Met 1: Complex Lipids

Question 1

Compare the polarity of membrane lipids and storage lipids

Answer 1

Membrane lipids are AMPHIPATHIC

Storage lipids are ENTIRELY NONPOLAR

Question 2

What are the 3 components of a glycerophospholipid?

Answer 2

1. Glycerol backbone
2. Two fatty acids
3. Phosphate with R group

Question 3

What type of lipid is phosphatidylcholine?

Answer 3

Phosphatidylcholine is a glycerol-based phospholipid

Question 4

What is phosphatidic acid?

Answer 4

Glycerol backbone + 2 FA’s + phosphate

Question 5

What are 3 ways to add an R group to a phosphatidic acid?

Answer 5

1. Activating glycerol backbone or R group via CDP addition
2. Exchange R group
3. De novo synthesis

Question 6

What is the backbone for sphingolipids?

Answer 6

Sphingosine (derived from amino acids)

Question 7

What is special about phosphoinositol?

Answer 7

It’s used in signaling

eg. PI-3 (phosphoinositol 3)

Question 8

What is ceramide?

Answer 8

sphingosine + 2 Fatty acids

(basic structure of sphingolipids)

*imagine a ceramic sphinx

Question 9

Where is sphingomyelin used in the body?

Answer 9

Nervous sytem

Question 10

What is the precursor for arachidonic acid?

What are 3 derivatives of arachidonic acid?

Answer 10

• Precursor: Linoleic acid (essential fat)
• Derivatives: Leukotrienes, PG’s, TXA2

Question 11

What are glycolipids?

Answer 11

Sphingolipids where the R group is a carbohydrate

Question 12

Which is more polar: free cholesterol or cholesterol ester?

Answer 12

Free cholesterol is more polar because it still has a hydroxyl group

Question 13

What are two uses of cholesterol?

Answer 13

Steroid hormones

Membranes

Question 14

What are 2 ways for the liver to get new cholesterol?

What are 2 ways for the liver to recover cholesterol?

Answer 14

New cholesterol: from diet, de novo synthesis

Recover cholesterol: bile reabsorption in ileum, LDL receptor takes up cholesterol from blood

Question 15

What are 3 potential fates for liver cholesterol?

Answer 15

1. Secretion of free cholesterol in bile
2. Conversion into bile acids
3. Secretion as VLDL

Question 16

How is cholesterol made from acetylcoA?

Answer 16

1. Acetyl-coA converted to HMG-coA
   
   • by HMG coA Synthase
2. HMG coA converted to Mevalonate
   
   • by HMG coA reductase
   • this requires NADPH
3. Mevalonate converted to cholesterol
   
   • this requires ATP, NADPH

Question 17

Where in the cell does cholesterol synthesis occur?

Answer 17

cytoplasm

Question 18

What are two places that HMG-coA synthase can be found?

Answer 18

1. HMG-coA synthase is used in MITOCHONDRIAL MATRIX during ketone synthesis
2. HMG-coA synthase is used in HEPATOCYTE CYTOSOL during cholesterol synthesis

Question 19

What is the rate limiting step in cholesterol synthesis?

Name 3 ways it’s regulated

Answer 19

Rate limiting: HMG coA Reductase action (conversion of HMG coA into mevalonate)

Regulation:

• insulin (dephosphorylation) activates it
• enzymatic degradation is controlled
• transcriptional regulation

Question 20

Compare the action of HMG coA synthase and HMG coA reductase

Answer 20

• HMG coA synthase makes HMG coA
• HMG coA reductase converts HMG coA into mevalonate
• Both function in cholesterol synthesis
• Only HMG coA synthase is also functional in ketone synthesis

Question 21

Describe transcriptional regulation of HMG-coA reductase activity

Answer 21

• SREBP can bind to enhancer and activate transcription of HMG-coA reductase
• When cholesterol levels are normal, SREBP-SCAP is bound to ER membrane
• When cholesterol levels drop, SREBP-SCAP gets cleaved and SREBP moves to nucleus to upregulate transcription