cholesterol

Question 1

cholesterol

Answer 1

-chole (bile) Stereos (solid): found in solid form in gallstones
-ubiquitous and essential component of animal cell membranes
-precursor of bile acids and many steroid hormones

Question 2

source of cholesterol

Answer 2

-diet: 200-300 mg per day
-De novo synthesis: 1 g per day
-produced in virtually all cells, but the liver is the major producer

Question 2

serious implications in human health bc of cholesterol

Answer 2

atherosclerosis- coronary artery disease and stroke

Question 3

chemical properties of cholesterol

Answer 3

-amphipathic molecule
-low solubility in water
-high concentration in plasma of healthy people (150-200mg/100mL)
- transported by lipoproteins as a free form or cholesterol ester

Question 3

synthesis of cholesterol

Answer 3

-synthesized from acetyl CoA in cytosol
-HMG CoA synthase in cytosol is involved in cholesterol synthesis, while the isoenzyme in the mitochondria is involved in ketogenesis
-cytosol does not have HMG CoA lyase activity

Question 4

two fates of HMG CoA

Answer 4

-HMG CoA to mevalonate through HMG CoA reductase
-HMG CoA to acetoacetate and acetyl CoA through HMG CoA lyase

Question 5

what converts HMG CoA to mevalonate? This is an _______

Answer 5

-HMG CoA reductase
-irreversible rate limiting step

Question 6

HMG CoA

Answer 6

-suppressed by cholesterol (feed back control)
-target of statins
-uses NADPH as a reducing cofactor

Question 7

statins

Answer 7

-competitive inhibitors for HMG CoA reductase (prescribed to lower plasma cholesterol levels)
-atrovastatin (lipitor)

Question 7

fates of cholesterol

Answer 7

-stored in the liver as cholesterol ester
-sent to other body parts
-converted to bile acids

Question 8

what is cholesterol used for in other body parts

Answer 8

-membrane components
-precursor for steroid synthesis

Question 9

cholesterol converted to bile acids?

Answer 9

-primary bile acids
-secondary bile acids; produced by microorganisms in the gut
-frequently conjugated via an amide bond to either glycine or taurine

Question 10

bile acids

Answer 10

-extra hydroxyl group and carboxyl groups (make bile acids amphipathic and called bile salts)
-secreted into bile, stored in gallbladder, then secreted into the small intestine

Question 11

what are emulsifying agents for dietary fats

Answer 11

-facilitate hydrolysis by pancreatic lipase
-facilitate the absorption of fat-soluble vitamins

Question 12

Which of the following reactions is the regulation point of cholesterol synthesis?
A. Conversion of acetyl CoA to acetoacetyl CoA
B. Synthesis of HMG-CoA
C. Reduction of HMG-CoA to mevalonate
D. Conversion of mevalonate to isopentenyl pyrophosphate
E. Ring closure of squalene 2,3-epoxide

Answer 12

C. reduction of HMG CoA to mevalonate

Question 13

plasma lipoproteins

Answer 13

-Complexes of proteins (apolipoproteins) and lipids that form distinct aggregates in plasma
-Transport lipids from tissue to tissue and participate in lipid metabolism
-Each class of lipoprotein has a characteristic apolipoprotein composition.
-Apolipoproteins serve as ligands for cell receptors.

Question 14

plasma lipoproteins are distinguished by their density differences

Answer 14

-High-density lipoproteins (HDL)
-Low-density lipoproteins (LDL)
-Intermediate-density lipoproteins (IDL)
-Very-low-density lipoproteins (VLDL)
-Chylomicrons

Question 15

structures of lipoproteins

Answer 15

-insoluble core: triacylglycerol and cholesterol ester
-amphipathic shell: phopholipids, cholerstol, apolipoproteins

Question 16

familial hypercholesterolemia inherited genetric condition

Answer 16

-Markedly elevated LDL cholesterol levels beginning at birth
-No feedback inhibition in de novo cholesterol synthesis
-Premature atherosclerosis and heart attacks

Question 17

familial hypercholesterolemia mutation in either LDL receptor or apoB100

Answer 17

-Little or no LDL receptor production
-Receptors are synthesized properly, but delivered to an improper location on
the membrane.
-Receptors have impaired binding affinity to LDL.
-Receptors can bind LDL, but cannot be internalized by endocytosis.