L35:Biological membranes

• What is one function of the cell membrane?


  It acts as a semipermeable barrier.
• What is a characteristic of eukaryotic cells mentioned in the study material?

  Eukaryotic cells are compartmentalized.
• What model describes the structure of membranes?

  The fluid mosaic model.
• Who proposed the lipid composition of membranes in 1972?

  Jonathan Singer and Garth Nicolson
• What is the lipid composition of myelin by weight?

  Myelin is composed of 18% protein and 79% lipid.
• What are the key biological functions of lipids?

  • Fuel for metabolism (e.g., triacylglycerides)
  • Components of membranes (e.g., phospholipids, glycolipids, cholesterol)
  • Signaling molecules (e.g., steroid hormones)
  • Vitamins (e.g., A, D, E, K)
• Why are lipids defined by their hydrophobicity?

  Because they are not soluble in water.
• What property do phospholipids have?

  Phospholipids are amphipathic.
• What are the three key characteristics of lipid bilayers?

  1. Extensive
  2. Close in on themselves – no edges
  3. Self-sealing
• What forms the "tails" of phospholipids and triacylglycerides?

  Fatty acids form the "tails".
• What defines saturated fatty acids?

  Saturated fatty acids have no C=C double bonds.
• What is the typical structure of unsaturated fatty acids?

  Unsaturated fatty acids have C=C double bonds.
• How does the presence of C=C double bonds affect fatty acids?

  It introduces a kink in the chain, causing irregular packing.
• What are essential fatty acids that must be obtained from the diet?

  Linoleic acid and linolenic acid
• What is arachidonic acid synthesized from?

  Arachidonic acid is synthesized from linoleic acid.
• What role do eicosanoids play in the body?

  Eicosanoids are important in pain and inflammation signaling.
• What are the components of phospholipids?

  • Glycerol
  • Fatty acids (two)
  • Phosphate group
• What is the function of phosphatidylinositol in cell signaling?

  Phosphatidylinositol can be cleaved to transmit signals into the cell.
• What are sphingolipids based on?

  Sphingolipids are based on the amino alcohol sphingosine.
• What type of bond is found in sphingomyelin?

  Sphingomyelin contains an amide bond, not an ester bond.
• What is the role of the myelin sheath?

  The myelin sheath increases the speed of electrical impulses in nerve axons.
• What are the functions of glycolipids?

  • Immune responses
  • Cell-cell recognition
  • Attachment
• What is the primary role of cholesterol in membranes?

  Cholesterol affects membrane fluidity.
• What are the three main types of lipids in membranes?

  • Phospholipids (phosphoglycerides and sphingolipids)
  • Glycolipids
  • Cholesterol
• What are some features of the fluid mosaic model?

  Semi-fluid, not static. Lipid bilayer.
• What is the function of a particular membrane largely defined by?

  The protein molecules and complexes which reside in it.
• What is cholesterol important for?

  Regulating the fluidity of the membrane
• Why is it important to match carbohydrates between donors and patients?

  You get an immune reaction.
• What are the membrane lipids soluble in?

  Organic solvents such as chloroform.
• Key points on Glycerol derivatives:

  • Storage of fuel for metabolism
  • Phosphoglycerates are a key component of biological membranes
• There are 3 systems for numbering the carbons in saturated fatty acids:

  • 1,2,3...
  • Alpha, beta, gamma... (Used in metabolism)
  • Omega, omega-1, omega-2... (Used in nutrition)
• What is the rule for melting points with saturated fatty acids?

  The longer the chain, the higher the melting point
• • Most fatty acids have an even number of carbons,but odd numbered ones do exist
• Are double bonds in unsaturated fatty acids usually cis or trans?


  Cis (this introduces a kink in the chain, whilst trans are almost straight)
• Kinky chains cannot pack tightly and are therefore more liquid, trans chains are more straight so can form solids (butter)
• What is arachidonic acid used for?

  Functions as part of phospholipids in membrane; plays important role in inflammation
• Why is the top of the phospholipid more negatively charged?

  BC it has a phosphate grps which is even.
• What are two key types of phospholipid?

  Phosphoglycerates; Sphingolipids
• What does demyelination lead to?

  Disease, e.g. multiple sclerosis
• Describe the basic structure of a glycolipids.

  They are a sugar containing lipid (there is a sugar instead of a phosphate grp). There can be more than one sugar unit.