Glycolysis and citric acid cycle

What is glycolysis?

A series of reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates.

Where does glycolysis take place?

In the cytosol (cytoplasm).

What is the first stage of cellular respiration?

Glycolysis.

Is glycolysis an ancient process?

Yes, glycolysis is an ancient process.

What type of process is glycolysis?

An anaerobic process that can occur with or without oxygen.

What happens to glucose during glycolysis?

A six-carbon glucose molecule is converted into two three-carbon pyruvate molecules.

How many ATP molecules are produced net during glycolysis?

2 ATP.

How many ATP molecules are used during glycolysis?

2 ATP.

How many ATP molecules are produced during the payoff phase?

4 ATP total.

What is the net ATP production of glycolysis?

2 ATP.

How many NADH molecules are produced during glycolysis?

2 NADH.

What happens to NAD+ during glycolysis?

NAD+ is converted to NADH.

Is carbon dioxide released during glycolysis?

No, no carbon is released as CO2 during glycolysis.

What are the two main phases of glycolysis?

The energy-requiring phase and the energy-releasing (payoff) phase.

What happens during the energy-requiring phase?

Glucose is rearranged, two phosphate groups are attached, and the modified sugar becomes unstable enough to split.

How many steps are in glycolysis?

10 steps.

How many steps are in the energy-requiring phase?

5 steps.

How many steps are in the energy-releasing phase?

5 steps.

What is hydrolysis?

A reaction in which a molecule is broken down using water.

What happens during the first key step of glycolysis?

ATP is converted to ADP through hydrolysis, resulting in glucose-6-phosphate.

What is glucose-6-phosphate?

Glucose modified by the addition of a phosphate group.

What is fructose 1,6-bisphosphate?

A six-carbon sugar with two phosphate groups attached.

How is fructose 1,6-bisphosphate formed?

Glucose is rearranged and two phosphate groups are attached using two ATP molecules.

Why are phosphate groups attached to glucose during glycolysis?

They make the modified sugar unstable, allowing it to split into two phosphate-bearing three-carbon sugars.

How many ATP molecules are used to form fructose 1,6-bisphosphate?

2 ATP.

What happens to fructose 1,6-bisphosphate?

It splits into two three-carbon phosphate isomers: glyceraldehyde-3-phosphate and DHAP.

What are the two three-carbon molecules formed when fructose 1,6-bisphosphate splits?

Glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).

What is G3P?

Glyceraldehyde-3-phosphate, a three-carbon sugar that enters the next phase of glycolysis.

What is DHAP?

Dihydroxyacetone phosphate, a three-carbon sugar that is an isomer of G3P.

What is an isomer?

A molecule that has the same molecular formula as another molecule but a different arrangement of atoms.

What happens to DHAP during glycolysis?

DHAP is converted spontaneously into G3P.

Why must DHAP be converted into G3P?

G3P is the form that can enter the next phase of glycolysis.

How many G3P molecules enter the payoff phase?

2 G3P molecules.

What happens during the energy-releasing (payoff) phase?

Each three-carbon G3P molecule is converted through a series of reactions into pyruvate.

How many times does the payoff phase occur?

Twice, once for each G3P molecule.

How many ATP molecules are produced during the payoff phase for each G3P?

2 ATP.

How many NADH molecules are produced during the payoff phase for each G3P?

1 NADH.

How many ATP molecules are produced during the payoff phase overall?

4 ATP.

How many NADH molecules are produced during the payoff phase overall?

2 NADH.

What is pyruvate?

A three-carbon molecule produced at the end of glycolysis.

What is the final product of glycolysis?

Two three-carbon pyruvate molecules.

What is the difference between anaerobic and aerobic respiration?

Anaerobic respiration does not require oxygen, while aerobic respiration requires oxygen.

Where does anaerobic respiration occur according to the notes?

In the cytosol (cytoplasm).

Where does aerobic respiration occur according to the notes?

In organelles such as the mitochondria.

Can glycolysis occur when oxygen is present?

Yes, glycolysis occurs whether oxygen is present or absent.

Why is glycolysis considered anaerobic?

It occurs in the cytoplasm and does not require oxygen.

What is the relationship between glycolysis and aerobic respiration?

Glycolysis is the first stage of aerobic respiration.

What is the relationship between glycolysis and anaerobic respiration?

Glycolysis is the first stage of anaerobic respiration.

What are the overall products of glycolysis?

2 pyruvate, 2 net ATP, and 2 NADH.

Where does the citric acid cycle occur in eukaryotic cells?

The mitochondrial matrix.

Where does the citric acid cycle occur in prokaryotic cells?

The cytoplasm.

What molecule enters the citric acid cycle?

Acetyl-CoA, produced from pyruvate oxidation.

What are the products of pyruvate oxidation?

Acetyl-CoA, NADH, and CO2.

What is substrate-level phosphorylation?

Direct transfer of a phosphate group from a phosphorylated substrate to ADP, producing ATP.

What is an isomer?

A molecule with the same molecular formula as another but a different arrangement of atoms.

What is ADP?

A two-phosphate molecule that can be converted into ATP.

What is GTP?

An energy-storing molecule similar to ATP, used in specific pathways such as protein synthesis.

What happens in Step 1 of the citric acid cycle?

Acetyl-CoA joins oxaloacetate to form citrate. CoA is released.

What happens in Step 2 of the citric acid cycle?

Citrate is rearranged into its isomer, isocitrate. No ATP or electron carriers are produced.

What happens in Step 3 of the citric acid cycle?

Isocitrate is oxidized into alpha-ketoglutarate. NADH and CO2 are produced.

What enzyme catalyzes Step 3?

Isocitrate dehydrogenase.

What happens in Step 4 of the citric acid cycle?

Alpha-ketoglutarate is oxidized into succinyl-CoA. NADH and CO2 are produced.

What enzyme catalyzes Step 4?

Alpha-ketoglutarate dehydrogenase.

What happens in Step 5 of the citric acid cycle?

Succinyl-CoA becomes succinate. Substrate-level phosphorylation produces ATP or GTP.

What happens in Step 6 of the citric acid cycle?

Succinate is oxidized into fumarate, producing FADH2.

What happens in Step 7 of the citric acid cycle?

Water is added to fumarate to form malate.

What happens in Step 8 of the citric acid cycle?

Malate is oxidized into oxaloacetate, producing NADH.

What molecule is regenerated at the end of each cycle?

Oxaloacetate.

What is the mnemonic for remembering the 8 intermediates?

Can I Keep Selling Seashells for Money, Officer.

What are the 8 intermediates in order?

Citrate, Isocitrate, Alpha-ketoglutarate, Succinyl-CoA, Succinate, Fumarate, Malate, Oxaloacetate.

What are the products of one turn of the citric acid cycle?

3 NADH, 1 FADH2, 1 ATP or GTP, and 2 CO2.

What are the products of two turns of the citric acid cycle?

6 NADH, 2 FADH2, 2 ATP or GTP, and 4 CO2.

Why does the citric acid cycle produce NADH and FADH2?

They carry high-energy electrons to the electron transport chain for oxidative phosphorylation.

How does NADH contribute to ATP production?

It delivers electrons to Complex I of the ETC, helping drive proton pumping and ATP synthesis.

How does the proton gradient produce ATP?

H+ flows through ATP synthase, driving ATP production by chemiosmosis.

Does the citric acid cycle directly use oxygen?

No. Oxygen is the final electron acceptor in the ETC.

Why does the citric acid cycle depend indirectly on oxygen?

Oxygen allows NADH and FADH2 to be oxidized back into NAD+ and FAD for reuse.

What happens to oxygen at the end of the ETC?

It accepts electrons and combines with H+ to form water.

How many enzyme-catalyzed reactions occur in the citric acid cycle?

Eight reactions, each catalyzed by an enzyme.

What is the main purpose of the citric acid cycle?

To harvest energy from acetyl-CoA by producing NADH and FADH2 for oxidative phosphorylation.