Lipid Physiology

Question 1

Describe the enzymes involved in the breakdown and buildup of triglycerides and cholesterol esters.

Answer 1

Lipases break down triglycerides into FAs and glycerol.
Fatty acyltransferases build up FAs and glycerol into triglycerides.

Cholesterol esterase breaks down cholesterol ester into cholesterol and FAs.
Cholesterol acyltransferase builds up cholesterol and FAs into cholesterol ester.

Question 2

How are fatty acids and cholesterol absorbed in intestinal cells?

Answer 2

TRansporters are used

Fatty acids use fatty acid translocase and fatty acid transport protein (FATP)
Cholesterol uses cholesterol transporter NPC1L1

Lipases/cholesterol esterases chop up triglycerides/cholesterol esters into absorbable components. Once in cells, they reform into these larger molecules.

Question 3

What is the liver’s role in fat metabolism and distribution?

Answer 3

• Burns triglycerides
• Stores triglycerides
• Distribution of fats/cholesterol to other tissues
• COnversion of cholesterol to bile acids

Question 4

Describe the loading/unloading involve with lipoproteins and their enzymes/cofactors

Answer 4

LPs are formed inside cells, and exit via exocytosis. They can be re-uptaken through LDL receptors (apoB protein)

LPs can be unloaded/loaded while circulating

• FA unloaded by lipoprotein lipase (apoCII)
• Cholesterol loaded by ABC transporter (apoA1)
• Cholesterol unloaded by scavenger receptor class B type 1 (SR-B1)

Question 5

What do chylomicrons, LDLs and HDLs do?

Answer 5

CMs are made in gut. Loaded with dietary lipids and distribute.

LDLs produced in liver. Loaded with endogenous lipids and distribute.

HDLs produced in liver. Pick up cholesterol from body.

All send to liver.

Question 6

How are cholesterol levels regulated?

Answer 6

Cholesterol exerts negative feedback.

1. Inhibit synthesis (HMG-CoA reductase activity reduced)
2. BLock uptake (Reduced LDL receptor expression)
3. Safer storage (stimulated acylation - additiion of FA chains)