biochem unit 4

Question 1

• Lipids include many types of molecules. Rather than being defined by their structure (like proteins, carbohydrates, and nucleic acids), they are defined by a property: they are largely water-insoluble but relatively soluble in hydrophobic (organic) solvents. They are either totally hydrophobic, or amphipathic (having both hydrophobic and hydrophilic parts).

Question 2

• Lipids as storage molecules

Question 3

• Many lipids contain Fatty Acids. The Fatty Acid can be the sole component of the lipid, or it may be linked to another entity by an ester or amide bond.

Question 4

• Melting Point trends of lipids

Answer 4

the longer the carbon chain, the higher the m.p.
double bonds introduce ‘kinks’ in chains, disrupt the association of adjacent chains, and so decrease the m.p. (because groups of molecules are less likely to associate to form solids); and the more double bonds (up to a point), the lower the m.p.

Question 5

• Consequence of m.p. trends of lipids

Answer 5

Saturated F.A.’s (no double bonds) are generally solids at room- or body-temperature

Unsaturated F.A.’s (with double bonds) are generally liquids at these temperatures

Question 6

Triacylglycerols = triglycerides = fats = glycerol + 3 F.A.’s (simple and mixed)
+ low density
+ stored in adipocytes

Question 7

• Advantages to storing energy in lipids:

Answer 7

Carbon atoms are highly reduced: high energy-density

No water of hydration for these hydrophobic molecules – lighter cells

Insulation

Question 8

• Fats in foods are generally mixtures of different triacylglycerols with various F.A.’s

Answer 8

vegetable oils (higher percentage of unsaturated F.A.’s: liquid)

animal fats (higher percentage of saturated F.A.’s: solid)

Question 9

• Waxes: F.A. + Alcohol (both long-chain – means m.p.’s fairly high, e.g. 60-100°C): solids, water-repellant, prevent dehydration, protect against parasites; lotions, ointments

Question 10

• Structural lipids

Question 11

• Glycerophospholipids (glycerol backbone, with phosphate; 2 F.A.’s + 1 polar group), Sphingolipids (sphingosine backbone, with or without phosphate; 1 F.A. + 1 polar group) [sphingolipids define the human blood groups: A, B, O]

Question 12

• Membrane lipids are continually degraded and replaced by enzymes in lysosomes

Question 13

• Certain genetic diseases are caused by defects in these enzymes, leading to lipid build-up (Niemann-Pick, Tay Sachs, Gaucher’s, Fabry’s, Sandhoff’s, etc.)

Question 14

• Sterols: 4 fused rings (Recognize this structure.), found in membranes of eukaryotes but not of prokaryotes (bacteria); synthesized from isoprene/isoprenoids