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Biochemistry: Lipids and Biological Membranes

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Terms in this set (23)

  • What are lipids and their general property?

    Lipids are organic molecules characterized by low solubility in water, making them hydrophobic.

  • Name the main biological functions of lipids.

    Energy storage, insulation, water repellency, buoyancy control, membrane structure, enzyme cofactors, signaling molecules, pigments, and antioxidants.

  • What distinguishes storage lipids from membrane lipids?

    Storage lipids mainly store energy (e.g., triacylglycerols), while membrane lipids form cell membranes and are amphipathic (e.g., glycerophospholipids).

  • Describe the structure of a fatty acid.

    A fatty acid consists of a carboxylic acid group attached to a long hydrocarbon chain (4-36 carbons), usually unbranched and with an even number of carbons.

  • Difference between saturated and unsaturated fatty acids.

    Saturated fatty acids have no double bonds; unsaturated fatty acids have one or more cis double bonds causing kinks in the chain.

  • How are fatty acids named systematically?

    By chain length:number of double bonds(Δposition of double bonds), e.g., 18:1(Δ9) for oleic acid.

  • What is a triacylglycerol (TAG)?

    A molecule with three fatty acids esterified to a glycerol backbone; primary form of lipid energy storage.

  • Why are fats more efficient energy storage than carbohydrates?

    Fats have more reduced carbons (9 kcal/g vs. 4 kcal/g) and are hydrophobic, storing less water and causing less osmotic stress.

  • What are the main classes of membrane lipids?

    Glycerophospholipids, sphingolipids, and sterols; all are amphipathic with hydrophobic tails and hydrophilic heads.

  • Describe glycerophospholipids structure.

    Backbone of L-glycerol-3-phosphate with two fatty acid tails and a polar, charged head group.

  • What is the backbone of sphingolipids?

    A long-chain amino alcohol called sphingosine, not glycerol.

  • How do glycosphingolipids relate to blood groups?

    Oligosaccharide head groups on glycosphingolipids determine blood types A, B, AB, or O based on specific glycosyltransferase enzymes.

  • What is the structure of sterols like cholesterol?

    Four fused rings (steroid nucleus) with a polar hydroxyl group and various nonpolar side chains; cholesterol modulates membrane fluidity.

  • What are steroid hormones derived from?

    Oxidized derivatives of sterols, synthesized from cholesterol, acting as signaling molecules.

  • Name important lipid-derived vitamins and their functions.

    Vitamin A (vision, growth), D (calcium regulation), E (antioxidant), and K (blood clotting cofactor).

  • How does fatty acid chain length affect melting point?

    Increasing chain length increases melting point due to stronger hydrophobic interactions.

  • How do double bonds affect fatty acid melting point?

    Double bonds (cis) introduce kinks, reducing packing and lowering melting point.

  • What is the effect of trans fatty acids on membrane properties?

    Trans fats adopt extended conformations like saturated fats, pack tightly, have higher melting points, and increase cardiovascular risk.

  • What determines membrane fluidity?

    Fatty acid composition (chain length and saturation) and cholesterol content regulate membrane fluidity and phase state.

  • Describe the three types of membrane proteins.

    Peripheral (loosely associated), amphitropic (reversibly associate), and integral (embedded with hydrophobic regions spanning membrane).

  • What is the difference between monotopic, bitopic, and polytopic integral membrane proteins?

    Monotopic penetrate one leaflet, bitopic span both leaflets once, polytopic span multiple times.

  • What are the main types of solute transport across membranes?

    Passive transport (down gradient), facilitated diffusion (carrier-mediated), and active transport (against gradient using energy).

  • What is primary vs. secondary active transport?

    Primary uses ATP hydrolysis directly; secondary couples transport of one solute down its gradient to drive another solute against its gradient.