Fate of lipids

Question 1

What is beta-oxidation?

Answer 1

catabolic process in which fatty acids are broken down to generate acetyl CoA which can enter the krebs cycle

Question 2

Where do chylomicrons go?

Answer 2

synthesis in intestinal epithelial cells => lymph => blood => mature chylomicrons => adipose cells
Lipoprotein lipase (LPL) digests TAGs of chylomicrons to fatty acids and glycerol
Fatty acids are oxidised in muscle or stored in adipose cells as TAGs
remnants of chylomicron taken up and digested by the liver

Question 3

What is lipogenesis?

Answer 3

metabolic formation of fatty acids from excess dietary carbs (glucose converted to Acetyl CoA => fat synthesis) or protein in the liver
Fatty acids combined with a glycerol molecule => TAGs

Question 4

How are TAGs exported from the hepatocytes?

Answer 4

packaged with cholesterol, phopholipids and proteins => VLDL
VLDLs secreted into blood

Question 5

What happens to fatty acids in the circulation in the fed state?

Answer 5

Lipoprotein lipase cleaves TAGs in both VLDL and chylomicrons => fatty acids and glycerol
Fatty acids enter adipose cells and are activated => fatty acetyl CoA => reacts with glycerol-3-phosphate (formed from glucose) => TAGs => stored as large fat droplets in adipose tissue
glycerol travels to liver to become TAGs

Question 6

DEscribe lipid metabolism in the fasting/starved state

Answer 6

During fasting - adipose TAGs are mobilised (lipolysis) => fatty acids and glycerol released into blood
Fatty acids transported in blood with albumin are oxidised for energy in cells
Glycerol used to produce energy via gluconeogenesis in liver
Increased amount of fat mobilised at starvation as decreased AAs used

Question 7

How are ketone bodies produced?

Answer 7

beta-oxidation of fatty acids produces Acetyl CoA during prolonged fasting
Acetyl CoA converted to ketone bodies in liver
ketone bodies oxidised to produce energy

Question 8

Describe the stages of fatty acid oxidation

Answer 8

Beta-oxidation:
- fatty acid => acetyl CoA + NADH + FADH
Oxidation of acetyl CoA:
- into Co2 in Krebs cycle
- produces NADH + FADH2 through oxidative phosphorylation
ATP generation:
- ATP generated from NADH and FADH via respiratory electron chain