Anabolic Metabolism: Triglyceride Synthesis and Transport

Question 1

Explain how insulin and cytosolic [citrate] stimulate fatty acid synthesis in hepatocytes.

Answer 1

Insulin - released when blood sugar rise = promotes the absorption and storage of sugars which activates pyruvate dehydrogenase (PDH);

[citrate] - citrate is converted to OAA and Acetyl CoA (which is then converted to fatty acids), so high [citrate] levels = higher fatty acid synthesis. [citrate] reinforces Acetyl CoA Carboxylase

Question 2

Describe how CO2 is used to activate acetyl groups for fatty acids synthesis.

Answer 2

CO2 is added to Acetyl CoA to make a 3 carbon molecule, then two carbons are added to FA chain and CO2 is released

Question 3

Identify the sources of NADPH + H+ that is used to reduce the acetyl group during fatty acid synthesis

Answer 3

NADPH comes from the pentose phosphate pathway

produced when G-6-P is converted to Glycerol

Question 4

Explain how the majority of fatty acids released during lipogenesis are cycled between adipose and liver

Answer 4

Chylomicrons carry dietary cholesterol esthers and triacylglycerides from small intestine to extra hepatic tissues cleaving off TAGs. Remnants cycle back to liver and CE are packaged with synthesized TAGs as VLDL. VLDL ciirculates blood, dropping off TAGs, Remnant is just CE called IDL and returns to liver. In liver, IDL is turned to LDL which returns to circulation to drop liver synthesized CD to tissues. LDL remain in circulation to drop off CE. Liver synthesizes and releases HDL to pick up excess CE from extra hepatic cells

Question 5

Follow a fatty acid from synthesis to leaving hepatocytes as a triacylglyceride within a VLDL lipoprotein

Answer 5

VLDL - circulation dropping off TAG to cells - becomes IDL and returns to liver - turned into LDL - returns to circulation to drop off Cholesterol - HDL is synthesized to retrieve excess CE.

Question 6

Compare the 4 major types of lipoproteins, their components, tissue of synthesis and tissue of degradation.

Answer 6

Apo C2 - Activates lipoprotein lipase(cuts FA off carrier so it can leave into tissue)

Apo B48 - binds to LDL receptor in the liver

Apo E - bind LDL receptor

Apo B100 - bind LDL receptors

Apo A1 - activates LCAT

Question 7

Interrelate the triacylglycerol cycle gluconeogenesis & Glyceroneogenesis

Answer 7

Acetyl CoA