Biochemistry Link Reaction and Krebs Cycle

Study Notes

Link Reaction

Necessary for converting pyruvate from glycolysis into a form usable in the Krebs cycle.
Occurs exclusively in the mitochondria of eukaryotic cells.

Link Reaction Process

Pyruvate molecules produced in glycolysis are transported into the mitochondrial matrix.
Pyruvate undergoes decarboxylation (removal of CO2) and oxidation, using NAD to form acetate.
The acetate combines with coenzyme A (CoA) to produce acetyl-CoA, which enters the Krebs cycle.
Reduced NAD formed in this reaction is later used to generate ATP.

Link Reaction Equation

Pyruvate + NAD + CoA → acetyl CoA + reduced NAD + CO2.

Krebs Cycle

Comprised of a series of oxidation-reduction reactions occurring in the mitochondrial matrix.
Involves the conversion of acetyl-CoA and oxaloacetate into citrate and back into oxaloacetate, regenerating key intermediates.

Krebs Cycle Steps

Acetyl-CoA (2C) combines with oxaloacetate (4C) to form citrate (6C).
Citrate undergoes decarboxylation and dehydrogenation to form a 5C compound, producing 1 NADH.
Further decarboxylation and dehydrogenation occurs, yielding 2 NADH, 1 FADH, and regenerating a 4C molecule.
ATP is generated through substrate-level phosphorylation, and the cycle restarts with a new acetyl-CoA.

Krebs Cycle Products

1 CoA is recycled back to the link reaction.
1 oxaloacetate is regenerated for further Krebs cycles.
2 CO2 are released as waste products.
1 ATP provides immediate energy for cellular activities.
3 NADH and 1 FADH participate in oxidative phosphorylation.
Yield from one glucose molecule is double the quantities above due to the production of 2 pyruvate per glucose.

Co-enzymes in Krebs Cycle

Co-enzymes are essential molecules that assist enzyme function.
Play critical roles in respiration and photosynthesis by transporting hydrogen atoms.
Key co-enzymes include NAD (most important for respiration), FAD (specific to Krebs cycle), and NADP (involved in photosynthesis).

Significance of the Krebs Cycle

Breaks down larger molecules into smaller components, converting pyruvate into carbon dioxide.
Produces hydrogen atoms used in the electron transport chain, fueling ATP production.
Regenerates the 4-carbon compound necessary for continuous operation of the Krebs cycle.
Supplies intermediate compounds essential for biosynthesis of critical molecules, such as fatty acids and chlorophyll.

Description

Test your knowledge on the link reaction and the Krebs cycle, essential processes in cellular respiration. This quiz will cover the conversion of pyruvate into acetyl-CoA and the series of reactions involved in the Krebs cycle. Dive into the details of these metabolic pathways and their significance in energy production.