Chapter 28 and 29 - Lipid Biosynthesis Flashcards
fatty acid synthase (FAS)
a multi enzyme complex that synthesize fatty acids
FA chain length is increased by sequential addition of …
2-carbon units
elongation of FA stops with the formation of..
palmitate
site of fatty acid biosynthesis
cytosol
transport of acetyl CoA out of mitochondria in the form of..
citrate
ATP-citrate lyase
cleaves citrate at the cost of a molecule of ATP to yield cytoplasmic acetyl CoA and oxaloacetate
malonyl CoA
activated form of acetyl CoA
acetyl CoA carboxylase
catalyzes the first and rate limiting step of FA biosynthesis
- carboxylation of acetyl CoA to malonyl CoA
- irreversible
acetyl CoA carboxylase has a ______ prosthetic group
biotin
fatty acid synthase
a complex of distinct enzymes that data;yzes the synthesis of saturated long chain FA from acetyl CoA, malonyl CoA, and NADPH
fatty acid synthase in bacteria, plants
seven activities in seven separate polypeptides
fatty acid synthase in yeast
seven activities in two separate polypeptides
fatty acid synthase in vertebrates
seven activities in one large polypeptide
acetyl transacylase
catalyze the formation of acetyl ACP from Acetyl CoA
malonyl transacylase
catalyze the formation of malonyl ACP from malonyl-CoA
Intermediates of FA synthesis remain attached to FAS via…?
2 thiol groups
REVIEW
FAS steps
FAS stops at ….
palmitate, 16C
most fatty acids are long that…
palimatate.. 18-26C
fatty acid elongation
- occurs in ER
- 2 carbons added at a time from malonyl CoA
how does fatty acid elongation work?
reactions use malonyl CoA to add two-carbon units sequentially to the carboxyl ends of both saturated and unsaturated acyl CoA substrates
fatty acid desaturation
introduction of CIS double bonds
-catalyzed by desaturase enzymes (specific for location of double bond)
Humans lack ___ and ___ desaturases.
delta12 and delta15; therefore, linoleate and a-linoleate are considered essential fatty acids
Cholesterol is a lipid synthesized by virtually all cells, but especially…
liver
functions of cholesterol
- structural component of membranes
- precursor of bile salts, steroid hormones, and vit D.
cholesterol structure
- 27 carbons
- all C-atoms come from acetyl CoA
- synthesized in cytosol and ER
- 4 fused rings, a hydrocarbon tail, -OH group on C3 and double bond at C5 and C6
cholesterol biosynthetic pathways
acetyl CoA to cholesterol
- 25 rxns
- 4 stages
step 1 of cholesterol biosynthetic pathway
- synthesis of mevalonate
- catalyzed by 3-hydroxy-3-methylglutaryl CoA reductase
- irreversible
Cholesterol is stored as….
cholesterol ester
cholesterol is transported by…
lipoproteins
- TA: chylomicrons and VLDL
- cholesterols: LDL and HDL
How is cholesterol synthesis regulated?
- balance between synthesis and dietary uptake
- feedback inhibition by cholesterol
famililal hypercholesterolemia
- High cholesterol levels promote atherosclerosis
- characterized by high concentrations of cholesterol and LDL in the plasma
- cholesterol is deposited in various tissues because of the high concentration of LDL cholesterol in the plasma (defective LDL receptors)
famililal hypercholesterolemia treatment
statins (cholesterol lowering drugs): competitive inhibitors of HMG CoA reductase
acyltransferase
catalyze sequential attachment of fatty acids to glycerol backbone (ester bond)
synthesis of phsophatidylcholine
liver possesses an enzyme, phosphatidylethanolamine methyltransferase, that synthesizes phosphatidylcholine from phosphatidylethanolamine when dietary choline is insufficient.
eicosanoid
- specialized fatty acids
- signaling molecules, hormone-like actions
- 20C polyunsaturated fatty acid (arachidonate)
biological actions of eicosanoid
vasodilation, constriction, platelet aggregation, inhibition of platelet aggregation, contraction of smooth muscle, chemotaxis of leukocytes, release of lysosomal enzymes
excess eicosanoid production symptoms
pain, inflammation, fever, nausea, vomiting
phospholipase A2
release arachidonate
eicosanoids are derived from..
arachidonate
arachidonate
a 20:4 fatty acid derived from linoleate
-major precursor of several classes of signal molecules (prostaglandins, leukotrienes: called eicosanoids)
