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USMLE Biochemistry > Lipid metabolism > Flashcards

Lipid metabolism Flashcards

1
Q

What are the different types of lipids?

A
  • Fatty acids
  • Triglycerides
  • Cholesterol
  • Phospholipids
  • Steroids
  • Glycolipids
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2
Q

What males a triglyceride?

A

3 FAs and 1 Glycerol

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3
Q

Name the different types of lipoproteins

A
  • Chylomicrons
  • VLDL
  • IDL (intermediate density)
  • LDL (low density)
  • HDL
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4
Q

What are the largest lipoproteins?

A

Chylomicrons

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5
Q

What are the smallest lipoproteins?

A

HDL

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6
Q

What are the functions of apolipoproteins?

Where are they found?

A

Found in lipoproteins

  • Bind lipids
  • Act as surface receptors
  • Co-factors for enzymes
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7
Q

How are fatty acids absorbed in the GI tract?

A

Converted to fatty acids

- Packaged into chylomicrons by intestinal cells

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8
Q

What is cholesterol converted into in the enterocytes?

A

Cholesteryl esters

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9
Q

What converts cholesterol into cholesterol esters in the enterocytes?

A

Acyl-CoA cholesterol acyltransferase (ACAT)

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10
Q

What are Cholesteryl esters packaged into to enter the lymph?

A

Chylomicrons

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11
Q

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

A

Fatty acid

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12
Q

What can be found insode chylomicrons?

A
  • Triglycerides
  • Vitamins (ADEK)
  • Cholesteryl esters
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13
Q

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

A

Apolipoprotein B48

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14
Q

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

A

48%

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15
Q

Where is Lipoprotein lipase found?

A

Extracellularly

  • Adipose tissue, muscle and heart
  • Anchored to capillary walls
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16
Q

What tissue does not contain Lipoprotein lipase?

- What does it contain instead?

A

Not in Liver

- Hepatic lipase instead

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17
Q

What is the function of lipoprotein lipase?

A

Converts triglycerides into fatty acids (and glycerol)

- Shrinks chylomicrons by removing the fatty acids from triglycerides

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18
Q

What does lipoprotein lipase require for activation?

A

Apo C-II

- Found on chylomicron particles, VLDL/IDL

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19
Q

Where is Apo E found and what is its function?

A
  • Binds to liver receptors

- Required for uptake of remnants

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20
Q

What apoplipoproteins are secreted from HDL and given to chylomicrons?

A
  • Apo C-II

- Apo E

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21
Q

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?

A

Becomes a chylomicron remnant and is transported to the liver

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22
Q

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

A

Apo-E

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

23
Q

When are chylomicron remnants present?

A

After meals (clear 1-5 hrs)

24
Q

What appearance do chylomicron remnants have?

A

Milky

25
Q

What is the only organ that can synthesise cholesterol?

A

Liver

26
Q

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

A

HMG-CoA Synthase

- Occurs in liver

27
Q

What enzyme converts HMG-CoA to Mevalonate?

A

HMG-CoA Reductase

liver

28
Q

Mevalonate eventually gets converted to what in the liver?

A

Cholesterol

29
Q

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

A

It is scavenger lipoprotein

- It brings cholesterol back to the liver from the periphery

30
Q

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

A

Esterifies cholesterol in HDL; packs esters densely in core

31
Q

What is LCAT activated by in HDL?

A

A-I

32
Q

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

A 
Exchanges esters (HDL) for triglycerides (VLDL)
- Allows HDL to take some of the triglycerides from VLDL particles
33
Q

What is the purpose of VLDL?

A

Carries triglycerides, cholesterol to tissues from liver

34
Q

What is VLDL secreted by?

A

VLDL (with only B-100)

35
Q

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

A

HDL

36
Q

What enzymes act on VLDL in circulation to remove triglycerides?

A
  • LPL removes triglycerides

- CETP in HDL removes triglycerides

37
Q

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

A

IDL

38
Q

What acts on IDL to make it become LDL?

A
  • Hepatic lipase removes triglycerides

- HDL removes and acquires C-II and ApoE from IDL

39
Q

What is the function of hepatic lipase?

found in liver capillaries

A

Similar function to LPL (releases fatty acids)

- Important for IDL -> LDL conversion

40
Q

What is contained inside LDL?

A
  • Small amount of triglycerides

- High concentration of cholesterol / cholesterol esters

41
Q

Where does LDL transfer cholesterol to?

A

Cells with LDL receptors

42
Q

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

A

B100

43
Q

What are foam cells?

A

Macrophages filled with cholesterol

  • Contain LDL receptors and LDL
  • Found in atherosclerotic plaques
44
Q

What is lipoprotein a a modified form of?

A

LDL

45
Q

What large glycoprotein is contained in lipoprotein a?

A

Apo A

46
Q

High levels of lipoprotein a indicate what?

A

Risk of CV disease

  • Not routinely measured
  • No proven therapy
47
Q

What is abetalipoproteinemia a defect of?

A

MTP

- Microsomal triglyceride transfer protein

48
Q

How is abetalipoproteinemia inherited?

A

AR

49
Q

What proteins/structures are affected in abetalipoproteinemia?

A

Lipoproteins w. apoB

  • Chylomicrons from intestine (B48)
  • VLDL from liver (B100)
50
Q

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

A

Chylomicrons (B48)

  • Lipids accumulate in intestine
  • ADEK not absorbed

VLDL from liver (B100):
- Lack of VLDL, IDL, LDL in plamsa

51
Q

What are the clinical features of abetalipoproteinemia

A

Infancy

  • Steatorrhea
  • Abdo distension
  • Failure to thrive

Vitamin deficiencies

  • Vit E (ataxia, weakness, hemolysis)
  • Vit A - Poor vision
52
Q

What will be seen on biopsy in abetalipoproteinemia?

A

Lipid accumulation in enterocytes (cannot leave via chylomicrons)

53
Q

What are the lab findings in abetalipoproteinemia?

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

USMLE Biochemistry (44 decks)

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