Lipoproteins I

Question 1

…………… are spherical macromolecular complexes of lipids and specific proteins

Answer 1

Lipoproteins

Question 2

…………. are lipoproteins formed in the blood from VLDL (via IDL) and deliver cholesteryl esters to cells that need cholesterol (mainly for cell membranes).

Answer 2

LDL (Beta-Lipoprotein)

Question 3

……small lipoproteins involved with the reverse cholesterol transport to the liver and are filled in the blood with cholesteryl esters.

Answer 3

HDL (alpha-Lipoprotein)

Question 4

…………..are lipoproteins released by the liver and contain TAGs and cholesteryl esters that were formed by the liver (endogenous source).

Answer 4

VLDL (pre-Beta Lipoprotein)

Question 5

………….. are the lipoproteins released by the intestinal mucosal cells which contain dietary lipids (exogenous source) and lipid-soluble vitamins.

Answer 5

Chylomicrons

Question 6

…….. float on top of the blood sample when separated by ultra-centrifugation

Answer 6

Chylomicrons, then the next layers are:

2. Very low density lipoproteins (VLDL)
3. Intermediate density lipoproteins (IDL) 4. Low density lipoproteins (LDL)
4. High density lipoproteins (HDL)

Question 7

The purpose of chylomicrons is to………

Answer 7

Transport dietary lipids away from intestinal mucosal cells by the lymph system and later into the blood circulation.

Question 8

……… cleaves most of the Triacylglycerols (TAGs) of Chylomicron

Answer 8

Lipoprotein Lipases (LPL)

Question 9

Lipoproteins are anchored in the capillaries of the ………, ………, and ………..

Answer 9

Heart, Muscle, Adipose Tissue

Question 10

The chylomicron remnants have the function to deliver the dietary cholesteryl esters and other particles to the ……….

Answer 10

Liver

Question 11

Chylomicrons need ……… and ……… to be released into the lymph.

Answer 11

Apo B-48

MTP- Microsomal TAG transfer protein

Question 12

Chylomicrons are nascent (functionally incomplete) until they collide with ……. and transfer ……….. and ………

Answer 12

HDL

Apo- E and Apo-CII

Question 13

……….. Activates Lipoprotein Lipase

Answer 13

Apo C-II

Question 14

……….. Allows entry of chylomicrons remnants into the liver.

Answer 14

Apo E

Question 15

Free fatty acids produced by the cleavage action of Liproprotein Lipase are taken up by ………. or …………

Answer 15

Muscle or Fat cells

Question 16

Cardiac lipoprotein lipase activity is ………….

Answer 16

Insulin-Independent

The heart always takes up fatty acids for its energy metabolism

Question 17

Adipocyte LPL activity is

Answer 17

Insulin-dependent

When chylomicrons and VLDL are abundant then the generated fatty acids are taken up into fat cells and stored as TAGs.

Question 18

…………. enhances in adipocytes the synthesis of LPL and its placement in the capillaries.

Answer 18

Insulin

Question 19

Inside of fat cells, insulin activates the synthesis of …… for storage after uptake of free fatty acid from the blood

Answer 19

TAGs

Question 20

The chylomicron remnant contains apo E and apo B-48 as …… is returned to HDL

Answer 20

Apo-C

Question 21

Remnant receptors on the liver recognizes apo E allow the endocytosis of ……..

Answer 21

Chylomicron remnants

Question 22

……….. released by hepatocytes contains only Apo B-100 until HDL adds during collision Apo C and Apo E

Answer 22

Nascent VLDL

Question 23

Purposes of VLDL:

Answer 23

1. to prevent TAG accumulation in hepatocytes and
2. to provide substrates for lipoprotein lipase resulting in fatty acids for other cells.
3. to generate eventually LDL which can distribute cholesteryl esters to the cells that require it

Question 24

Cleavage of TAGs from VLDL creates the VLDL remnant, …….

Answer 24

IDL

Question 25

IDL is either taken up into the liver via the remnant receptor or …………….

Answer 25

Acts as a substrate for hepatic lipase (hepatic TAG lipase HTGL) which will form LDL in the blood of hepatic capillaries.

Question 26

Which lipoprotein is absent in blood of fasting healthy individuals?

Answer 26

Chylomicrons

Question 27

Which lipoprotein has the highest % of cholesterol?

Answer 27

LDL

Question 28

…….. formed by hepatic lipase in the capillaries of the liver from IDL in the blood

Answer 28

LDL

Question 29

Purpose of LDL

Answer 29

To transport cholesteryl esters in the blood and deliver cholesterol to cells that need it for their plasma membranes or for steroid hormone synthesis

Question 30

The LDL receptor in the coated pit on the liver membrane recognizes ………in LDL and the uptake is performed via endocytosis.

Answer 30

Apo B-100

Question 31

The pH of the endosome allows the separation of LDL from the receptor and the LDL receptor can be…………

Answer 31

Recycled

Question 32

At high free cholesterol levels the cytosolic enzyme …….. is activated and a reservoir of cholesteryl esters is formed.

Answer 32

(fatty) Acyl CoA cholesterol acyl transferase (ACAT)

Question 33

If there is still high free cholesterol left in cytosol after the activation of ACAT then ….. is synthesized and also of LDL receptors are down-regulated

Answer 33

HMG CoA reductase (regulated enzyme of cholesterol synthesis)

Question 34

In the liver after a cholesterol-rich meal the uptake of chylomicron remnants lead to high free cytosol cholesterol levels which ……….. LDL-receptor synthesis.


Answer 34

Reduces.

This leads to temporary increased levels of serum LDL.

Question 35

Deficient recognition of ……. on chylomicron remnants leads to accumulation of IDL and chylomicron remnants in the blood.

Answer 35

Apo-E

Question 36

Inactivation of Lipoprotein Lipase due to a deficiency in …… leads to elevated levels of chylomicrons and of VLDL in the blood

Answer 36

Apo C-II