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Biochemistry

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Lipid

Question
12 out of 26
 

Which of the following is not true? (AIPG 2011)



A HDL is major determinant of cholesterol hemostasis

B High LDL is not associated with formation of foam cells

C HDL if low, LDL is not removed efficiently from circulation

D HDL has mechanism to prevent LDL oxidation

Ans. B High LDL is associated with formation of foam cells.

(Ref. Harper Biochemistry 28th/pg. 213)

a. HDL is major determinant of cholesterol hemostasis.

b. High LDL is associated with formation of foam cells.

c. HDL if low, LDL is not removed efficiently from circulation.

d. HDL has mechanism to prevent LDL oxidation.

LIPOPROTEINS

a. Atherosclerosis develops from LDL becoming oxidized (LDL-ox) by free radicals, particularly reactive oxygen species (ROS).

b. When oxidized LDL comes in contact with an artery wall, a series of reactions occur to repair the damage to the artery wall caused by oxidized LDL. The LDL molecule is globular shaped with a hollow core to carry cholesterol throughout the body. Cholesterol can move in the bloodstream only by being transported by lipoproteins.

c. The body's immune system responds to the damage to the artery wall caused by oxidized LDL by sending macrophages and T-lymphocytes to absorb the oxidized-LDL forming specialized foamcells. These white blood cells are not able to process the oxidized-LDL, and ultimately grow then rupture, depositing a greater amount of oxidized cholesterol into the artery wall. This triggers more white blood cells, continuing the cycle. Eventually, the artery becomes inflamed &blocked.

d. The first step of atherogenesis is the development of so called "fatty streaks," which are small sub-endothelial deposits of monocyte-derived macrophages. The primary documented driver of this process is oxidized Lipoprotein particles within the wall, beneath the endothelial cells, though upper normal or elevated concentrations of blood glucose also plays a major role and not all factors are fully understood. Fatty streaks may appear and disappear.

e. Low Density Lipoprotein particles in blood plasma, when they invade the endothelium and become oxidized creates a risk for cardiovascular disease. A complex set of biochemical reactions regulates the oxidation of LDL, chiefly stimulated by presence of enzymes, e.g. Lp-LpA2 and free radicals in the endothelium or blood vessel lining.

f. If the LDL-receptor activity is high, LDL particles should be removed efficiently; therefore, LDL-cholesterol levels should not increase to abnormally high.

g. HDL has also been shown to both prevent and reverse LDL oxidation.

h. HDL is the smallest and most dense lipoprotein, whereas chylomicrons and VLDLs are the largest and least dense lipoprotein particles.

i. A major function of HDL (scavenger of cholesterol) is to act as a repository for the apo C and apo E required in metabolism of chylomicrons and VLDL.

j. Approximately 70% of circulating LDL is cleared by LDL receptor–mediated endocytosis in the liver.

Lipoprotein

Maino Apo-lipoprotein

Function

Chylomicron

B48, AI, AII, E

Main transporter of ditary Triglyceride (from intestine to liver-exogenous cholesterol transporter)

LDL

B-100

Main cholesterol carrier in blood (endogenous cholesterol carrier to the peripheral tissue)

HDL

AI, AII

Transport cholesterol from peripheral tissue to liver for excretion, cardioprotective

Lipid Flashcard List

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