Leyland 11 Storage of fats – triacylglycerols

Question 1

Storage of fats – triacylglycerols

Answer 1

• hydrophobic
• => stored in anhydrous form
• specialised tissue – adipose tissue
• used in prolonged exercise, in between meals /starvation and during pregnancy
• Storage / mobilisation under hormonal control

Question 2

Synthesis of fatty acids:

Answer 2

• In cytoplasm of liver & adipose tissue
• growing FA cycles through sequence of reactions
• C2 + each cycle
• consumes NADPH & ATP
• all intermediates linked to acyl carrier protein (ACP)

Question 3

Overall reaction for the synthesis of palmitate

Answer 3

8 CH3CO~CoA + 7 ATP + 14 NADPH + 6 H+ à

CH3(CH2)14COOH + 14 NADP+ + 8 CoA + 7 ADP + 7 Pi + 6 H2O

Question 4

1 Synthesis of fatty acids:

Carboxylation of acetyl CoA to form malonyl CoA:

Answer 4

• Acetyl CoA carboxylase
• Irreversible reaction
• Short term - allosteric activation by citrate and inhibited by products of FA synth
  
  • phosphorylation – glucagon inhibits
• dephosphorylation - insulin activates

Question 5

2 Synthesis of fatty acids:

Answer 5

a multi-functional enzyme complex

Question 6

3 Synthesis of fatty acids:

Elongation and desaturation

Answer 6

• C16 is the usual end-point of fatty acid synthase
• Longer FAs generated by + C2 units in smooth ER
• Desaturases in SER also + double bonds

Question 7

Ketone bodies: an alternative fuel for cells

Answer 7

• normal KB [plasma] < 1mM increases in starvation (2-10mM) & untreated type I diabetes (>10mM)
• used: fuel, particularly in starvation/uncontrolled diabetes
• used by all tissues containing mitochondria, including CNS.
• high levels => ketoacidosis

Question 8

Fed state
Happens:
Fuel molecules:
Blood Glu conc:
Energy source:

Answer 8

• shortly after feeding
• abundance
• high
• CHO, excess converted to glycogen (liver & skeletal muscle) & TAG stores (adipose)
• Lipid and/or synthesis of membranes, excess converted to TAG stores (adipose)
• Protein => new proteins, some catabolised to produce energy or converted into glycogen/TAG stores

Question 9

Fasted state
Happens:
Fuel molecules:
Blood Glu conc:
Energy source:

Answer 9

• several hours after a meal
• falling
• insulin levels starting to fall
• liver glycogen broken down to maintain blood glucose
• TAG stores mobilised to release FAs and glycerol
• some protein catabolised to produce energy