Isoprenoids..

• What is structure of a sterol?

  Steroid nucleus with four fused rings , hydroxyl group in A ring , various nonpolar side chains , steroid nucleus is almost planar

  
• What is the physiological role of sterols?

  stabilize plasma membrane , thicken the membrane , obtained via food or synthesizing it
• What are the characteristics of steroid hormones?

  Steroids are oxidized derivatives of sterols , sterols nucleus but lack alkyl chain , more polar than cholesterol , hormones are synthesized from cholesterol in gonad
• What are the characteristics of vitamin D?

  regulated calcium uptake
• What are the characteristics of eicosanoids?

  enzymatic oxidation of arachidonic acid yields prostaglands , thromboxanes , leukotrienes
• What are the characteristics of isoprenoids?

  sweet smelling , vitamin A is involved in visual pigment , precursor for other hormones invovled in signaling , vitamin e and K and other lipid quinones are antioxidants , pigments

  
• What is a micelle?


  Forms in solution of amphipathic molecules that have larger head than tail , aggregation occurs when concentration of molecules is higher than a certain threshold
• What are the characteristics of the membrane bilayer?

  Consists of two leaflets of lipids monolayers , head groups interact with water , tails are packed inside
• What are the characteristics of liposomes?

  small bilayers will spontaneously seal into spherical vesicles , central aqueous cavity can enclose dissolved molecules , useful artificial carriers of molecules
• What are the characteristics of biological membranes?

  Complex lipid based structures that form pliable sheets , composed of a variety of lipids and proteins , some membrane lipids and proteins are glycosylated , all cells have a cell membrane which separates the cell from its surrounding
• What are the functions of membranes?

  define boundaries of cell , allow import and export of molecules , retain metabolites , sense external signals , provide compartmentalization , store energy as a proton gradient
• What are some common features of membranes?

  sheet like flexible structure , form spontaneously in solution , stabilized by noncovalent forces , asymmetric , fluid
• What is the fluid mosaic model?

  Lipids form a viscous 2D solvent into which proteins are inserted and integrated more or less deeply , integral proteins are firmly associated with membrane
• What is the composition of membranes?

  It is different in each tissue , organ and organism, cholesterol predominant in plasma membrane , galactolipids abundant in plant chloroplasts
• What are lipid rafts?


  Lipid rafts are collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules; these rafts often serve in signaling.
• What are the functions of membrane proteins?

  Receptors : detecting signals from outside

  Channels , gates , pumps

  enzyme
• What are the characteristics of integral membrane proteins?

  Span the entire membrane , have asymmetry , tightly associated with membrane
• What are the characteristics of peripheral membrane proteins?

  Loosely associated with the membrane through ionic interactions with lipids , lipid linked , GPI anchored
• What are the characteristics of asymmetry in membranes?

  Lipids: Outer and inner leaflets have different lipid compositions

  
  

  proteins: Peripheral membrane proteins are only associated with one side , integral membrane proteins have different domains on different sides of membrane , specific lipid modification of proteins targets the protein to a specific leaflet

  
  

  Carbohydrates: only on the outside of cells
• What are the physical properties of membranes?

  Dynamic and flexible structures , can exist in various phases , not permeable to large polar solutes and ions , permeable to small polar solutes
• How is membrane fluidity controlled?

  Membrane fluidity is determined by fatty acid composition , more fluid membranes require shorter and more unsaturated fatty acids
• What are membrane dynamics?

  Individual lipids undergo fast lateral diffusion within the leaflet , spontaneous flips from one leaflet to another are rare (charged head has to transverse the hydrophobic tail region) , special enzymes (flippases) catalyze transverse diffusion ; they use energy of atp to move lipids against the concentration gradient