Lecture 12: Lipids & Lipoproteins

Question 1

Where are dietary TAGs processed and where are TAGs synthesized De Novo?

Answer 1

Dietary tags are processed in intestinal cells

De Novo = hepatocytes and adipocytes

Question 2

What lipoproteins are exogenously created?

Answer 2

Chylomicrons

Question 3

Dietary TAGs are broken down into ___________ and _________ in the intestinal lumen by pancreatic enzymes

Answer 3

MAG and FFA

Question 4

Intestinal cells resynthesize TAGs using what as the backbone?

Answer 4

MAG and adding FFA

Question 5

Chylomicrons released into the lymphatic system enter the blood via what?

Answer 5

The thoracic duct

Question 6

What is the enzyme that converts glycerol to glycerol-3-P and is only found in the liver?

Answer 6

Glycerol kinase

Question 7

What is the backbone for TAG synthesis in hepatocytes?

Answer 7

Glycerol-3-P

Question 8

In hepatocytes, TAGs are packaged with apolipoproteins and other lipids to form a lipoprotein called ________________

Answer 8

Very low density lipoproteins (VLDL)

Question 9

What is the enzyme responsible for breaking down chylomicrons in the blood to allow for the FFAs to be taken up by adipose tissue?

Answer 9

Capillary lipoprotein lipase

• Stimulated by insulin

Question 10

What is the receptor found on adipocytes that allows the cell to uptake glucose?

Answer 10

GLUT4

Question 11

What is the backbone for TAG synthesis in adipocytes?

Answer 11

G-3-P

Question 12

What is the final product of TAG synthesis in adipocytes?

Answer 12

TAGs! -> adipocytes store the TAGs, the arent making and secreting a lipoprotein like hepatocytes and intestinal cells

Question 13

What is hormone sensitive lipase (HSL) activity modulated by?

Answer 13

Phosphorylation

Question 14

What are the three major lipases responsible for breaking down TAGs?

Answer 14

Hormone sensitive lipase (HSL)
Lipoprotein lipase (LPL)
Monoacylglycerol lipase (MAG lipase)

Question 15

What are the 2 major hormones that activate hormone sensitive lipase (HSL)?

Answer 15

Glucagon (secreted in response to hunger)

Epinephrine (secreted in response to exercise)

Question 16

How does perilipin regulate lipolysis?

Answer 16

Perilipin is a family of proteins that coat lippid droplets in adipocytes and muscle cells controlling physical access to HSL

Question 17

Overexpression of perilipin 1 ____________ (activates/inhibits) lipolysis and its knock-out has converse effect

Answer 17

Inhibits

Question 18

What does the phosphorylation of perilipin do?

Answer 18

Loosens its hold on HS and allows the DAG to come into contact with HSL, promoting lipolysis

Question 19

What is found in the outer layer of lipoproteins?

Answer 19

Monolayer of phospholipids
Free cholesterol
Apolipoproteins

Question 20

What is found in the inner core of lipoproteins?

Answer 20

Packed with hydrophobic TAGs

Cholesterol esters

Question 21

What are teh 3 apoproteins found on chylomicrons and what is their role?

Answer 21

ApoB-48 = facilitates transport
ApoC-II = activates lipoprotein lipase
ApoE = facilitates uptake in the liver

Question 22

What is the largest and least dense lipoprotein?

Answer 22

Chylomicron

• High TAG content

Question 23

What lipoprotein is formed from dietary fats?

Answer 23

Chylomicrons

Question 24

Where is VLDL made?

Answer 24

Liver

Question 25

What apoproteins are found on VLDL?

Answer 25

ApoB-100 = acts on the receptor 
ApoC-II = acts on the receptor
ApoE = activator for the lipase

Question 26

What apoproteins are found on IDL?

Answer 26

ApoB-100

ApoE

Question 27

What apoproteins are found on LDL?

Answer 27

ApoB-100

Question 28

What is condsidered bad cholesterol?

Answer 28

LDL -> packed with cholesterol -> if it gets taken up by cells its not bad bc the cells can use it but if it sits in the blood its bad because it can buld up and form plaques

Question 29

What apoproteins are found on HDL?

Answer 29

ApoA-I
ApoC-II
ApoE

Question 30

What are the properties of HDL?

Answer 30

• Smallest lipoproteins
• Most dense
• High protein and phospholipid content

Question 31

What’s the difference between nascent and mature chylomicrons?

Answer 31

Nascent chylomicrons dont have ApoE or ApoC-II when released into the bloodstream from the intestinal cells. Once in the blood HDL supplies the with ApoE and ApoC-II at which time they become mature

Question 32

How do cells uptake LDL?

Answer 32

Cells have LDL receptors that take in LDL using the ApoB-100 proteins and send the LDL to the lysosome to be broken into raw materials that the cell can use

Question 33

HDL levels correlate positively with reduced risk for __________________

Answer 33

CAD -> coronary artery disease

Question 34

How does HDL recerse cholesterol transport?

Answer 34

It has the ability to reverse cholesterol transport from peripheral tissues to liver -> receives cholesterol from the peripheral tissues and internalizes it, once internalized the cholesterol becomes cholesterol ester making the HDL mature and able to distribute apoproteins to chylomicrons

Question 35

what does type I hyperlipoproteinemia result in the inability to do?

Answer 35

Hydrolyze TAGs in chylomicrons and VLDL

Question 36

What is the cause of type I hyperlipoproteinemia and what is the most serious cause?

Answer 36

Either a deficiency in LPL (most serious) or ApoC-II

Question 37

In type I hyperlipoproteinemia, when does LPL deficiency versus ApoC-II deficiency manifest?

Answer 37

LPL deficiency manifests in infancy

ApoC-II deficiency manifests post-adolescence

Question 38

What is the treatment for type I hyperlipoproteinemia?

Answer 38

Low fat diet

Question 39

What is the cause of Type II hyperlipoproteinemia?

Answer 39

Defects in uptake of LDL via LDL receptors -> impaired ability to recognize ApoB 100 on LDL

Question 40

What is the genetic inheritance pattern of type I versus type II hyperlipoproteinemia?

Answer 40

Type I = autosomal recessive -> homozygous

Type II = autosomal dominant -> heterozygous