S6- Lipid metabolism

Question 1

What are the 3 classes of lipids?

Answer 1

1. ) Fatty acid derivatives:
   - Fatty acids (fuel molecules)
   - Triacylglycerols (TAGS)- fuel storage and insulation
2. ) Hydroxy-methyl-glutaric acid derivatives:
   - Ketone bodies: water soluble fuel molecules
3. Vitamins: A,D,E and K (from diet)

Question 2

Outline the structure of Triacylglycerols (TAGS) and relate it to its function

Answer 2

• consist of a glycerol molecule and 3 fatty acid chains
• hydrophobic, stored in anhydrous form (blobs of fat)
• stored in adipose tissue as excess energy
• utilised in prolonged exercise, starvation and in pregnancy

Question 3

Where does TAG breakdown occur?

Answer 3

in the GI tract, extracellular

during stage 1

Question 4

Outline how TAGS are stored in the body?

Answer 4

1. in the GI tract broken into FA and glycerol by lipiases
2. FA are repackacged into lipoprotein structures called chylomicrons
3. chylomicrons released into circulation travel to adipose tissues where they are stored as TAG
4. They are then transported in blood as a FA-albumin complex (FA alone are hydrophobic)
5. until they reach tissues e.g. muscles where they will be oxidised for energy when needed

Question 5

What cells cannot metabolise TAGS and why?

Answer 5

• cells without a mitochondria e.g. RBC

- Brain: FA do not pass blood brain barrier

Question 6

What are the steps of FA metabolism?

Answer 6

1. Fatty acid activation by linking to coenzyme A to form fatty acyl-coA in cytoplasm
2. Fatty acyl-CoA transported across inner mitochondrial membrane using carnitine shuttle (too big to cross itself)
3. FA cycles through a sequence of beta oxidative reaction with 2c removed each cycle

Question 7

Where is glycerol metabolised?

Answer 7

Liver

Question 8

Why is Acetyl-CoA so important in metabolism?

Answer 8

• it is the main convergence point for catabolic pathways
• a big precursor for biosynthesis: produces FA (which produce TAGS and phospholipids), carbon dioxide and hydroxymethylgluatric acid (produces ketone bodies and cholesterol)

Question 9

What are the 3 ketone bodies produced in the body?

Answer 9

• Acetoacetate
• acetone
• B-hydroxybutyrate

Question 10

What are the plasma ketone body concentrations in the following situations:

a) Normal
b) Starvation (physiological ketosis)
c) Untreated type 1 diabetes

Answer 10

a) Less than 1 mM
b) 2-10 mM
c) more than 10 mM

Question 11

Where are ketone bodies synthesised?

Answer 11

Liver mitochondria