Fat and lipid metabolism

22 important questions on Fat and lipid metabolism

What is the function of bile salts?

Bile salts emulsify fats into micells making them accessible to digestive enzymes.

What is important to know about fat uptake?

Fats bypass the liver after uptake

How are free FA transported from adipose tissue?

As FFA-albumin complex
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What is the difference between beta oxidation and FA synthesis?

Beta oxidation is the breakdown of FA in mitochondria, FA synthesis is the production of FA in the cytoplasm.

How are FA moved into the mitochondria?

FA are activated into fatty acyl CoA. Coenzyme A cannot pass the mitochondrial membrane and therefore it is replaced by carnitine for import into the mitochrondria.

What are the end products of palmitate (C16) in beta oxidation?

8x acetyl CoA, 7x FAD (2H), 7x NADH

Very long FA (>20 C atoms) are shortened in peroxisomes. What is the side-effect of this?

ROS production

What are the end products if the FA is odd-chain-length?

Acetyl CoA (C2) + propionyl CoA (C3)

Acetyl CoA cannot leave mitochondria. How is this done?

Acetyl CoA is converted to citrate, it moves outside and outside it is converted back to acetyl CoA.

When is the greatest flux through FA synthesis and breakdown?

Synthesis: after carbohydrate-rich meal
Breakdown: in starvation

What hormonal state is favoured in FA synthesis and breakdown?

Synthesis: high insulin/glucagon ratio
Breakdown: low insulin/glucagon ratio

What is the major tissue site of FA synthesis and breakdown?

Synthesis: liver
Breakdown: liver and muscle

What are the carriers of acyl-acetyl groups between mitochondria and cytosol in FA synthesis and breakdown?

Synthesis: citrate (mitochondria to cytosol)
Breakdown: carnitine (cytosol to mitochondria)

What are the phosphopanthetheine-containing active carriers of FA synthesis and breakdown?

Synthesis: acyl carrier protein domain, coenzyme A
Breakdown: coenzyme A

What are the oxidation/reduction cofactors of FA synthesis and breakdown?

Synthesis: NADPH
Breakdown: NAD+, FAD

What are the two-carbon donors/products of FA synthesis and breakdown?

Synthesis: malonyl CoA
Breakdown: acetyl-CoA

What are the inhibitors of FA synthesis and breakdown?

Synthesis: long-chain fatty acyl-CoA (inhibits acetyl CoA carboxylase)
Breakdown: malonyl-CoA (inhibits carnitine palmitoyltransferase)

What is boosted if [ATP] is high?

Citrate production

What is inhibited and activated when [acetyl CoA] is high?

Pyruvate dehydrogenase complex is inhibited, pyruvate carboxylase is activated.

At what two levels is the activity of malonyl production controlled?

  • AMP and citrate: energy status
  • Hormonal control: demand of the body, insulin activates phosphatase

What do you know about the (in)activation of acetyl CoA carboxylase?

Acetyl CoA carboxylase is only active as polymer. This is allosterically regulated by citrate and palmitate. Citrate partially activates acetyl CoA carboxylase. Palmitate inhibits acetyl CoA carboxylase.
Acetyl CoA is active when it is not phosphorylated. It is inactive when it is phosphorylated (glucagon phosphorylates).

What is the shuttle concept?

Citrate transport is coupled to NADH --> NADPH conversion

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