TOPIC 9 LIPID METABOLISM OBJs

Question 1

1. Identify the basic structure of a triglyceride

Answer 1

1 glycerol backboone with 3 fatty acids attached

Question 2

Lipids are

Answer 2

water insoluble

Question 3

2. Describe the digestion of lipids in humans and explain the role of bile salts

Answer 3

• Lipid digestion only occurs in the small intestine
• Pancreatic juice
  a. Has inactivate pancreatic lipase
  b. Colipase activates pancreatic lipase
  c. Hydrolyses and digests fat
  d. Emulsification makes lipids more accessible to digestive enzymes by increasing the surface area for them to act
• Bile salts
  a. Bile breaks fats down to fatty acids
  b. Glycololic acid and taurocholic acid
  c. Bile salts are important for stabilizing emulsified fats

Question 4

Majority of lipid digestion occurs in

Answer 4

small intestine

Question 5

what is responsible for emulsification and where

Answer 5

bile in the small intestine

Question 6

emulsification

Answer 6

breaking water insuble ‘glob’ into smaller pieces - increases the surface area of hydrophobic lipid droplets

Question 7

Triglycerides by lipase are cleaved into

Answer 7

glycerol (monosac) and free fatty acids

Question 8

4. Explain why triglycerides are an important store of energy for the body

Answer 8

• Triglycerides are a concentrated store of energy
• This is because they are largely:
  o Anhydrous (no water)
  o Saturated (no C=C double bonds)
• Can store a lot more energy (per gram of weight) than more hydrous forms e.g. carbohydrates

Question 9

5. Describe how triglycerides are mobilized from adipose tissue

Answer 9

• Most triglycerides are stored as adipose tissue
• Before the stored energy can be released, the triglycerides must be mobilised
• This mobilisation occurs via an enzyme called adipose tissue lipase
• Lipase is under strict hormonal control
  o Activated by glucagon, adrenaline
  o Inhibited by insulin

Question 10

7. Explain how and why a fatty acid is activated prior to β-oxidation

Answer 10

• Activated by reacting with CoA and energy to form fatty acyl CoA – done to ensure the fatty acid doesn’t leave the cell

Question 11

9. Identify the two unique enzymes required for β-oxidation of unsaturated fatty acids and relate their role to the location of double-bonds in a fatty acid

Answer 11

• The CH=CH-CH=CH group is referred to as a conjugated double bond system
• A conjugated double bond system has delocalized electrons
• This means that enoyl hydrase (step 3) cannot recognise this enoyl CoA
• There is a two-step process to overcome this problem:
  1. Reductase
  2. Isomerase
• Reductase reduces 2 double bonds to 1
• Isomerase moves the position of the double bond
• If the double bond is on an even-numbered carbon, both reductase and isomerase are required
  If the double bond is on an odd-numbered carbon, only isomerase is required

Question 12

10. Distinguish between the end products of β-oxidation of even- and uneven-numbered fatty acids

Answer 12

• Uneven produces propionyl CoA as well as acetyl CoA

Question 13

12. Compare and contrast the operation of glyoxylate and TCA cycles

Answer 13