Lipid and Cholesterol Metabolism Reactions

Vocabulary practice flashcards covering lipid and cholesterol metabolic pathways, key enzymes, stoichiometric reactions, and triacylglycerol structure and biological functions.

Triacylglycerols (triglycerides)

Lipids with a glycerol backbone esterified by three fatty acid chains ($\text{R}_1$, $\text{R}_2$, $\text{R}_3$, where $\text{R}$ = long-chain fatty acid) that serve the biological roles of providing energy storage, thermal insulation, and mechanical protection.

Malic enzyme

An enzyme that catalyzes the reversible oxidative decarboxylation reaction: $\text{Malate} + \text{NADP}^+ \rightleftharpoons \text{Pyruvate} + \text{CO}_2 + \text{NADPH} + \text{H}^+$.

ATP citrate lyase (citrate lyase)

An enzyme that catalyzes the reaction: $\text{Citrate} + \text{CoA} + \text{ATP} \rightarrow \text{Oxaloacetate} + \text{Acetyl-CoA} + \text{ADP} + \text{P}_i$.

Acetyl-CoA carboxylase (ACC)

A biotin-dependent enzyme that catalyzes the carboxylation reaction: $\text{Acetyl-CoA} + \text{HCO}_3^- + \text{ATP} \xrightarrow{\text{Biotin}} \text{Malonyl-CoA} + \text{ADP} + \text{P}_i$.

Ketoacyl synthase (KS / 3-ketoacyl-ACP synthetase)

An enzyme in fatty acid synthesis that catalyzes the condensation reaction: $\text{Acyl-ACP} + \text{Malonyl-ACP} \rightarrow \beta\text{-Ketoacyl-ACP} + \text{CO}_2 + \text{ACP}$.

Ketoacyl reductase (KR / 3-ketoacyl-ACP reductase)

An enzyme that catalyzes the reduction reaction: $\beta\text{-Ketoacyl-ACP} + \text{NADPH} + \text{H}^+ \rightarrow \text{D-}\beta\text{-hydroxyacyl-ACP} + \text{NADP}^+$.

Hydroxyacyl dehydratase (HD / 3-hydroxyacyl-ACP dehydratase)

An enzyme that catalyzes the dehydration reaction: $\text{D-}\beta\text{-hydroxyacyl-ACP} \rightarrow \text{trans-}\Delta^2\text{-enoyl-ACP} + \text{H}_2\text{O}$.

Enoyl(-ACP) reductase (ER)

An enzyme that catalyzes the reduction reaction: $\text{trans-}\Delta^2\text{-enoyl-ACP} + \text{NADPH} + \text{H}^+ \rightarrow \text{Acyl-ACP} + \text{NADP}^+$.

Synthesis of palmitate from acetyl-CoA only

The overall metabolic pathway equation: $8\,\text{Acetyl-CoA} + 7\,\text{ATP} + 14\,\text{NADPH} + 14\,\text{H}^+ \rightarrow \text{Palmitate} + 8\,\text{CoA} + 7\,\text{ADP} + 7\,\text{P}_i + 14\,\text{NADP}^+ + 6\,\text{H}_2\text{O}$.

Synthesis of palmitate from acetyl-CoA and malonyl-CoA

The overall metabolic pathway equation: $\text{Acetyl-CoA} + 7\,\text{Malonyl-CoA} + 14\,\text{NADPH} + 14\,\text{H}^+ \rightarrow \text{Palmitate} + 7\,\text{CO}_2 + 8\,\text{CoA} + 14\,\text{NADP}^+ + 6\,\text{H}_2\text{O}$.

HMG-CoA synthase

An enzyme in cholesterol synthesis that catalyzes the reaction: $\text{Acetoacetyl-CoA} + \text{Acetyl-CoA} + \text{H}_2\text{O} \rightarrow \beta\text{-Hydroxy-}\beta\text{-methylglutaryl-CoA (HMG-CoA)} + \text{CoA}$.

HMG-CoA reductase

An enzyme that catalyzes the NADPH-dependent reduction: $\text{HMG-CoA} + 2\,\text{NADPH} + 2\,\text{H}^+ \rightarrow \text{Mevalonate} + \text{CoA} + 2\,\text{NADP}^+$.

Prenyl transferase (first reaction)

The initial reaction catalyzed by prenyl transferase: $\text{Dimethylallyl-pyrophosphate} + \text{Isopenthenyl-pyrophosphate} \rightarrow \text{Geranyl-pyrophosphate} + \text{PP}_i$.

Prenyl transferase (second reaction)

The second reaction catalyzed by prenyl transferase: $\text{Geranyl-PP} + \text{Isopenthenyl-PP} \rightarrow \text{Farnesyl-PP} + \text{PP}_i$.

Squalene synthase

An enzyme that catalyzes the reductive condensation reaction: $2\,\text{Farnesyl-PP} + \text{NADPH} + \text{H}^+ \rightarrow \text{Squalene} + 2\,\text{PP}_i + \text{NADP}^+$.

Acyl-CoA:cholesterol acyltransferase (ACAT)

An enzyme that catalyzes the esterification reaction: $\text{Cholesterol} + \text{Fatty acyl-CoA} \rightarrow \text{Cholesteryl ester} + \text{CoA}$.