Session 7 ILOs - Regulation of metabolism

Question 1

Describe the various classes of lipids

Answer 1

1. Fatty Acid derivatives
   Fatty acids = fuel molecules
   Triacylglycerols (triglycerides) = fuel storage & insulation
   Phospholipids = components of membranes and plasma lipoproteins
   Eicosanoids = local mediators (signalling molecules between cells within tissues)
2. Hydroxy-methyl-glutaric acid derivatives
   Ketone bodies = water soluble fuel molecules
   Cholesterol = membranes and steroid hormone synthesis
   Cholesterol esters = form of cholesterol storage
   Bile acids & salts = lipid digestion
3. Vitamins
   A, D, E, K

Question 2

Describe how dietary triacylglycerols are processed to produce energy

Answer 2

Triacylglycerol converted to fatty acids & glycerol by pancreatic lipases by process of lipolysis (in the gut)
Fatty acids & glycerol are recombined in the small intestine and transported as Triacylglycerol by lipoproteins (chylomicrons)
Lipoproteins carry these to the consumer tissues, where fatty acids are released and undergo fatty acid oxidation

Question 3

Explain how ketone bodies are formed

Answer 3

Ketone bodies are formed in the liver
Acetyl-CoA is converted to Hydroxylmethyl glutaryl-CoA (HMG-CoA) by HMG-CoA synthase
Hydroxylmethyl glutaryl-CoA (HMG-CoA) is converted to acetoacetate by HMG-CoA lyase
Acetoacetate can then be converted to either acetone or Beta-hydroxybutyrate

Question 4

Explain when ketone bodies are formed

Answer 4

In low glucose states, fatty acids are mobilised and converted to Acetyl-CoA however this produces a lot of NADH which inhibits the enzymes in the Krebs Cycle (due to low NAD+) so Acetyl-CoA is diverted to make ketone bodies instead

Question 5

Explain why ketone bodies are formed

Answer 5

Ketone bodies are formed because they can still produce energy (when glucose is low indicating starvation)
It spares glucose for use in the brain, if ketone bodies are being used for energy production in the muscles

Question 6

Describe the central role of acetyl-CoA in metabolism

Answer 6

Acetyl-CoA is the main convergence point for catabolic pathways and can feed directly into the TCA cycle (produced from both carbohydrates and fatty acids)
Acetyl-CoA is the most important intermediate in both catabolic & anabolic pathways

Question 7

Outline fatty acid oxidation

Answer 7

Occurs in the mitochondria
Fatty acids are activated by linking to Coenzyme A outside the mitochondrion and are transported across the inter mitochrondrial membrane using a carnitine shuffle.
Fatty acid cycles through a sequence of oxidative reactions with 2 x carbons removed each cycle
Acetyl CoA can go into the Krebs Cycle (actually produces more energy from FA oxidation than glucose oxidation)

Question 8

Outline the 3 ketone bodies produced in the body

Answer 8

1. Acetoacetate
2. Acetate
3. Beta-hydroxybutyrate