Lipid Metabolism Part IV Cholesterol & Lipoproteins Metabolism.

Question 1

For what in our body cholesterol is required and stored in?

Answer 1

it is required for membrane synthesis , steroid and vitamin D synthesis , and in liver bile acid synthesis , stored in tissues as cholesterol esters.

Question 2

most of cells derive there cholesterol from LDL or HDL, but if there any other way that cholesterol may be synthesized, if there what is it and where it occurs ?

Answer 2

cholesterol may be synthesized de novo and it occurs in liver, where as all carbons of cholesterol is synthesized/ derived from cytosolic acetyl-CoA in the cytoplasm by sequence of reactions.

Question 3

_______________ carries mitochondrial acetyl-CoA into cytoplasm.

Answer 3

citrate shuttle.

Question 4

Nicotinamide adenine dinucleotide phosphate (NADPH) is provided by_________.

Answer 4

Hexose monophosphate (HMP) shunt and malic enzyme.

Question 5

cholesterol is synthesized in most tissues of the body but it serves as a component of what and produced mainly in ?

Answer 5

component of cell membranes, produced in the liver and intestine.

Question 6

Cholesterol and cholesterol esters are transported throw what?

Answer 6

transported in blood lipoproteins.

Question 7

For cholesterol what is the major regulatory enzyme ?

Answer 7

Enzyme is 3-methyl-3hydroxy glutaryl CoA (HMG-CoA) reductase.

Question 8

In certain endocrine tissues, cholesterol is converted to _________.

Answer 8

steroid hormones.

Question 9

A cholesterol precursor can be converted to________________ and it is active from of

Answer 9

1,25-dihydroxycholecalciferol, the active form of vitamin D3.

Question 10

what is the major source of carbon for acetyl-CoA.

Answer 10

Glucose

Question 11

Cytosolic acetyl-CoA forms acetoacetyl-CoA, which condenses with another acetyl-CoA to form _____________.

Answer 11

HMG-CoA.

Question 12

Acetyl-CoA undergoes same reaction in mitochondrion, where HMG-CoA is used for____________

Answer 12

ketone body synthesis.

Question 13

Cytosolic HMG-CoA, a key intermediate in ________________, is reduced in the endoplasmic reticulum to mevalonic acid by the regulatory enzyme_____________.

Answer 13

biosynthesis, HMG-CoA reductase.

Question 14

_______________reductase is inhibited by cholesterol.

Answer 14

HMG-CoA reductase.

Question 15

In the liver, HMG-CoA reductase is also inhibited by ____________ and is induced when blood insulin levels are ______________.

Answer 15

bile salts, elevated.

Question 16

HMG-CoA reductase is also regulated by phosphorylation by the ______________ protein kinase.

Answer 16

AMP-activated protein kinase.

Question 17

______________acid is phosphorylated and decarboxylated to form the 5-carbon (C-5) isoprenoid, isopentenyl pyrophosphate.

Answer 17

Mevalonic acid

Question 18

Two isopentenyl pyrophosphate units condense, forming a C-10 compound forms?

Answer 18

geranyl pyrophosphate

Question 19

geranyl pyrophosphate, which reacts with another C-5 unit to form a C-15 compound produce?

Answer 19

farnesyl pyrophosphate.

Question 20

____________is formed from two C-15 units and then oxidized and cyclized, forming________________.

Answer 20

Squalene, lanosterol.