Lipid metabolism

Question 1

What are the different types of lipids?

Answer 1

• Fatty acids
• Triglycerides
• Cholesterol
• Phospholipids
• Steroids
• Glycolipids

Question 2

What males a triglyceride?

Answer 2

3 FAs and 1 Glycerol

Question 3

Name the different types of lipoproteins

Answer 3

• Chylomicrons
• VLDL
• IDL (intermediate density)
• LDL (low density)
• HDL

Question 4

What are the largest lipoproteins?

Answer 4

Chylomicrons

Question 5

What are the smallest lipoproteins?

Answer 5

HDL

Question 6

What are the functions of apolipoproteins?

Where are they found?

Answer 6

Found in lipoproteins

• Bind lipids
• Act as surface receptors
• Co-factors for enzymes

Question 7

How are fatty acids absorbed in the GI tract?

Answer 7

Converted to fatty acids

- Packaged into chylomicrons by intestinal cells

Question 8

What is cholesterol converted into in the enterocytes?

Answer 8

Cholesteryl esters

Question 9

What converts cholesterol into cholesterol esters in the enterocytes?

Answer 9

Acyl-CoA cholesterol acyltransferase (ACAT)

Question 10

What are Cholesteryl esters packaged into to enter the lymph?

Answer 10

Chylomicrons

Question 11

What does ACAT add to the cholesterol to create a cholesteryl ester?

Answer 11

Fatty acid

Question 12

What can be found insode chylomicrons?

Answer 12

• Triglycerides
• Vitamins (ADEK)
• Cholesteryl esters

Question 13

What apolipoprotein found on chylomicrons is required for secretion from their enterocytes?

Answer 13

Apolipoprotein B48

Question 14

How much apo-B protein is contained on apolipoprotein B48?

Answer 14

48%

Question 15

Where is Lipoprotein lipase found?

Answer 15

Extracellularly

• Adipose tissue, muscle and heart
• Anchored to capillary walls

Question 16

What tissue does not contain Lipoprotein lipase?

- What does it contain instead?

Answer 16

Not in Liver

- Hepatic lipase instead

Question 17

What is the function of lipoprotein lipase?

Answer 17

Converts triglycerides into fatty acids (and glycerol)

- Shrinks chylomicrons by removing the fatty acids from triglycerides

Question 18

What does lipoprotein lipase require for activation?

Answer 18

Apo C-II

- Found on chylomicron particles, VLDL/IDL

Question 19

Where is Apo E found and what is its function?

Answer 19

• Binds to liver receptors

- Required for uptake of remnants

Question 20

What apoplipoproteins are secreted from HDL and given to chylomicrons?

Answer 20

• Apo C-II

- Apo E

Question 21

What does the chylomicron become and what organ does it go to after Lipoprotein lipase has offloaded its fatty acids to muscle and adipose tissue?

Answer 21

Becomes a chylomicron remnant and is transported to the liver

Question 22

Chylomicron remnants are able to be taken up by the liver through expression of what receptors?

Answer 22

Apo-E

- ApoE receptors are able to take up remnants via receptor-mediated endocytosis

Question 23

When are chylomicron remnants present?

Answer 23

After meals (clear 1-5 hrs)

Question 24

What appearance do chylomicron remnants have?

Answer 24

Milky

Question 25

What is the only organ that can synthesise cholesterol?

Answer 25

Liver

Question 26

What enzyme combines Acetyl-CoA and Acetoacetyl-COA to make HMG-CoA?

Answer 26

HMG-CoA Synthase | - Occurs in liver

Question 27

What enzyme converts HMG-CoA to Mevalonate?

Answer 27

HMG-CoA Reductase | liver

Question 28

Mevalonate eventually gets converted to what in the liver?

Answer 28

Cholesterol

Question 29

Why can high levels of HDL be associated with lower levels of cardiovascular disease?

Answer 29

It is scavenger lipoprotein | - It brings cholesterol back to the liver from the periphery

Question 30

HDL contains the enzyme LCAT (Lecithin-cholesterol acyl transferase) what does this do?

Answer 30

Esterifies cholesterol in HDL; packs esters densely in core

Question 31

What is LCAT activated by in HDL?

Answer 31

A-I

Question 32

What is the function of CETP (Cholesteryl ester tranasfer protein)?

Answer 32

``` Exchanges esters (HDL) for triglycerides (VLDL) - Allows HDL to take some of the triglycerides from VLDL particles ```

Question 33

What is the purpose of VLDL?

Answer 33

Carries triglycerides, cholesterol to tissues from liver

Question 34

What is VLDL secreted by?

Answer 34

VLDL (with only B-100)

Question 35

VLDL pciks up Apo E and C-II from what?

Answer 35

HDL

Question 36

What enzymes act on VLDL in circulation to remove triglycerides?

Answer 36

- LPL removes triglycerides | - CETP in HDL removes triglycerides

Question 37

What does VLDL become after the removal of many triglycerides by LPL and CETP?

Answer 37

IDL

Question 38

What acts on IDL to make it become LDL?

Answer 38

- Hepatic lipase removes triglycerides | - HDL removes and acquires C-II and ApoE from IDL

Question 39

What is the function of hepatic lipase? | found in liver capillaries

Answer 39

Similar function to LPL (releases fatty acids) | - Important for IDL -> LDL conversion

Question 40

What is contained inside LDL?

Answer 40

- Small amount of triglycerides | - High concentration of cholesterol / cholesterol esters

Question 41

Where does LDL transfer cholesterol to?

Answer 41

Cells with LDL receptors

Question 42

What do the cells with LDL receptors recognise on the LDL?

Answer 42

B100

Question 43

What are foam cells?

Answer 43

Macrophages filled with cholesterol - Contain LDL receptors and LDL - Found in atherosclerotic plaques

Question 44

What is lipoprotein a a modified form of?

Answer 44

LDL

Question 45

What large glycoprotein is contained in lipoprotein a?

Answer 45

Apo A

Question 46

High levels of lipoprotein a indicate what?

Answer 46

Risk of CV disease - Not routinely measured - No proven therapy

Question 47

What is abetalipoproteinemia a defect of?

Answer 47

MTP | - Microsomal triglyceride transfer protein

Question 48

How is abetalipoproteinemia inherited?

Answer 48

AR

Question 49

What proteins/structures are affected in abetalipoproteinemia?

Answer 49

Lipoproteins w. apoB - Chylomicrons from intestine (B48) - VLDL from liver (B100)

Question 50

What are the effects of abetalipoproteinemia in respect to lacking chylomicrons (B48) and VLDL (B100)?

Answer 50

Chylomicrons (B48) - Lipids accumulate in intestine - ADEK not absorbed VLDL from liver (B100): - Lack of VLDL, IDL, LDL in plamsa

Question 51

What are the clinical features of abetalipoproteinemia

Answer 51

Infancy - Steatorrhea - Abdo distension - Failure to thrive Vitamin deficiencies - Vit E (ataxia, weakness, hemolysis) - Vit A - Poor vision

Question 52

What will be seen on biopsy in abetalipoproteinemia?

Answer 52

Lipid accumulation in enterocytes (cannot leave via chylomicrons)

Question 53

What are the lab findings in abetalipoproteinemia?

Answer 53

- Low or zero VLDL/IDL/LDL - Very low triglyceride and total cholesterol levels - Low vit E - Acanthocytosis (abnormal RBC membrane lipids)