Lipoproteins

Question 1

Structure of lipoproteins

Answer 1

spherical particles with a core of hydrophobic lipids and a surface of hydrophilic apoproteins, cholesterol and phospholipids

Question 2

What is a nascent chylomicron?

Answer 2

A TG ball packaged from intestinal absorpition devoid of any apo-proteins

Question 3

Difference between nascent chylomicron and blood chylomicron

Answer 3

Nascent chylomicron is found in the lymphatic structures

Blood chylomicons are found in the blood and contain APO B48 (Major), Apo E, Apo CII

Question 4

Which apo-proteins and where do blood chylomicrons get them?

Answer 4

Apo B48: from intestines

Apo A1, Apo CII, Apo E: from HDL

Question 5

What happens to blood chylomicron and what is created?

Answer 5

Undergoes lipolysis via Lipoprotein Lipase to create free fatty acids and remnant chylomicron

Question 6

Which apo-protein is the major activator of lipoprotein lipase?

Answer 6

Apo CII

Question 7

Effect of elevated insulin on fatty acid storage?

Answer 7

elevated insulin promotes storage of FFA into adipose tissue by activating LPL in adipose tissue and inactivating LPL in muscles.

Question 8

What happens to remnant chylomicrons?

Answer 8

They are endocytosed via liver by Apo E mechanism

Question 9

Endogenous Pathway of Lipid Metabolism is during which periods?

Answer 9

Fasting (interdigestive period) (low insulin)

Question 10

Which form of cholesterol is produced (and where) during endogenous lipoprotein metabolism?

Answer 10

VLDL is produced in the liver with Apo B100

nb: VLDL is produced due to low insulin levels

Question 11

Function of VLDL

Answer 11

delivers FFA to Muscles (low insulin) by breakdown via LPL

nb: VLDL becomes IDL

Question 12

Function of IDL

Answer 12

50% IDL gets internalized by liver via Apo E mechanism

50% IDL gets degraded via LPL and Hepatic Lipase to deliver FFA to extrahepatic cells (LDL gets internalizedby LDL-R)

Question 13

Which receptor senses intracellular cholesterol levels?

Answer 13

LXR

Question 14

Which enzyme forms cholesterol esters?

Answer 14

LCAT

Question 15

Acquisition of cholesterol esters causes shift from what molecule to what new molecule?

Answer 15

Nascent HDL to HDL3

Then HDL3 to HDL2

Question 16

Function of HDL2

Answer 16

transfer cholesterol to VLDL, LDL, IDL in exchange for TG

Question 17

What protein acts on HDL2 to release cholesterol esters

Answer 17

SRB1

Question 18

Cholesterol is synthesized by what precursor molecule?

Answer 18

Acetyl-CoA

Question 19

What is the rate limiting step in cholesterol synthesis and what is the enzyme

Answer 19

HMG-CoA to Mevalonate via HMG-CoA Reductase

Question 20

Basic Mechanism of statins?

Answer 20

Statins inhibit HMG-CoA Reductase to lower cholesterol synthesis
Increase expression of LDL-R for internalization of LDL

Question 21

What amino acid is epinephrine derived from?

Answer 21

Tyrosine