Cholesterol

Question 1

What makes up the hydrophobic core?

Answer 1

Esterified Cholesterols, Triglycerides

Question 2

What makes up the hydrophilic coat

Answer 2

Amphipathic cholesterol phospholipids apoproteins

Question 3

What is the function of apoproteins?

Answer 3

act as recognition and binding sites allowing lipoproteins to bind to cells

Question 4

What apoproteins do HDL contain?

Answer 4

apoA-1 apoA-II

Question 5

What apoproteins do LDL contain?

Answer 5

apoB-100

Question 6

What apoproteins do VLDL contain?

Answer 6

apoB-100

Question 7

What apoproteins do chylomicrons contain?

Answer 7

apoB-48

Question 8

Where are chylomicrons formed?

Answer 8

In the Enterocytes that line the intestine

Question 9

Where are VLDL formed?

Answer 9

In the liver hepatocytes

Question 10

What is the function of chylomicrons?

Answer 10

Exogenous transport of dietary triglycerides

Question 11

What is the function of VLDL?

Answer 11

Endogenous transport of triglycerides synthesised in the liver

Question 12

Function of all apoB containing lipoproteins?

Answer 12

Transport triglycerides to muscles for ATP biogenesis and adipocytes for storage

Question 13

Life cycle of lipoproteins

Answer 13

Assembly
Intravascular metabolism
Receptor mediated clearance

Question 14

How are the triglycerides formed?

Answer 14

Monoglycerides and free fatty acids diffuse separately across the membrane and combine within the cell

Question 15

Which protein channel allows cholesterol into the cell?

Answer 15

NPCILI Channel

Question 16

How do lipoproteins exit the cell?

Answer 16

Via endocytosis when the correct apoprotein has been synthesised to the surface

Question 17

What must happen to chylomicrons and VLDL to become activated?

Answer 17

apoC-II must be transferred from a HDL to allow the lipoproteins to bind to the cell surface and transfer its cargo

Question 18

What receptors on the cell surface do lipoproteins bind to?

Answer 18

Lipoprotein Ligase

Question 19

Upon binding to lipoprotein ligase what happens to the VLDL and the chylomicrons?

Answer 19

They become remnants depleted in triglycerides which are removed but enriched in esters which stay

Question 20

What occurs when the lipoproteins have dissociated from the LPL?

Answer 20

apoC-II transfered for an apoE from a HDL which allows them to bind to the liver.

Question 21

Which receptor do VLDL and chylomicron remnants bind to on the hepatocytes?

Answer 21

Hepatic Ligase

Question 22

What happens upon binding to hepatic ligase?

Answer 22

VLDL and chylomicrons are further metabolised

All chylomicrons and 50% of VLDL are cleared by endocytosis into the cell

Question 23

What happens to the other 50% of VLDL which bind to hepatic ligase?

Answer 23

More triglycerides are removed and enriched in esters increasing density of particle
Lose apoE and gain apoB-100
Now a LDL particle

Question 24

What is LDL endocytosis into a cell reliant on?

Answer 24

Presence of Lipoprotein Ligase

Question 25

Upon release of cholesterol esters into the cell what happens?

Answer 25

Esters are hydrolysed to form three units of cholesterol

Question 26

What is the effect of increasing intracellular cholesterol levels?

Answer 26

Inhibits HMG-CoA reductase reducing synthesis of cholesterol
Down regulates LDL receptor expression
Can be stored as cholesterol ester or precursor for bile salt

Question 27

Function of HDL

Answer 27

Accept cholesterol from Macrophages in atheromatous plaques, and from VLL and LDL
Returns cholesterol to the liver where it can be broken down and excreted
Lowers serum cholesterol levels