Chapter 7: Cellular Respiration

What is the primary way all life produces ATP?

By harvesting electrons from glucose.

What are the two overall parts of cellular respiration?

Extracting energy from glucose into electron carriers and then using those electrons in an electron transport chain for ATP synthesis.

What happens to the energy-depleted carbons from glucose during cellular respiration?

They are released as CO2.

What molecule drives the electron transport chain process by functioning as an electron acceptor, and what is it converted into?

O2 drives the process and is converted into H2O.

What type of reactions involve the transfer of electrons between molecules in cellular respiration?

Oxidation-reduction (redox) reactions.

What is oxidation in the context of redox reactions?

An atom or molecule loses electrons.

What is reduction in the context of redox reactions?

An atom or molecule gains electrons.

What are the two main stages of glucose oxidation?

Glycolysis and the Krebs cycle.

Where does glycolysis occur in the cell?

In the cytoplasm.

What happens to glucose during glycolysis?

Glucose (6 carbons) is split in half to form two pyruvate molecules (3 carbons each).

What are the net products of glycolysis?

Some NADH and ATP, and two molecules of pyruvate.

Where does the Krebs cycle occur?

Within the mitochondrion.

What is produced during the Krebs cycle?

NADH, FADH2, and ATP.

How is NADH produced during glycolysis?

By a redox reaction where NAD+ gains electrons and a hydrogen ion (NAD+ + 2e- + H+ → NADH).

How is ATP produced during glycolysis?

By substrate-level phosphorylation, where an enzyme removes a phosphate from a high-energy substrate.

What happens to pyruvate before it can enter the Krebs cycle?

It undergoes pyruvate oxidation, where one of its three carbons is removed as CO2, NADH is formed, and the remaining 2-carbon fragment becomes acetyl-CoA.

Under what conditions does acetyl-CoA enter the Krebs cycle?

If there is insufficient ATP in the cell and oxygen is available.

What happens to acetyl-CoA if there is plentiful ATP?

It is diverted to fat synthesis for energy storage.

What are the main products of the Krebs cycle?

NADH, FADH2, ATP, and CO2.

After glycolysis and the Krebs cycle, what are the total energy carriers and ATP molecules generated from one glucose molecule exclusive of the electron transport chain?

4 ATP molecules, 10 NADH electron carriers, and 2 FADH2 electron carriers.

Where do NADH and FADH2 transfer their electrons?

To the electron transport chain, located in the inner mitochondrial membrane.

What is the function of many proteins in the electron transport chain?

They operate as proton pumps, pumping protons into the intermembrane space of the mitochondrion.

What is the role of oxygen in the electron transport chain?

Oxygen is the final electron acceptor, receiving electrons from the last transport protein to form water (H2O).

What is chemiosmosis, and how does it produce ATP?

Protons build up in the intermembrane space and then reenter the mitochondrial matrix via ATP synthase channels, with their passage powering the production of ATP from ADP.

What process occurs in the absence of oxygen to generate ATP?

Fermentation.

In fermentation, how does glycolysis continue despite the lack of oxygen?

Pyruvate or another molecule is used to oxidize NADH back into NAD+, allowing glycolysis to continue producing ATP.

What type of fermentation do eukaryotic cells like human muscle cells perform for short periods?

Lactic acid fermentation.

What are some practical applications of ethanol fermentation?

Used to produce food, alcohol, or health products.

How do fats provide energy for cells?

Fats are broken down into fatty acids, which then undergo -oxidation to convert them into acetyl-CoA, feeding into the Krebs cycle.

How do proteins provide energy for cells?

Proteins are broken down into amino acids, which undergo deamination reactions to convert them into molecules that can take part in the Krebs cycle.

Why are proteins not considered a great source of energy?

Deamination is energy-costly and results in toxic byproducts like ammonia.