Biochemistry Citric Acid Cycle Quiz

Coenzymes like FAD and FMN that can exist in three oxidation states, allowing them to participate in one-electron or two-electron transfer reactions.

Different forms of flavin coenzymes that represent different oxidation states. They are essential for many metabolic processes.

A coenzyme crucial for activating acyl groups for transfer by nucleophilic attack and for activating the α-hydrogen of the acyl group for abstraction as a proton.

Chemical bonds formed between the sulfhydryl group of CoA and acyl groups, enabling the activation and transfer of acyl groups.

A coenzyme that couples acyl-group transfer and electron transfer in the oxidation and decarboxylation of α-keto acids, found in important enzymes like pyruvate dehydrogenase and α-ketoglutarate dehydrogenase.

The negatively charged carbon atom of the carbanion formed by TPP binds to the carbonyl group of pyruvate, initiating the decarboxylation process.

The removal of a carboxyl group (COOH) from pyruvate, resulting in the formation of an acetylated TPP intermediate.

The positive charge on TPP stabilizes the negative charge created during decarboxylation, preventing the molecule from breaking down.

An intermediate formed after protonation of the acetylated TPP intermediate, crucial for subsequent reactions.

An enzyme responsible for transferring the acetyl group from the hydroxyethyl-TPP to lipoamide, forming acetyl-lipoamide.

A high-energy bond formed between the acetyl group and lipoamide, which is easily transferred to CoA.

An enzyme that oxidizes reduced lipoamide, regenerating FAD and producing NADH, essential for cellular respiration.

The lipoamide arm, attached to E2, is flexible and can move between the active sites of the pyruvate dehydrogenase complex, facilitating efficient substrate transfer.

A molecule that carries two-carbon units into the citric acid cycle. It is formed from pyruvate during oxidative decarboxylation.

A metabolic pathway that converts pyruvate into acetyl CoA by removing a carbon dioxide molecule and transferring electrons to NAD+.

A multi-enzyme complex responsible for catalyzing the oxidative decarboxylation of pyruvate. It consists of three enzymes (E1, E2, E3) and five coenzymes.

The first enzyme in the PDH complex, responsible for decarboxylation of pyruvate and transfer of the acetyl group to TPP.

The second enzyme in the PDH complex, transfers acetyl group from TPP to lipoamide and then to CoA.

The third enzyme in the PDH complex, oxidizes reduced lipoamide and transfers electrons to NAD+.

The five coenzymes are: TPP (thiamine pyrophosphate), Lipoamide, CoA (coenzyme A), FAD (flavin adenine dinucleotide), and NAD+ (nicotinamide adenine dinucleotide).

It links glycolysis to the citric acid cycle by converting pyruvate from glycolysis into acetyl CoA, which enters the citric acid cycle.

A central metabolic pathway that breaks down acetyl-CoA to produce energy, reducing equivalents (NADH and FADH2), and precursors for biosynthesis.

A metabolic pathway that functions in both catabolism (breaking down) and anabolism (building up) processes.

The first step is the condensation of acetyl-CoA with oxaloacetate to form citrate, catalyzed by the enzyme citrate synthase.

This reaction involves the condensation of acetyl-CoA and oxaloacetate to produce citrate and CoA.

The hydrolysis of the thioester bond in acetyl-CoA provides the energy for the reaction, making it exergonic.

The enzyme is allosterically inhibited by NADH, ATP, and succinyl-CoA.

Citrate synthase exhibits induced fit, where oxaloacetate binding causes a structural change in the enzyme, leading to the formation of the acetyl-CoA binding site, ensuring the correct order of substrate binding.

The mechanism of citrate synthase ensures that the reaction proceeds efficiently and prevents undesirable side reactions, contributing to the pathway's overall efficiency and metabolic control.

A molecule produced by mutations in isocitrate dehydrogenase, which alters DNA methylation patterns leading to gene expression changes and rapid cell growth.

A mitochondrial enzyme that normally synthesizes ketone bodies but in some cancers becomes phosphorylated, changing its activity to acetyltransferase, acetylation inhibits pyruvate dehydrogenase and facilitates the Warburg effect.

The metabolic shift in cancer cells, where they favor aerobic glycolysis (glucose breakdown) even in the presence of oxygen, instead of oxidative phosphorylation.

A lack of thiamine, a precursor of thiamine pyrophosphate (TPP), leads to insufficient activity of pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and transketolase, causing beriberi.

Mercury and arsenite inhibit pyruvate dehydrogenase complex activity by binding to dihydrolipoamide, disrupting cellular energy production and potentially causing neurological issues.

A complication of diabetes characterized by numbness, tingling, or pain in limbs due to damage to nerves, potentially caused by inhibition of pyruvate dehydrogenase complex.

A compound that counteracts arsenite poisoning by forming a complex with the arsenite, facilitating its removal from the body.

Hatmakers used mercury to make felt, which inhibited pyruvate dehydrogenase activity in the brain, leading to neurological issues and strange behavior.

Citrate has a tertiary alcohol group, making it difficult to oxidize directly. The tertiary alcohol group is converted to a secondary alcohol group in isocitrate, making it easily oxidizable.

Aconitase catalyzes the conversion of citrate to isocitrate by removing the pro-R hydrogen from the pro-R arm of citrate. This is a stereospecific reaction.

Aconitase, an iron-sulfur protein, utilizes a 4Fe-4S cluster in its active site. The iron cluster binds to the citrate molecule, facilitating the reaction.

Isocitrate dehydrogenase oxidizes the C-2 alcohol of isocitrate using NAD+ and simultaneously removes a carbon dioxide molecule (decarboxylation).

This complex, similar in structure and mechanism to pyruvate dehydrogenase, catalyzes the oxidative decarboxylation of alpha-ketoglutarate. It uses five coenzymes for its activity.

Succinyl-CoA Synthetase uses the hydrolysis of succinyl-CoA to drive the phosphorylation of GDP to GTP.

Succinyl-CoA Synthetase involves a series of phosphoryl transfer reactions. First, phosphate reacts with succinyl-CoA to form succinyl phosphate. Then, a histidine residue in the active site acquires the phosphate, forming a phosphohistidine intermediate. Finally, the phosphate is transferred to GDP, producing GTP.

There are two forms of Succinyl-CoA Synthetase, one uses ADP to produce ATP, while the other uses GDP to produce GTP. The ADP-using form is more prevalent in muscles with high energy needs.