Cholesterol, Lipoprotein, and Steroid Metabolism – Review Flashcards

These fill-in-the-blank flashcards cover key structural features, metabolic pathways, regulatory mechanisms, clinical correlations, and transport processes related to cholesterol, bile acids, plasma lipoproteins, and steroid hormones.

Cholesterol is a structural component of all cell membranes and a precursor of __, steroid hormones, and vitamin D.

bile acids

The steroid nucleus of cholesterol is composed of __ fused hydrocarbon rings.

four

Steroids with a hydroxyl at C-3 and an 8–10 carbon side-chain at C-17 are called __.

sterols

Most plasma cholesterol exists in the more hydrophobic form known as __.

cholesteryl esters

All carbon atoms in cholesterol are provided by __.

acetyl-CoA

The rate-limiting step of cholesterol synthesis is the HMG-CoA reductase–catalyzed conversion of HMG-CoA to __.

mevalonate

HMG-CoA reductase activity is inhibited by phosphorylation via __.

AMP-activated protein kinase (AMPK)

Low intracellular sterol levels allow the SREBP-SCAP complex to move to the Golgi, releasing SREBP-2 that up-regulates __ expression.

HMG-CoA reductase

Statin drugs are competitive inhibitors of __.

HMG-CoA reductase

Because humans cannot oxidize the sterol nucleus to CO₂ and H₂O, cholesterol is eliminated mainly as __ or free cholesterol in bile.

bile acids/bile salts

The rate-limiting enzyme in bile acid synthesis is __.

7-α-hydroxylase

Before secretion, bile acids are conjugated with glycine or taurine to form fully ionized __.

bile salts

Greater than 95 % of bile salts are reabsorbed in the terminal ileum and returned to the liver via the __ circulation.

enterohepatic

A decrease in bile acids or excess cholesterol in bile can precipitate __ (gallstones).

cholelithiasis

Bile acid sequestrants (e.g., cholestyramine) lower plasma cholesterol by binding bile salts and relieving feedback inhibition on __ synthesis.

bile acid

The lipoprotein particles richest in triacylglycerol and lowest in protein are __.

chylomicrons

Apo B-48 is unique to __ and is required for their assembly.

chylomicrons

Apo C-II activates __, the enzyme that hydrolyzes TAG in chylomicrons and VLDL.

lipoprotein lipase (LPL)

Deficiency of LPL or apo C-II causes massive chylomicronemia known as type I __.

hyperlipoproteinemia (familial LPL deficiency)

VLDL particles are synthesized by the __ and are rich in endogenous TAG.

liver

Cholesteryl ester transfer protein (CETP) exchanges TAG from VLDL with __ from HDL.

cholesteryl esters

Progressive TAG loss converts VLDL to IDL and finally to __, which are cholesterol-rich.

LDL

LDL delivers cholesterol to peripheral tissues via receptor-mediated endocytosis that recognizes __ on LDL.

apo B-100

Familial hypercholesterolemia (type II) is most commonly due to defective or absent __ receptors.

LDL

Intracellular cholesterol inhibits its own synthesis by down-regulating HMG-CoA reductase and decreases further uptake by reducing __ synthesis.

LDL receptor

ACAT converts free cholesterol plus fatty acyl-CoA into storage form __.

cholesteryl ester

Oxidized LDL is taken up unregulated by macrophage SR-A receptors, forming cholesterol-laden __ cells.

foam

HDL supplies apo C-II and apo E to chylomicrons and VLDL and is the main particle involved in __ cholesterol transport.

reverse

Nascent HDL esterifies cholesterol using the plasma enzyme __ activated by apo A-I.

LCAT (lecithin:cholesterol acyltransferase)

HDL2 delivers cholesteryl esters to the liver via selective uptake mediated by receptor __.

SR-B1

Very low or absent HDL caused by ABCA1 deficiency is known as __ disease.

Tangier

High plasma levels of lipoprotein (a) [Lp(a)] increase coronary risk because apo(a) is structurally similar to __, interfering with clot breakdown.

plasminogen

The first and rate-limiting step in steroid hormone synthesis is conversion of cholesterol to pregnenolone by __ (P450scc).

cholesterol side-chain-cleavage enzyme (desmolase)

Transport of cholesterol from the outer to inner mitochondrial membrane is mediated by __ protein.

StAR (steroidogenic acute regulatory)

ACTH stimulates cortisol synthesis in the adrenal cortex via cAMP-mediated activation of cholesterol esterase and __ protein.

StAR

Aldosterone secretion is primarily stimulated by angiotensin II and a decreased plasma __ ratio.

Na⁺/K⁺

21-Hydroxylase deficiency impairs cortisol and aldosterone synthesis, leading to congenital __ hyperplasia.

adrenal

Steroid hormones exert their effects by binding intracellular receptors that interact with DNA sequences called __.

hormone-response elements (HREs)

Most steroid hormones circulate bound to specific carrier proteins; cortisol is mainly carried by __.

corticosteroid-binding globulin (transcortin)

Excess activity of PCSK9 increases degradation of LDL receptors and can cause autosomal-dominant __.

hypercholesterolemia

Plant sterols (phytosterols) lower plasma cholesterol because they reduce intestinal uptake through competition and re-export via __ transporters.

ABC (ATP-binding cassette) sterol

Ezetimibe lowers cholesterol by inhibiting intestinal cholesterol transporter __.

NPC1-L1

In fasting blood, VLDL cholesterol can be estimated by dividing plasma TAG by __.

5

Nonalcoholic fatty liver results from an imbalance between hepatic TAG synthesis and secretion of __ particles.

VLDL

The inverse relationship between plasma HDL concentration and atherosclerosis underlies HDL’s designation as the “__” cholesterol.

good