LIFE102 Week 5 Notes
LIFE102 Week 5 Notes Life 102
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This 8 page Class Notes was uploaded by Sydney Dingman on Friday February 19, 2016. The Class Notes belongs to Life 102 at Colorado State University taught by Erik N Arthun in Winter 2016. Since its upload, it has received 23 views. For similar materials see Attributes of Living Systems in Biology at Colorado State University.
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Date Created: 02/19/16
Week 5 LIFE 102 Notes 2/15/16, Chapter 7: Membrane Structure and Function… MARCH 7, NEXT TEST Structure of membranes is more fluid than we would expect and is very, very thin. Cells & Organelles are surrounded by membranes o Molecules can move in and out of the cell, and separates the inside from the outside environments o Selectively permeable: some substances cross easily, others don’t Cellular membranes are fluid mosaics of lipids and proteins o Form by themselves because they are amphipathic Membrane structure o Myseal, the phospholipids will form a sphere by themselves because of the amphipathic tendencies. Lipids move freely in the plasma membrane o Multiple factors determine whether the membrane is fluid or viscous Fluid: liquid Viscous: gummy o Temperature Phospholipids can move side to side easily, but not switch up to down easily. High temperature will move side to side quickly Cold temperature will not move as much o Type of phospholipids More saturated fatty acids means more viscosity Less saturated fatty acids makes the phospholipids not pack together as tightly which makes it more fluid o Cholesterol content In the bilayer Acts as a fluidity buffer High temperatures, moderates the movement of the phospholipids Lower temperatures, moderates the packing of the phospholipids Freeze Fracture o When you freeze the cell then chop the membrane in half o Lots of proteins on in the bilayer Phospholipid bilayer is embedded with proteins o Peripherals- bound to membrane surface o Integrals- incorporated into membrane Integral Membrane Protein o In the proteins, hydrophobic ones will hang out inside the structure of the bilayer, hydrophilic ones hang out outside the structure of the bilayer Membrane proteins and lipids are synthesized in the ER and Golgi o Proteins determine most of the membrane’s specific functions o Some proteins will be released, while other embed with the phospholipid bilayer Membrane Protein Functions o Transport Help move molecules from one side to the other Channel proteins: specific doorways through which molecules can get through the hydrophobic interior Carrier o Enzyme Activity Help with chemical reactions and can be grouped into metabolic pathways Modifies protein in some way so that it is more usable. o Signal transduction Send chemical messages across the membrane How cells communicate with other cells or their environment o Cell-Cell recognition 2 Glycoproteins in membrane serve as identification Blood Types o Intercellular joining Bind cells together Tight junctions Gap junctions o Cytoskeleton & extracellular matrix attachments Helps maintain cell shape and location of proteins Why do cells require movement across their membranes? o Metabolic needs: Nutrients and oxygen in Wastes and carbon dioxide out o Maintain potential energy of the cell: Inorganic ions in and out How are molecules moved across membranes? o Not all substances cross the same o Passive transport requires no energy o Active energy requires a little bit of ATP energy o Some go straight through the bilayer o Others need to go through a channel or carrier protein Passive transport o No additional energy used to move the substance from high to low concentration o Concentration gradient: things move from high to low concentrations for free o Can move through in 3 ways: Lipid bilayer Channel proteins Carrier proteins o Charged molecules and polar molecules need some sort of channel to move through the bilayer 3 o Occurs by diffusion: the movement of molecules from where there is a lot of them to where there is few of them o Molecules tend to spread out evenly Active transport o Uses additional energy to pump energy from a low concentration to a high concentration. 2/17/16, Chapter 7 cont. Molecules that can diffuse across lipid bilayers (without help of proteins): o Non-polar molecules o Small, uncharged polar molecules Larger polar molecules and ions need transport proteins to get across membrane Osmosis o Passive diffusion of water across a selectively permeable membrane o Tonicity: the ability of a surrounding solution to cause a cell to gain or lose water o Hypotonic: solute concentration is less than that inside the cell; cell gains water o Hypertonic: solute concentration is greater than that inside the cell; cell loses water o Isotonic: solute concentration is the same as that inside the cell; no net water movement across the plasma membrane o Water follows salt What drives osmosis? o Solutes that don’t cross the membrane o Water diffuses Towards the highest solute concentration Towards lowest free water concentration Implications of osmosis for cells o Animal cells prefer an isotonic environment o Plant cells prefer a hypotonic environment 4 Facilitated diffusion through proteins o Channel proteins Specific hydrophilic tunnel across membrane o Carrier proteins Pass specific substances down in concentration gradients through changes in the shape of the membrane protein Shift their binding site across the membrane o Faster than diffusion across the plasma membrane o Ions and large polar molecules can cross the membrane Active transport o Moves molecules against concentration gradient (requites ATP energy) o ATP’s terminal phosphate is transferred to the membrane protein o Induces change in protein shape, moving molecule across membrane o Sodium potassium pump: pumps 3 Na+ out and Pumps 2 K+ in Active transport through protein ion pumps creates a membrane potential o Membrane potential: voltage difference across a membrane generated by ion pump o Create electrochemical gradients o 2 forces act on ions: Chemical force: ion’s concentration gradient Electrical force: effect of membrane potential on ions movement Active and passive transport may be coupled through a cotransporter o The gradient created by the active transport of one molecule can move a second molecule up its concentration gradient o “Cotransporter”: transport of two different molecules at the same time by one carrier o Plants: load glucose into the veins of leaves o Animals: Na+/Glucose cotransporter keeps Na levels up Transport of particles/large molecules 5 o Proteins, polysaccharides, complex particles o Packaged in vesicles o Exocytosis: secretion of vesicle content via fusion with membrane o Endocytosis: Captures content from outside of the cell o Phagocytosis: cell engulfs a particle and forms food vacuole, which is digested by a lysosome o Pinocytosis: cell captures extracellular fluid (which contains dissolved solutes) o Receptor Mediated Endocytosis: cell acquires a specific substance that is found in low abundance 2/19/16, Chapter 8, Metabolism Metabolism: all biochemical reactions that occur in cells o Transformation of matter and energy Catabolism and Anabolism o Anabolism: any process that results in synthesis or assembly of large molecules from smaller molecules Usually requires the input of energy Synthesis of proteins from amino acids o Catabolism: the breakdown of large molecules into smaller molecules Involves breakage of chemical bonds Often releases energy Cellular respiration o Catabolism produces energy used in anabolism, you can rarely have one without the other Energy: the capacity to cause change (rearrange matter, physically move or change bonds) o Potential energy: energy provided by location or structure o Kinetic energy: energy of motion o Chemical energy: potential energy in chemical bonds, released in chemical reactions First Law of Thermodynamics 6 o Law of Energy Conservation Energy can be transferred and transformed to other forms of energy, but it cannot be created or destroyed Plants transform light energy chemical energy The energy of the universe is constant Energy needed for anabolic reaction = energy released in catabolic reaction Second Law of Thermodynamics o During every energy transfer or transformation, some energy is unusable and is often lost as heat o All energy transformations result in an increase of disorder o Afterwards, there is less “useful” energy o Useful energy= “Gibbs free energy” o Implications for metabolism: spontaneous reactions are only possible if the free energy (G) decreases Only process with a negative change in G are spontaneous o Exergonic and Endergonic Reactions in Metabolism An exergonic reaction proceeds with a net release of free energy and is spontaneous An endergonic reaction absorbs free energy from its surroundings and nonspontaneous o Amount of energy needed to let a reaction proceed: free (Gibbs) energy change, G If G < 0: exergonic reaction If G > 0: endergonic reaction ATP’s Role in Metabolism o In cells: energy from exergonic reactions is used to fuel endergonic reactions o We use our catabolism (to breakdown glucose into ATP), we store the ATP and use it in anabolic reactions (Look at graphic on slide 15 of PowerPoint) o ATP: adenosine triphosphate: molecule that transfers energy from exergonic to endergonic reactions 7 o Made of Adenine+Ribose+3 phosphate groups (negative charges on each phosphate group pushing against each other, creating energy) How ATP transfers energy o Hydrolysis of ATP Water is added to it and the third phosphate is removed, releasing energy ATP Role in Metabolism o ATP gives P to reactant (G>0) o Reactant is energized o Reaction can proceed (G<0) ATP and Metabolism o ATP is needed for most endergonic processes and has to be created constantly o ATP is produced through respiration: breakdown of C compounds to CO2 and H2O o See slide 19 on Chapter 8 PowerPoint on Canvas 8
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