Human metabolism lecture 7

Question 1

Chlyomicron

Answer 1

• Used to transport TAGS from diet to adipose (storage) or skeletal/cardiac for oxidation

Question 2

VLDL

Answer 2

• Carry fat made from liver

- As transport TAG from liver to muscle/adipose, metabolised to IDL

Question 3

LDL

Answer 3

• Transport cholesterol into body

Question 4

HDL

Answer 4

• Carries cholesterol out of body

Question 5

Lipoprotein structure

Answer 5

• Surface = phospholipid monolayer
• Core = TAG, cholesterol esters
• Chylomicron = largest + least dense, 99:1 lipid: protein, apolipoprotein B48, A1,2,C,E
• VLDL 92:1, HDL 50:50

Question 6

Types of apolipoprotein

Answer 6

• Non-exchangeble e.g. ApoB48 + ApoB100 (e.g. of mRNA editing)
• All others = exchangeable

Question 7

LCAT

Answer 7

• Activated by A1

- Converts free cholesterol to esterified cholesterol

Question 8

TAG transport

Answer 8

• In starved state, body TAG mobilised as FA

- In fed, dietary TAG is transported to adipose for storage or skeletal/cardiac for oxidation

Question 9

Dietary fat → body fat

Exogenous pathway

Answer 9

• Cholesterol is made by liver + enters circulation as a lipoprotein or is secreted into bile
• TAGs x cross cell membrane intact, need to be hydrolysed + re-synthesised
• Gastric lipases break TAG → DAG + MAG
• Pancreatic lipases → monoacylglycerol + 2FA
• Bile salts avoid product accumulation at interface
• Bile salts removed w/ collapse
• Glycerol phosphate pathway

Question 10

Re-synthesis of TAG

Answer 10

• Newly made chylomicrons get exchangeable apoC11 + E from HDL in circulation
• ER, PCTVs, Golgi
• MTP
• Smooth ER + RER, core expansion

Question 11

Lipoprotein lipase

Answer 11

• Chylomicron arrives at adipose, needs to be hydrolysed
• Completely hydrolyse TAG → FFA
• Glycerol 3 phosphate pathway
• Adipose x express glycerol kinase, get it from glycolysis via gly 3 P dehydrogenase

Question 12

Insulin + body fat

Answer 12

• Insulin stimulates GLUT4 so glycolysis
• This ↑ supply of glyc 3 p so FA esterification
• Inhibits lipolysis by PKB phosph phosphodiesterase 3B, ↓ cAMP
• Insulin stimulates transcription of lipoprotein lipase + FA synthesis E by activating SRBEP1c

Question 13

Endogenous pathway

Answer 13

• Cholesterol made by liver + enters circulation
• Dominant pathway for TAG synthesis in liver = glyc 3 phosph pathway + liver has glycerol kinase
• VLDL released into circulation → acquires ApoCII + E → lipoprotein lipase makes IDL → LDL by ApoB100 addition → IDL taken up by liver