CPR 17 - Lipoproteins 1

Question 1

Answer 1

Question 2

What lipids cannot be transported through blood by albumin? How are they transported?

Answer 2

Question 3

What are lipoproteins and what do they do?

Answer 3

Question 4

Describe the basic structure of a lipoprotein and how that structure enables it transport lipids through the blood.

Answer 4

Question 5

Answer 5

Question 6

What are the functions of apolipoproteins?

Answer 6

Question 7

What are chylomicrons? Where do they come from and what do they contain?

Answer 7

Question 8

What are VLDLs? Where do they come from and what do they contain?

Answer 8

Question 9

What are LDLs? Where do they come from and what do they carry?

Answer 9

Question 10

What are HDLs? What do they do and what do they contain?

Answer 10

Question 11

How are lipoproteins separated by ultra centrifugation?

Answer 11

Question 12

How are lipoproteins separated by electrophoresis?

Answer 12

Question 13

List the molecules found in a chylomicron and state what percentage each accounts for.

Answer 13

TAGs - 90%

Cholesterol/Cholesterol Esters - 5%

Lipid Soluble Vitamins (A, D, E, and K) - 5%

Question 14

Answer 14

Question 15

Where is apo B48 found and how is it synthesized?

Answer 15

Question 16

What cells synthesize chylomicrons? How do they do this?

Answer 16

Question 17

What type of chylomicron is released by intestinal mucosal cells? Why are they called this?

Answer 17

Nascent chylomicrons

Because they’re functionally incomplete

Question 18

How does a nascent chylomicron become a mature chylomicron?

Answer 18

Question 19

What cleaves TAGs off of lipoproteins? Where is this enzyme found? Is it constitutively active?

Answer 19

Question 20

What happens to the free fatty acids cleaved off of lipoproteins?

Answer 20

They are taken up into muscle or fat cells

Question 21

How is LPL activity regulated? How does this vary by tissue type?

Answer 21

Question 22

Where is the most LDL found and why?

Answer 22

Question 23

How does insulin affect LPLs in adipocytes?

Answer 23

Question 24

What is a chylomicron remnant and what happens to it?

Answer 24

Question 25

What forms a VLDL? What do they contain primarily? Give percentages.

Answer 25

Formed in hepatocytes and contain endogenous lipids TAGs - 60% Cholesterol/Cholesterol Esters - 20%

Question 26

How does a nascent VLDL become a functional VLDL?

Answer 26

Question 27

What are the primary funcions of VLDLs?

Answer 27

1. To prevent TAG accumulation in hepatocytes 2. To provide substrates for LPL resulting in fatty acids for other cells 3. To generate LDL which can distribute cholesterol esters to cells that need it

Question 28

What is the VLDL remnant? How does it become this? What is its function?

Answer 28

Question 29

Answer 29

Question 30

When will chylomicrons not be seen in the blood?

Answer 30

When a person has been fasting

Question 31

Which lipoprotein has the highest percentage cholesterol? Give its percentage of cholesterols and TAGs.

Answer 31

LDL Cholesterol/Cholesterol Esters - 50% TAGs - 8%

Question 32

Where are LDLs formed and how? What are the primary functions?

Answer 32

They are formed by hepatic lipase in the capillaries of the liver from IDL in the blood. Their purpose is to transport cholesterol esters in the blood and deliver cholesterol to cells that need it for their plasma membranes or steroid hormone synthesis.

Question 33

Where is most LDL found and why?

Answer 33

Question 34

Answer 34

Question 35

Describe how LDL and IDL are endocytosed by hepatocytes.

Answer 35

Question 36

How and when do hepatocytes store cholesterol?

Answer 36

Question 37

What is HMG CoA reductase? How does it respond to high cytosolic cholesterol levels?

Answer 37

HMG CoA reductase is an enzyme that is crucial to the pathway that forms cholesterols from acetyl CoA. When cytosolic cholesterol levels are high this enzyme is inhibited.

Question 38

How does LDL receptor expression respond to cholesterol levels? Why is this important?

Answer 38

Question 39

Answer 39

Question 40

Describe what occurs in the liver, in relation to cholesterol, after a cholesterol rich meal.

Answer 40

Question 41

What is the function of Apo B48 and where does it come from?

Answer 41

Apo B48 is needed for synthesis and release of chylomicrons and VLDL. They are structural components of these lipoproteins and are not interchanged with HDL. Therefore, they only come from the hepatocytes that synthesize the lipoprotein.

Question 42

What is the function of Apo B100 and where does it come from?

Answer 42

Apo B100 is needed for synthesis and release of chylomicrons and VLDL. It is also needed for recognition by the LDL receptor. They are structural components of these lipoproteins and are not interchanged with HDL. Therefore, they only come from the hepatocytes that synthesize the lipoprotein.

Question 43

What leads to the formation of foamy cells?

Answer 43

The oxidation of Apo B100 to oxLDL and its subsequent uptake by macrophages

Question 44

What is the primary function of Apo E? What occurs if it is deficient?

Answer 44

Question 45

What is the primary function of Apo C-II? What happens if it is deficient?

Answer 45

Question 46

Answer 46

Question 47

Can oxLDLs be taken up by hepatocytes via the LDL receptor?

Answer 47

No

Question 48

What can take up an oxLDL and how? Why is this important?

Answer 48