Lipid Metabolism Vocabulary Flashcards

Vocabulary flashcards covering key terms, enzymes, and definitions from the lecture notes on lipid metabolism.

Lipids

Water-insoluble molecules that are highly soluble in organic solvents.

Saturated Fatty Acids

Monocarboxylic acids composed of an unbranched long-chain hydrocarbon containing $0$ double bonds.

Monounsaturated Fatty Acids

Fatty acids containing exactly $1$ double bond in their hydrocarbon chain.

Polyunsaturated Fatty Acids

Fatty acids containing $> 1$ double bond in their hydrocarbon chain.

Triacylglycerols

Neutral derivatives of glycerol esterified with three fatty acid chains that store approximately $7\times$ more energy per unit weight and volume than glycogen.

Apolipoproteins

Lipidless proteins expressed in liver or intestinal cells that package and transport hydrophobic lipids through the blood within lipoproteins.

Acyl-CoA Synthetase

An enzyme on the outer mitochondrial membrane that activates fatty acids for degradation by attaching Coenzyme A, spending $2$ ATP equivalents.

Carnitine Acyltransferase I (CAT-I)

An enzyme that transfers an acyl group from CoA to carnitine for transport across the inner mitochondrial membrane; inhibited by malonyl-CoA.

Carnitine Acyltransferase II (CAT-II)

An enzyme located in the mitochondrial matrix that converts acylcarnitine back into acyl-CoA and free carnitine.

$\beta$-Oxidation

A mitochondrial matrix pathway that degrades acyl-CoA by sequentially removing $2$ carbons from the carboxyl end per cycle through oxidation, hydration, oxidation, and cleavage.

Acyl-CoA Dehydrogenase

An inner mitochondrial membrane enzyme that catalyzes step 1 of $\beta$-oxidation, forming a double bond between the $\alpha$ and $\beta$ carbons and producing $\text{FADH}_2$.

Enoyl-CoA Hydrase

An enzyme in step 2 of $\beta$-oxidation that hydrates \text{trans-}\begin{equation*}\alpha,\beta\end{equation*}\text{-enoyl-CoA} to add a hydroxyl group to the $\beta$ carbon.

L-$\beta$-Hydroxyacyl-CoA Dehydrogenase

An enzyme in step 3 of $\beta$-oxidation that oxidizes the hydroxyl group at the $\beta$ carbon to a carbonyl group, producing $\text{NADH}$.

Thiolase

An enzyme (also called $\beta$-ketoacyl-CoA thiolase) that cleaves $\beta$-ketoacyl-CoA using Coenzyme A, yielding acetyl-CoA and an acyl-CoA shortened by $2$ carbons.

Enoyl-CoA Isomerase

An enzyme required during unsaturated fatty acid degradation to shift double bonds at odd-numbered positions from $\text{cis-}\\negmedspace\Delta^3$ to $\text{trans-}\\negmedspace\Delta^2$.

2,4-Dienoyl-CoA Reductase

An $\text{NADPH}$-dependent enzyme required during polyunsaturated fatty acid degradation to reduce double bonds at even-numbered carbon positions.

Propionyl-CoA

A 3-carbon fatty acyl-CoA molecule produced along with acetyl-CoA during the final cycle of $\beta$-oxidation of odd-numbered carbon fatty acids.

Ketone Bodies

Water-soluble fuel molecules (acetoacetate, acetone, and $\beta$-hydroxybutyrate) produced in liver mitochondria from excess acetyl-CoA when oxaloacetate levels are low.

$\beta$-Ketoacyl-CoA Transferase

An enzyme present in non-hepatic tissues but absent in the liver, allowing peripheral tissues to convert acetoacetate back into acetoacetyl-CoA for energy.

Citrate Shuttle

A mechanism that transports excess mitochondrial citrate into the cytoplasm, where citrate lyase converts it into acetyl-CoA and oxaloacetate for fatty acid synthesis.

Acetyl-CoA Carboxylase (ACC)

The rate-limiting, biotin-dependent cytosolic enzyme in fatty acid synthesis that catalyzes the ATP-dependent carboxylation of acetyl-CoA to form malonyl-CoA.

Acyl Carrier Protein (ACP)

A protein subunit of fatty acid synthase that anchors growing fatty acyl chains via a phosphopantetheine prosthetic group during biosynthesis.

Thioesterase (TE)

A domain of fatty acid synthase that recognizes the completed $C_{16}$-acyl group (palmitoyl-ACP) and releases palmitate via hydrolysis.

Isoprenoids

A diverse class of lipids built on repeating 5-carbon isoprene units.

HMG-CoA Reductase

The rate-limiting, $\text{NADPH}$-dependent cytosolic enzyme in cholesterol synthesis that catalyzes the conversion of HMG-CoA to mevalonate.

Statins

A class of cholesterol-lowering drugs (e.g., simvastatin, atorvastatin) that competitively inhibit HMG-CoA reductase by mimicking the structure of HMG-CoA.

Phosphatidate

A diacylglycerol 3-phosphate molecule formed from glycerol 3-phosphate and two fatty acyl-CoAs, serving as a common precursor for triacylglycerols and glycerophospholipids.

Glycerophospholipids

Polar membrane lipids consisting of a glycerol backbone, two fatty acid tails, a phosphate group, and a variable head group alcohol.