Lipids & Membranes Quiz

Lipids Overview

• Lipids are hydrophobic compounds which are soluble in organic solvents.
• Most lipids are amphipathic, featuring both a non-polar and a polar end.

Fatty Acids

• Fatty acids consist of a hydrocarbon chain with a carboxylic acid group at one end.
• Example structure of a 16-carbon fatty acid: CH3(CH2)14-COO-.
• Double bonds in fatty acids typically have a cis configuration, causing a "kink" in the chain.
• Common fatty acids include:
  • 14:0 myristic acid
  • 16:0 palmitic acid
  • 18:0 stearic acid
  • 18:1 cisD9 oleic acid
  • 18:2 cisD9,12 linoleic acid
  • 18:3 cisD9,12,15 α-linolenic acid
  • 20:4 cisD5,8,11,14 arachidonic acid
  • 20:5 cisD5,8,11,14,17 eicosapentaenoic acid (an omega-3)

Glycerophospholipids

• Glycerophospholipids (phosphoglycerides) are major components of cellular membranes.
• Comprised of a glycerol backbone and two esterified fatty acids on carbon positions 1 and 2, with carbon 3 esterified to phosphate (Pi).

Ester Formation

• Esters form through the reaction of a hydroxyl group with a carboxylic acid, releasing water (H2O).
• General ester formation reaction: R'OH + HO-C-R" → R'-O-C-R'' + H2O.

Structure of Phosphatidate

• In phosphatidate, two fatty acids are attached to a glycerol backbone, and a phosphate group is attached to the third carbon (C3).

Glycerophospholipid Diversity

• Glycerophospholipids often have diverse polar head groups, such as serine, choline, ethanolamine, glycerol, or inositol.
• Variations in fatty acids may occur in length or presence of double bonds, resulting in non-identical tails.

Example Glycerophospholipids

• Phosphatidylinositol serves as both a membrane lipid and plays a role in cell signaling.
• Phosphatidylcholine, with its choline head group, is another common membrane lipid.

Molecular Structure

• Each glycerophospholipid consists of a polar region (glycerol, carbonyl oxygen from fatty acids, phosphate, and polar head group) and non-polar hydrocarbon tails (fatty acids R1, R2).
• The presence of double bonds in fatty acids introduces kinks, affecting membrane fluidity.