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BioChem exam 4 questions with 100% correct answers
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BioChem exam 4 questions with 100% correct answers
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BioChem exam 4 questions with 100%correct answers
Where is cholesterol primarily synthesized? - correct answer ✔✔liver, intestine, adrenal cortex, and
reproductive tissues
What is the structure of cholesterol? - correct answer ✔✔4 fused hydrocarbon rings (steroid nucleus) w/
8 Branched chain attached to C-17 of D ring, -OH at C-3 of ring A, and double bond between C-5&6 of
ring B
What is cholesteryl ester structure? - correct answer ✔✔cholesterol w/ FA connected to -OH of ring A
Where are cholesterols found and in specialized tissues what is it a precursor of? - correct answer
✔✔membranes and precursor of bile acids, steroid hormones, and vit. D
What mediates intestinal uptake of cholesterol? - correct answer ✔✔Niemann-Pick-like 1 protein (target
of ezetimibe drug- reduces dietary cholesterol uptake)
why should you "eat you greens"? - correct answer ✔✔plant sterols are poorly absorbed by humans and
are actively transported back into intestinal lumen, carrying some cholesterol with them, so they reduce
plasma cholesterol levels
In cholesterol synthesis, what provides the carbons and reducing equivalents? - correct answer
✔✔acetyl CoA and NADPH
Where are the enzymes required for cholesterol synthesis in the cell? - correct answer ✔✔cytosol, SER
membrane, and peroxisome
What are the first 2 steps of cholesterol synthesis? - correct answer ✔✔acetyl CoA + acetyl CoA --
thiolase--> acoacetyl CoA + acetyl CoA --HMG CoA synthase--> HMG CoA
(basically just combining 3 acetyl CoAs to get HMG CoA)
,What is the 3rd step of cholesterol synthesis? - correct answer ✔✔RATE LIMITING
happens in cytosol
HMG CoA reduced by HMG CoA reductase (on SER membrane) to mevalonate
What is the rate limiting step of cholesterol synthesis? - correct answer ✔✔the 3rd step:
HMG CoA reductase
reducing HMG CoA to mevalonate
Following the production of mevalonate (6C) what occurs to get us cholesterol (27C)? - correct answer
✔✔mevalonate --> IPP (5C) x3 --> FPP (15C) x2 --> squalene (30C) --> lanosterol (30C) --> cholesterol
(27C)
What are the 4 ways HMG CoA reductase is regulated? - correct answer ✔✔1) expression of reductase
gene
when cholesterol levels are low = increase in expression via transcription factor SREBP-2 bound to to a
SRE
2) accelerated degradation of reductase protein when cholesterol levels are high
3) phosphorylation - causing inactivation of reductase by AMPK and dephosphorylation - activation by
phosphoprotein phosphatase
4) hormonal regulation by insulin and glucagon
insulin -> favors dephosphorylation (activation of reductase)
glucagon -> favors phosphorylation (inactivation of reductase)
What are competitive inhibitors of HMG CoA reductase and what are they used for? - correct answer
✔✔statins and are used to decrease plasma cholesterol levels (hypercholesterolemia)
How is cholesterol eliminated from your body? - correct answer ✔✔conversion to bile salts (steroid
nucleus) or by secretion into bile
what are the most important components of bile? - correct answer ✔✔PC (phosphatidylcholine or
lecithin) and bile salts
, where is bile synthesized and then sent (2 possible places)? - correct answer ✔✔synthesized in liver then
sent to duodenum or stored in gallbladder
why can bile salt/acid act as emulsifying agents? - correct answer ✔✔have non polar and polar surfaces
what is the 1st step in bile acid synthesis? - correct answer ✔✔RATE LIMITING
cholesterol -> 7-a-hydroxycholesterol by cholesterol-7-a-hydroxylase
inhibited by bile acids
what is the rate limiting step of bile acid synthesis and what is it inhibited by? - correct answer ✔✔1st
step catalyzed by cholesterol-7-a-hydroxylase
and is inhibited by bile acids
what must happen to bile acids before they leave the liver? - correct answer ✔✔conjugated to glycine or
taurine by amide bond = bile salts: glycoholic or taurocholic acid and glycochenodeoxycholic or
taurochenodeoxycholic acid
are bile salts or acids better emulsifiers? - correct answer ✔✔salts because they're deprotonated and
more amphipathic
What do intestinal bacterial do to the steroid nucleus? - correct answer ✔✔can remove glycine and
taurine and -OH from steroid nucleus, producing secondary bile salts
How are bile salts reabsorbed? - correct answer ✔✔reabsorbed through Na+-bile cotransported and
returned to blood (carried by albumin to liver) and reused (enterohepatic circulation)
What reduces bile salt reabsorption? - correct answer ✔✔bile acid sequestrants (promote poopin it out)
What is happening in cholelithiasis? - correct answer ✔✔cholesterol gallstone disease
more cholesterol enters bile than can be solubilized by available bile salts and PC
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