Citric Acid Cycle (Krebs Cycle) Summary

These flashcards cover key vocabulary and concepts related to the Citric Acid Cycle and its role in aerobic respiration, including important enzymes, regulation, and energy yields.

Citric Acid Cycle

A key metabolic pathway in aerobic respiration where acetyl-CoA is oxidized to produce ATP, NADH, FADH2, and CO2.

Acetyl-CoA

The primary reactant in the citric acid cycle, formed from pyruvate, that contributes acetyl groups for energy production.

Energy Yield from Citric Acid Cycle

Produces 3 NADH, 1 FADH2, and 1 ATP (or GTP) per acetyl-CoA molecule.

NADH

A coenzyme that carries high-energy electrons produced during the citric acid cycle and donates them to the electron transport chain.

FADH2

A coenzyme similar to NADH that carries electrons to the electron transport chain, produced during the citric acid cycle.

Electron Transport Chain (ETC)

A series of protein complexes in the mitochondrial membrane that transfer electrons from NADH and FADH2, producing ATP.

Oxidative Phosphorylation (OP)

The process where ATP is produced as electrons move through the ETC and O2 is reduced to H2O.

Substrate Level Phosphorylation

The generation of ATP by directly transferring a phosphate group to ADP in metabolic pathways.

Carbon Flow

The process in the citric acid cycle where carbon atoms are oxidized and released as CO2.

Citrate Synthase

An enzyme that catalyzes the reaction of acetyl-CoA and oxaloacetate to form citrate.

Isocitrate Dehydrogenase

An enzyme that converts isocitrate to alpha-ketoglutarate and produces NADH and CO2.

Alpha-Ketoglutarate Dehydrogenase

An enzyme that catalyzes the conversion of alpha-ketoglutarate to succinyl-CoA while generating NADH and CO2.

Succinyl-CoA Synthetase

An enzyme that converts succinyl-CoA to succinate and produces GTP or ATP in the process.

Fumarase

An enzyme that catalyzes the hydration of fumarate to malate in the citric acid cycle.

Malate Dehydrogenase

An enzyme that converts malate to oxaloacetate while producing NADH.

Overall Reaction of Citric Acid Cycle

Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 2 H2O → 2 CO2 + 3 NADH + FADH2 + GTP + CoA.

Regulation of Citric Acid Cycle

Regulated by the availability of acetyl-CoA and feedback mechanisms like NADH and ATP inhibition.

Pyruvate Dehydrogenase Complex

An enzyme complex that converts pyruvate into acetyl-CoA, utilizing cofactors like TPP, lipoic acid, and FAD.

Transport of Pyruvate

Pyruvate must cross the mitochondrial membranes via specific transport mechanisms for the citric acid cycle.

Cofactors in Citric Acid Cycle

Essential molecules like NAD+, FAD, CoA, and GDP that assist enzymes in reactions throughout the cycle.

Total ATP Yield

A total of approximately 12 ATP can be derived from one acetyl-CoA oxidized in the citric acid cycle.

Metabolic Hub

The citric acid cycle also serves as a connection point in other metabolic pathways, including fatty acid synthesis and amino acid metabolism.

Feedback Mechanisms

Regulatory processes that inhibit or activate pathways, affecting enzymes based on product levels in the citric acid cycle.

Acetyl Group

The two-carbon unit derived from acetyl-CoA used in the citric acid cycle.

Thioester Bond

A high-energy bond in acetyl-CoA that makes it a key substrate for the citric acid cycle.

Mitochondrial Matrix

The site within the mitochondria where the citric acid cycle occurs.

C6 Compounds

Refers to citrate which is a six-carbon compound formed at the start of the citric acid cycle.

NAD+

A coenzyme that acts as an electron carrier in metabolic reactions, accepting electrons to form NADH.

Pi

Inorganic phosphate, which is a substrate for ATP production in phosphorylation reactions.

Product Inhibition

A common regulatory mechanism where the end product of a pathway inhibits an enzyme involved in its production.

Transamination

The process wherein amino acids are converted to intermediates of the Krebs cycle, linking amino acid metabolism to energy production.