BIO40 Chapter 9

Write the balanced equation for cellular respiration

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat).

In cellular respiration, which reactant is oxidized and which is reduced?

Glucose is oxidized to CO2; oxygen is reduced to H2O.

How do anabolic and catabolic reactions relate to each other?

Catabolic reactions break down molecules and release energy that is used to drive anabolic reactions, which build complex molecules.

Why is ATP important in cells?

ATP is the cell’s main energy currency; it directly powers cellular work through phosphorylation and energy coupling.

Why is NADH important in cellular respiration?

NADH carries high-energy electrons to the electron transport chain for ATP production.

How are ATP and NADH different?

ATP provides immediate usable energy for cellular work, while NADH stores and transports high-energy electrons for later ATP production.

Where does glycolysis take place?

In the cytoplasm (cytosol) of the cell.

What are the inputs of glycolysis?

Glucose, 2 ATP, 2 NAD+, and ADP + Pi.

What are the outputs of glycolysis?

2 pyruvate, 2 NADH, net 2 ATP (4 produced, 2 used), and water.

Do aerobic or anaerobic conditions affect glycolysis directly?

No, glycolysis does not require oxygen and occurs under both aerobic and anaerobic conditions.

How is the first half of glycolysis different from the second half?

The first half (energy investment phase) uses 2 ATP to phosphorylate glucose; the second half (energy payoff phase) produces 4 ATP and 2 NADH.

What is substrate-level phosphorylation?

The direct transfer of a phosphate group from a substrate molecule to ADP to form ATP.

How is glycolysis regulated?

Primarily through feedback inhibition of key enzymes such as phosphofructokinase; high ATP inhibits glycolysis while high ADP or AMP stimulates it.

Does glycolysis occur in both eukaryotes and prokaryotes?

Yes, glycolysis is a universal pathway found in both eukaryotic and prokaryotic cells.

Why is phosphofructokinase considered a key regulatory enzyme?

It catalyzes a rate-limiting step and responds to cellular energy levels, controlling the pace of glycolysis.

What happens to pyruvate under anaerobic conditions?

It undergoes fermentation to regenerate NAD+, allowing glycolysis to continue.

What happens to pyruvate under aerobic conditions?

It is transported into the mitochondria and converted to acetyl-CoA for entry into the citric acid cycle.

Why must NAD+ be regenerated for glycolysis to continue?

NAD+ is required to accept electrons during glycolysis; without it, glycolysis would stop.

Define fermentation

An anaerobic pathway that allows ATP production to continue by regenerating NAD+ from NADH when oxygen is unavailable.

Why do cells use fermentation when oxygen is limited?

Because the electron transport chain cannot function without oxygen, so fermentation regenerates NAD+ to sustain glycolysis.

How does fermentation regenerate NAD+?

NADH transfers electrons to pyruvate or a derivative of pyruvate, converting NADH back to NAD+.

Why does fermentation not produce additional ATP beyond glycolysis?

Fermentation only regenerates NAD+; ATP is produced solely by substrate-level phosphorylation in glycolysis.

Describe lactic acid fermentation

Pyruvate is reduced to lactate by NADH, regenerating NAD+; occurs in muscle cells and some bacteria.

Describe alcoholic fermentation

Pyruvate is converted to ethanol and CO2, regenerating NAD+; occurs in yeast and some microorganisms.

What is the key difference between lactic acid and alcoholic fermentation?

Lactic acid fermentation produces lactate with no CO2 released; alcoholic fermentation produces ethanol and CO2.

How is fermentation different from aerobic respiration in ATP yield?

Fermentation yields only 2 ATP per glucose, while aerobic respiration yields much more (around 30–32 ATP).