Cellular Respiration: Glycolysis and the Citric Acid Cycle

Flashcards covering the biochemical stages, chemical reactions, energy inputs, and outputs of glycolysis and the initial phase of the citric acid cycle based on the lecture transcript.

Stepwise oxidation of a carbon skeleton metabolite

The overarching process of cellular respiration where a carbon metabolite (glucose) is incrementally split and oxidized into organic acids and ultimately into carbon dioxide.

Carbon dioxide ($CO_2$)

The completely oxidized form of carbon that is generated during cellular respiration and released as a waste product.

Water ($H_2O$)

The completely oxidized form of hydrogen formed when harvested electrons give up their energy and attach to oxygen.

Electron transport chain

The metabolic stage dedicated to cashing in high-energy electrons harvested from glycolysis and the TCA cycle to generate ATP.

Cytosol

The cellular location within eukaryotic cells where glycolysis takes place.

Preparatory phase of glycolysis

The initial steps of glycolysis where the cell invests $2$ ATP molecules to add two phosphate groups and isomerize glucose before splitting it.

Fructose 1,6-bisphosphate

A six-carbon cyclized sugar intermediate with a carbon and a phosphate group extending from each side, which is split into two three-carbon sugars.

Triose

A biological sugar molecule containing three carbon atoms.

$$NAD^+$$

An electron carrier that picks up a pair of electrons along with a hydrogen atom to become $NADH$.

Glycolytic oxidation mechanism

An oxidation process occurring without molecular oxygen ($O_2$), where an oxygen atom from an inorganic phosphate oxidizes a carbonyl group into a carboxyl group on the carbon skeleton.

Pyruvate

A three-carbon organic acid that serves as the end product of glycolysis and the primary fuel input for the citric acid cycle.

Net yield of glycolysis

The net production resulting from glycolysis of one glucose molecule: $2$ pyruvate molecules, a net gain of $2$ ATP (spending $2$ and producing $4$), and $2$ $NADH$ molecules carrying non-oxidized electrons.

Mitochondria

The eukaryotic cell organelle where the citric acid cycle (TCA cycle) takes place.

Coenzyme A (CoA)

A metabolic helper molecule featuring a sulfhydryl group ($-SH$) that acts as a handle to hold and carry carbon fragments.

Acetyl CoA

A two-carbon acetyl group attached to coenzyme A, formed prior to entering the citric acid cycle.

Citrate (Citric acid)

A six-carbon tricarboxylic acid formed when a two-carbon acetyl group is combined with a four-carbon acceptor molecule in the first step of the citric acid cycle.

Isocitrate

A six-carbon isomer of citrate formed by shifting the position of a hydroxyl functional group to an adjacent carbon atom.

Succinyl CoA

A four-carbon intermediate bound to coenzyme A that marks the end of the decarboxylation phase of the citric acid cycle.

Decarboxylation phase

The first phase of the citric acid cycle (running from pyruvate entry through succinyl CoA formation) driven forward by the release of three $CO_2$ molecules and the reduction of $NAD^+$ to $NADH$.