Fatty acid metabolism

Question 1

What are the physiological roles of fatty acids?

Answer 1

1 - building blocks of phospholipids and glycolipids

2 - attach to proteins to target them to membrane locations

3 - fuel molecules, stored as triaglycerols

4 - fatty acid derivatives serve as hormones and intracellular messengers

Question 2

Role of adipose cells?

Answer 2

major site of accumulation of triacylglycerols are the adipose cells

these cells are specialised for synthesis and storage of triacylglycerols

Question 3

What are the 5 phases of lipid digestion/absorption?

Answer 3

• large oil phase - TAG droplets are emulsified partly by the stomach first to smaller emulsion droplets
• mixed micelles are formed by bile acids and other lipase enzymes
• Hydrolysis of TAG to FFA and monoacylglycerol within the lumen
• Uptake of FFA and MAG via specific FAT and FATP1 transport proteins
• TAG packaged into chylomicrons which enter the lacteal and lymphatic circulation. medium chain fatty acids directly enter capillary

Question 4

Describe fatty acid de novo synthesis

Answer 4

• predominantly in the liver
• substrate for synthesis is acetyle-coA

synthesis requires

• cytosolic acetyle-coA
• NAPH
• catalysed by fatty acid synthase
• first step is the synthesis of Malonyl-CoA from Acetyle-CoA

Question 5

What are the three steps in which fatty acids are synthesised?

Answer 5

1 - a malonyl unit is condensed with an acyl group

2 - carbonyl is then reduced, dehydrated and reduced, increasing the acyl chain length by two

3 - another activated malonyl group condenses with the growing acyl group unit and the process repeats until C16 FA is synthesised

Question 6

What is the difference between fatty acid synthesis and fatty acid degradation?

Answer 6

synthesis:
- elongates the acyl chain
- occurs in the cytosol
- intermediates are covalently linked to sulphurhydryl groups of an acyl carrier protein
- utilises a large enzyme complex (fatty acid synthase)
- the reductant is NADPH

degradation:
- shortens the acyl chain
- occurs in the mitochondrial matrix
- intermediates are covalently linked to the sulphurhydryl group of coenzyme A
- no such associations seem to exist for the degradative enzymes
- the oxidants in degradation are NAD+ and FAD

Question 7

What is fatty acid degradation?

Answer 7

converts an aliphatic compound into a set of activated acetyl units

Question 8

How are fatty acids degraded?

Answer 8

1 - oxidation to introduce a double bond

2 - double bond is hydrated

3 - the new alcohol group is oxidised to a ketone

4 - thiolysis results in cleavage by CoA