Life 102, Week 5 Notes
Life 102, Week 5 Notes Life 102
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This 8 page Class Notes was uploaded by Kyra Ferguson on Sunday February 21, 2016. The Class Notes belongs to Life 102 at Colorado State University taught by Erik Arthun in Winter 2016. Since its upload, it has received 18 views. For similar materials see Attributes of Living Systems in Life Science at Colorado State University.
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Date Created: 02/21/16
Chapter 7: Membrane Structure and Function Cells and organelles are surrounded by membranes that are selectively permeable. Most realistic version of the cell is the Fluid Mosaic Model. The phospholipid bilayer is very fluid The proteins in the membrane give it most of its function. Cellular membranes are "fluid mosiacs" of lipids and proteins phosholipids- most abundant lipid in the plasma membrane phospholipids are amphipathic, containing hydrophobic and hydrophillic Membrane structure polar phosphate head and nonpolar fatty acid tails Functions: o create boundaries o control traffic selectively permeable Lipids more freely in the plasma membrane Multiple factors determine whether the membrane is fluid (liquid) or viscous (gummy) o temperature o type of phospholipids o cholesterol Fluidity of Membrane can move side to side (10 times per second) flip flop (once per month) Type of hydrocarbon tails in phospholipids Unsaturated or Saturated Affects fluidity Fluid (unsaturated, like oil), viscous (saturated) Steroid cholesterol keeps membrane fluidity optimal at different temperatures moderate temps- reduces phospholipid movement, reducing fluidity low temps- disrupts the regular packing of phospholipids, hindering solution Phospholipid bilayer is embedded with proteins (50% by weight) Freeze Fracture shows that proteins are embedded with proteins peripherals- bound to membrane surface integrals- transmembrane; membrane proteins "float" freely in the lipids nonpolar amino acids (in the nonpolar region the lipids) Membrane proteins and lipids are synthesized in the ER and Golgi Proteins determine most of the membrane's specific functions. Membrane protein functions transport- help move molecules from one side to another channel vs carrier enzyme activity- help with chemical reactions, and can be grouped into metabolic pathways signal transduction- send chemical messages across the membrane cell-cell recognition glycoproteins in membrane serve as identification ie, blood type- more than 50 on a blood cell Why do cells require movement across their membranes? Metabolic needs o Nutrients and Oxygen in o Wastes and Carbon Dioxide out Maintain potential energy of the cell: o Inorganic ions in and out o H , Na , K , Ca+ How are molecules moved across membranes? Passive o Always via "diffusion" - molecules move from high to low concentrations, and spread out evenly o Different molecules diffuse independently o Requires no addition of energy o Through bilayer Lipid- nonpolar o Through a transport protein (channel and carrier) Transport- polar or charged Active o Requires energy in the form of ATP o Molecules move against concentration gradient Molecules that can diffuse across lipid bilayer Nonpolar molecules o ie O2, CO2, hydrocarbons Small, uncharged polar molecules o ie H2O Larger molecules and ions need transport proteins to get across membrane Osmosis- passive diffusion of water across selectively permeable membrane What drives osmosis? Water follows salt (dissolved substance, solutes) Solutes that don't cross the membrane Water diffuses towards highest solute concentration Towards lowest free water concentration Direction of water movement during osmosis Both number of particles and water concentration have effects Molarity is additive (.1 glucose _+.4 fructose > .4 glucose) Water Balance of Cells without walls Tonicity is the ability of a surounding solution to cause a cell to gain or lose water Isotonic solution- solute concentration is the same as that inside the cell; no net change Hypertonic- solute concentration is more than that inside the cell; cell loses water Hypotonic- solute concentration is less than that inside the cell, cell gains water Implications of Osmosis for cells Animal Cells Animal cells prefer an isotonic environment Shrivels in hypertonic solutions Explodes in hypotonic solution Plant Cells Prefer hypotonic environment Becomes plasmolyzed in hypertonic solution (wilts) Becomes flaccid in isotonic solution Facilitated Diffusion Through Proteins Channel o specific hydrophilic tunnel across the membrane o ie aquaporins (water channels) serve to retain water in your kidneys without it, you would excrete 180 L of water a day Carrier o pass specific substances down concentration gradients through changes in the hsape of membrane protein o shift their binding site (translocate) across the membrane unbound- open to one side of the membrane bound- the other side (when it bonds to molecule) o substance is released Faster than diffusion across plasma membrane ions and large polar molecules can cross the membranes Active Transport Through Proteins Moves molecules against concentration gradient (requires ATP energy) ATP's thermal phosphate is transferred to membrane protein Induces change in protein shape Ion pumps create a membrane potential Membrane potential voltage difference across a membrane, generated by ion pumps Create electrochemical gradients 2 forces act on ions: Chemical: ions concentration gradient Electrical: effect of membrane potential on ion's movement Coupled through a cotransporter "Cotransporter"- transporter of two different molecules at the same trie by one carrier Transport of Particles/Large Molecules Proteins, Polysaccharides, Complex particles (Packaged in vesicles) Exocytosis- secretion of vesicles content via fusion with membrane Endocytosis- captures content from outside the cell Phagocytosis- Cell engulfs a particle and forms food vacuoles, which is digested by a lysosome Pinocytosis- cell captures extracellular fluid (which contains dissolved solutes) o non-specific Receptor Meditated- Cell acquires a specific substance found in low abundance, receptors are recycled Chapter 8: Introduction to Metabolism Metabolism- all biochemical reactions that occur in cells transformation of matter and energy Catabolism- breakdown of large molecules into smaller molecules o involves breakage of chemical bonds o often releases energy o ie, Cellular Respiration Anabolism- any process that results in synthesis or assembly of large molecules from smaller molecules o usually requires input of energy o ie synthesis of proteins of amino acids Energy- the capacity to cause change ie, rearrange matter, physically move or change bonds ie Potential Energy- Energy provided by location or structure ie Kinetic Energy- energy of motion ie Chemical Energy- potential energy of chemical bonds, released in chemical reactions First Law of Thermodynamics (Law of Energy Conservation) Energy can by transferred or transformed to other forms of energy but cannot be created or destroy Laws dictate metabolism, which require input or output of energy ie, Plants transform light into chemical energy All energy in the universe is constant Second Law of Thermodynamics During every energy transfer of transformation, some energy is unusable, and is often lost as heat The universe tends to go from highly ordered and complicated to disordered and less complicated All energy transformations result in an increase of "disorder" (entropy) Afterwards there is less "useful" energy Useful energy- "Gibbs free energy" Implications of metabolism: o Spontaneous reactions are only possible if the free energy (G) decreases, such as with gravitational motion, diffusion, or chemical reaction Exergonic and Endogonic Reactions in Metabolism an exergonic reaction proceeds with a net release of free energy and is spontaneous an endogonic reaction- absorbs free energy from its surroundings and is nonspontaneous If a reaction costs energy, it is endogenic, and the ∆G is greater than 0 If a reaction releases energy, it is exergonic, and the ∆G is less than 0 ATP's role in metabolism: ATP (adenosine triphosophates): molecule that transfers energy from exergonic to energonic reactions The energy shuttle fo the cell Adenine + Ribose + 3 Phosphate groups In cells: Energy from exergonic reactions is used to fuel endogonic reactions Mechanism of ATP Energy Transfer ATP ↔ ADP + P + energy The third phosphoate is removed All 3 phosphates have a negative charge, they are pushing a bunch against each other, which holds a lot of chemical energy (like a spring) ATP gives P to reactant, and reactant is energized
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