Zoology 101: Animal BiologyLast Lecture Outline Lecture 4 1. Proteins • 4 structure levels • Enzymes2. Lipids• Sterols Current Outline 1. Cholesterol• LDL• HDL2. Fats and Oils (Triglycerides)3. Phospholipids• Membrane remodeling4. What do membrane proteins do?Cholesterol• Largely hydrophobic; moves through lipoprotein complex → sequesters cholesterol from aqueous environment of blood (Cholesterol is in the middle with hydrophobic ends of phospholipid surrounding, hydrophilic end of phospholipid point out towards bloodstream (allowing cholesterol to move)• LDL (Low Density Lipoprotein): carries cholesterol from liver (where it is synthesized) to body cells. “Bad” Cholesterol• HDL (High Density Lipoprotein): picks up excess cholesterol from cells → delivers to liver for disposal/recycle. “Good” Cholesterol Fats, Oils, and Triglycerides• Energy Storage (ex. Avocado, nuts, meats, olive oil)• 3 fatty acids (Long H-C chains) on a glycerol backbone • dehydration reaction--> one fatty acid will pop off, can under go dehydration again• Saturated fats: no double bonds, tightly packed, solid at room temp ◦ Increase LDL• Unsaturated fats: double bonds are present, carbons are not saturated, bending and kinking due to double bonds, loosely packed and liquid at room temperature◦ Decrease LDL and increase HDL• Shape dictates behavior Phospholipids• main component of cell membrane• only 2 fatty acids attached to a glycerol backbone ◦ Amphipathic: both hydrophobic and hydrophilic◦ Heads: hydrophilic; tails: hydrophobic• In water, micelles form (basically a lipoprotein), micelles group form together and form bilayers (basis of cell membranes)• biological membranes are selectively permeable (decided what goes in and out)◦ main component: phospholipid bilayer◦ steroid (cholesterol snuggled in phospholipids) help stay strong to maintain the structure ◦ move laterally in the bilayer ◦ proteins move slower than phospholipids• Fluidity◦ temp: increased body temp → membrane denatures/melts ◦ decreased body temp → membrane becomes less fluid/permeable (solidifies) • Fatty acid composition of phospholipids ◦ saturated → less permeable ◦ unsaturated → greater movement (kinked)• Cholesterol: can fill gaps left by unsaturated fatty acids ◦ decreases fluidity◦ increases strength Membrane Remodeling • Regulation in lipid composition in response to change in environment• occurs in bacteria plants and poikiloterms• desaturases → saturated fats and inserts double bond; membrane more fluid What do cell membrane proteins do? • Cell membrane proteins are: enzymes, cell-cell receptors, responsible for attachment, cell joining, signaling and transport. • Passive transport (moves across membrane via diffusion)◦ simple diffusion ◦ facilitated diffusion◦ osmosis• Active Transport• Vesicular (bulk)
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