Met 1: Complex Lipids Flashcards
Compare the polarity of membrane lipids and storage lipids
Membrane lipids are AMPHIPATHIC
Storage lipids are ENTIRELY NONPOLAR
What are the 3 components of a glycerophospholipid?
- Glycerol backbone
- Two fatty acids
- Phosphate with R group
What type of lipid is phosphatidylcholine?
Phosphatidylcholine is a glycerol-based phospholipid
What is phosphatidic acid?
Glycerol backbone + 2 FA’s + phosphate
What are 3 ways to add an R group to a phosphatidic acid?
- Activating glycerol backbone or R group via CDP addition
- Exchange R group
- De novo synthesis
What is the backbone for sphingolipids?
Sphingosine (derived from amino acids)
What is special about phosphoinositol?
It’s used in signaling
eg. PI-3 (phosphoinositol 3)
What is ceramide?
sphingosine + 2 Fatty acids
(basic structure of sphingolipids)
*imagine a ceramic sphinx
Where is sphingomyelin used in the body?
Nervous sytem
What is the precursor for arachidonic acid?
What are 3 derivatives of arachidonic acid?
- Precursor: Linoleic acid (essential fat)
- Derivatives: Leukotrienes, PG’s, TXA2
What are glycolipids?
Sphingolipids where the R group is a carbohydrate
Which is more polar: free cholesterol or cholesterol ester?
Free cholesterol is more polar because it still has a hydroxyl group
What are two uses of cholesterol?
Steroid hormones
Membranes
What are 2 ways for the liver to get new cholesterol?
What are 2 ways for the liver to recover cholesterol?
New cholesterol: from diet, de novo synthesis
Recover cholesterol: bile reabsorption in ileum, LDL receptor takes up cholesterol from blood
What are 3 potential fates for liver cholesterol?
- Secretion of free cholesterol in bile
- Conversion into bile acids
- Secretion as VLDL
How is cholesterol made from acetylcoA?
- Acetyl-coA converted to HMG-coA
- by HMG coA Synthase
- HMG coA converted to Mevalonate
- by HMG coA reductase
- this requires NADPH
- Mevalonate converted to cholesterol
- this requires ATP, NADPH
Where in the cell does cholesterol synthesis occur?
cytoplasm
What are two places that HMG-coA synthase can be found?
- HMG-coA synthase is used in MITOCHONDRIAL MATRIX during ketone synthesis
- HMG-coA synthase is used in HEPATOCYTE CYTOSOL during cholesterol synthesis
What is the rate limiting step in cholesterol synthesis?
Name 3 ways it’s regulated
Rate limiting: HMG coA Reductase action (conversion of HMG coA into mevalonate)
Regulation:
- insulin (dephosphorylation) activates it
- enzymatic degradation is controlled
- transcriptional regulation
Compare the action of HMG coA synthase and HMG coA reductase
- 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
Describe transcriptional regulation of HMG-coA reductase activity
- 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
