Transport of fats

Question 1

What are the general components of a lipoprotein?

Answer 1

The shell is made of apoproteins, phospholipids, and unesterified cholesterol

Question 2

What is the general change in composition of lipoproteins as they increase in density?

Answer 2

They tend to become smaller; and have increased levels of cholesterol and protein relative to triacylglycerides

Question 3

Where are the ApoB-48 proteins found and what is the difference between it and the ApoB-100?

Answer 3

They exist mainly on chylomicrons; their RNA transcripts are edited to introduce a stop codon that eliminates the LDL receptor binding region

Question 4

Which lipoproteins have ApoB-100 on their surfaces?

Answer 4

VLDL, IDL, and LDL

Question 5

What is the role of lipoprotein lipase? Where is it found?

Answer 5

It exists on capillary endothelium of muscle cells, adipose tissue and active mammary gland cells; when activated by Apo-CII, it will release fatty acids from TAGs and absorb them

Question 6

What is the role of ACAT?

Answer 6

It esterifies cholesterol that comes into cells from the lipoproteins

Question 7

What is the role of LCAT?

Answer 7

It is found on HDLs and converts cholesterol remnants in chylomicrons and VLDL to cholesterol esters for transport. Needs ApoA-1

Question 8

What is the role of CETP?

Answer 8

It will transfer TAG and cholesterols between lipoproteins

Question 9

What is the transport role of chylomicrons?

Answer 9

They ferry TAGs to adipocytes

Question 10

What is the transport role of VLDL and LDL?

Answer 10

They ferry TAGs and cholesterol respectively from the liver to the peripheral tissues

Question 11

What is the transport role of HDLs?

Answer 11

They will ferry excess cholesterol from the periphery to the liver

Question 12

What are the main apoproteins on chylomicrons?

Answer 12

ApoB-48, ApoE, ApoC-II

Question 13

What apoproteins are commonly found on VLDL, IDL, and LDL?

Answer 13

ApoB-100, ApoC-II (VLDL and IDL have Apo-E)

Question 14

How do VLDLs become converted to other types of carriers?

Answer 14

As they lose their fatty acids, they gain density and become IDLs; as IDL lose their ApoE proteins they become LDLs

Question 15

How are LDLs processed by peripheral cells?

Answer 15

Instead of taking fatty acids out of the lipoprotein, the cell engulfs the whole packed through the LDL receptor and conjugates the cholesterol components with oleic acid

Question 16

How does familial hypercholesterolemia occur?

Answer 16

Genetic mutations in the LDL receptors prevent the individual from absorbing LDLs

Question 17

How do HDLs morphologically change over the course of their jobs?

Answer 17

They start out discoid when they are empty and as they fill they become spheroid

Question 18

How do HDLs lose their acquired cholesterols?

Answer 18

They bind to the SR-B1 receptor on the liver surface and cholesterol is extracted

Question 19

How the LDLreceptor gene regulated?

Answer 19

The SREBP system also controls transcription of the receptor; if cholesterol levels in the cell are high, then the receptor will be downregulated

Question 20

What percentage of bile salts are recycled daily?

Answer 20

95%; the 5% that is excreted is the body’s main way of eliminating cholesterol

Question 21

How is cholesterol converted to a bile salt?

Answer 21

A cytochrome P-450 enzyme, cholesterol-7-alpha-hydroxylase uses oxygen to introduce polarity to cholesterol.

Question 22

How are bile acids conjugated?

Answer 22

They are transformed to strong acids by addiition of glycine or taurine to the carboxylic acid region of the bile acid

Question 23

How is bile salt synthesis regulated?

Answer 23

High serum cholesterol levels promote upregulation of the 7-alpha-hydroxylase; high bile salt levels inhibit transcription

Question 24

What are desired, borderline, and high levels of serum cholesterol?

Answer 24

Desired is less than 190 mg/dL; borderline is 200-240 mg/dL; High is in excess of 240 mg/dL

Question 25

What are optimal targets for LDL and HDL levels?

Answer 25

LDL levels should be 100-129 mg/dL; HDL levels should be around 50 mg/dL

Question 26

How can ApoE be correlative with Alzheimer’s risk?

Answer 26

Patients who are homozygous for the E4 variant have a much higher risk of developing late onset Alzheimers