Bio 151 1nd Edition Lecture 4 Outline of Last Lecture - Nucleic acids- The cell theory- Biological Membranes –Structureo Major components (95%) Phospholipids, proteins Models of organizationo Minor components (5%) Glycoproteins and glycolipids (cell identify markers) Sterols (fluidity buffers)Outline of Current Lecture - Membrane Fluidity- Membrane Transporto Transport proteinso Energy Requirements Passive and Active Transporto Coupling mechanismsCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Membrane Fluidity depends on lipid structure: o Phospholipids aren’t bonded, can move all over No restriction on movement As fluid as salad dressing Membranes have to be this fluid in order to worko Living organisms need to change lipids to maintain fluidity as temperature changes- Strategies organisms use to increase fluidity when temperature decreaseso Increase degree of unsaturation in lipids Increase number of unsaturated (double) bonds in fatty acids Increase number of fatty acids with unsaturated bonds as temperature drops, less packed with phospholipids=less dense, but maintained fluidity kinkedo Increase cholesterol content of membranecholesterol is a fluid buffer Cholesterol is bulky, hydrophobic (mostly unipolar)acts like the kinky, unsaturated lipid (makes it more fluid at low temperatures- Motion of lipids will speed up at high temperature (lipids move way too fast) but cholesterol will calm the lipds down to prevent too much disorganization- With cholesterol, higher fluidity at low temps, lower fluidity at high temps- Fluidity of membrane allows uncharged, time organisms to go intothe cell- Permeability of Phospholipid Bilayero Small, uncharged molecule will move freely (O2, CO2, NO, H2O-usually)o Small hydrophobic=fat-soluble molecules (ei. Vitamins)- Transport proteins: handle traffic across membrane, cells make lots of these, makes two types 1) from in to out 2) from out to ino Two classes of transport proteins: Channels: elongated donut holes- Ei.potassium channel (only lets potassium ions)- Ei. ion channels (potassium channels is a type of ion channel- MOLECULAR SPECIFICITY: has to be a fit Carrier Proteins: “Transporters”- MOLECULAR SPECIFICITY- Ei. Glucose transporter, ribose transporter, etc.- Separate transporter for each moleculeo Energy considerations of transport Passive transport: driven by diffusion; molecules move down their concentration gradient, no energy cost to cell- Simple diffusion: small molecules (O2) move across membrane based on physical properties (small, uncharged)o Cells don’t spend energy- Facilitated Diffusion: molecules move via transport proteins (either channels or carrier proteins) larger, charged moleculeso needs protein to be built Active transport: requires energy input, genuinely deprived either directly or indirectly from ATP hydrolysis; molecules move against (“up) concentration gradiento Diffusion: tendency of molecules to spread out in space (high concentration to low concentration)- Energy from active transport comes fromo Strategy involving coupling mechanisms: link energetically unfavorable reactions with favorable reactions to drive a processo Coupling Mechanism: Link unfavorable transport reaction to ATP hydrolysis (energy-releasing rxn)- Involves pumps= ATPases- Active transport driven by ATP hydrolysisATP pumps Co-transport
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