Bio1 10/26 Lecture: Cellular Respiration and Harvesting Energy (Part B)

Where does pyruvate oxidation occur, and where does pyruvate come from?

Pyruvate is transported from the cytoplasm, where glycolysis occurs, into the mitochondria for pyruvate oxidation.

What are the inputs and outputs of pyruvate oxidation?

Inputs: 2 pyruvates, 2 NAD⁺

Outputs: 2 CO₂, 2 acetyl CoA, 2 NADH

What does Acetyl CoA stand for?

Acetyal Coenzyme A

It is not actually an enzyme.

Is pyruvate oxidation aerobic or anaerobic? Is the citric acid cycle aerobic or anaerobic? Explain.

Both are aerobic because it relies on later steps in cellular respiration that do use oxygen—the ETC—though it does not directly use oxygen. They both require NAD⁺ (which is generated in the ETC) to make NADH.

What are the inputs and outputs of the citric acid cycle?

Inputs: 2 Acetyl CoA

• Optional (for exam) Inputs: 6 NAD⁺, 2 FAD, 2 ADP + P_i, 2 GDP, H₂O

Outputs: 4 CO₂, 6 NADH, 2 FADH₂, 2 ATP

Where does the citric acid cycle occur in eukaryotes versus prokaryotes?

In eukaryotic cells, the citric acid cycle takes place in the mitochondrial matrix.

In prokaryotic cells, the citric acid cycle takes place in the cytoplasm.

Why is the citric acid cycle a “cycle”?

The starting material, oxaloacetate (a four-carbon molecule), used at the beginning of the cycle is completely regenerated at the end of the citric acid cycle.

How many times does the citric acid cycle run per glucose molecule, and why?

The citric acid cycle operates twice per molecule of glucose processed in glycolysis because it operates once for each Acetyl CoA.

What is another name for the electron transport chain?

oxidative phosphorylation

Where does the ETC occur in eukaryotic cells versus prokaryotic cells?

In eukaryotic cells, the electron transport chain (ETC) occurs across the inner mitochondrial membrane.

In prokaryotic cells, the ETC occurs across the plasma/cell membrane.

What are the inputs and outputs of the electron transport chain?

Inputs: 10 NADH, 2 FADH₂, 28 ADP + P_i, 6 O₂

Output: 10 NAD⁺, 2 FAD, 28 ATP, 12 H₂O

Where does the energy in NADH and FADH₂ come from?

How is the energy stored in NADH and FADH₂ used in the ETC?

Their stored energy, originally derived from glucose, is used to establish a proton (H⁺) gradient across the inner mitochondrial membrane.

What happens to NAD⁺ and FAD produced by the ETC?

They are recycled and reused in glycolysis, pyruvate oxidation, and the citric acid cycle to produce more NADH and FADH₂.

What is the role of oxygen in the ETC? What is oxygen called in the ETC?

Oxygen accepts electrons at the end of the electron transport chain and combines with electrons and H⁺ to form water.

As such, oxygen is called the terminal electron acceptor.

What is the H⁺ gradient for in the electron transport chain? What is this process called (two names)?

H⁺ flows down its gradient through ATP synthase, providing the energy needed to produce ATP from ADP and P_i.

This process is called ATP synthesis, or chemiosmosis.

What happens to pyruvate oxidation, the citric acid cycle, and the ETC when oxygen is unavailable?

What is process happens instead? Describe it.

In the usual pathway of aerobic cellular respiration, the ETC cannot continue without oxygen. NAD⁺ regeneration is disrupted, so pyruvate oxidation and the citric acid cycle also stop as their required electron acceptors become unavailable.

Fermentation happens instead. Instead of producing any additional ATP or NADH, it regenerates NAD⁺ for glycolysis.