to the environment Endothermic process Reaction → energy is absorbed from the environment 1st law of thermodynamics Energy cannot be created or destroyed, it just changes form 2nd law of thermodynamics All energy transformations result in the loss of some energy and it is unrecoverable ATP → ADP + P [energy (work)] Entropy – energy lost (heat)9/17/12 The measure of the disorder of a system Perpetual Motron Machine Violates the 2nd law of thermodynamics Gibbs Free Energy Energy available to do work ∆G Exergonic Reaction -∆G Reactants (ATP) → activation energy → products (ADP+P) [High, Rise, Low] Can occur spontaneously Release free energy Perform work Endergonic Reactions +∆G Reactants (amino acids) → activation energy → products (proteins) [Low, Rise, High] Absorbs energy from the environment Biosynthetic reactions ∆G = ∆H - T∆S(Gibbs Free Energy = Total Energy Stored – Temperature × Entropy)*Biological Systems are able to trap

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Ole Miss BISC 160 - Chapter 6: The Cell Membrane

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