AP Biology Unit 3: Cellular Genetics

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Questions and Answers

What does a positive change in Gibbs free energy (Delta G) indicate about a reaction?

Energy must be absorbed for the reaction to occur. (correct)

The reaction releases energy spontaneously.

The reactants have higher free energy than the products. (correct)

The reaction is at equilibrium.

How do enzymes function in chemical reactions within the body?

They increase the Delta G of the reaction.

They permanently change the substrates to products.

They alter the pH of the reaction environment.

They reduce the activation energy required for the reaction. (correct)

Which of the following describes an endergonic reaction?

The products have less energy than the reactants.

It involves the breakdown of ATP.

It absorbs energy, resulting in a positive Delta G. (correct)

It occurs spontaneously without external energy.

What is true about the relationship between enzymes and Delta G?

The change in free energy remains the same regardless of enzyme presence. Signup and view all the answers

Why are enzymes considered biological catalysts?

They allow reactions to occur at lower activation energy. Signup and view all the answers

What occurs when a substrate binds to the active site of an enzyme?

The enzyme experiences a conformational shape change. Signup and view all the answers

What is the effect of competitive inhibitors on enzyme activity?

They prevent the substrate from binding to the active site. Signup and view all the answers

How can the effects of an inhibitor be overcome?

By increasing the amount of substrate present. Signup and view all the answers

At what point does denaturation of an enzyme typically occur?

When the temperature exceeds an optimal level. Signup and view all the answers

What is the primary outcome of glycolysis?

Conversion of glucose into two pyruvate molecules. Signup and view all the answers

What process produces ATP during the Calvin cycle?

Substrate-level phosphorylation Signup and view all the answers

Which of the following correctly describes the role of NADPH in photosynthesis?

It holds electrons and is used in the reduction phase of the Calvin cycle. Signup and view all the answers

What is the function of the proton gradient in the context of photosynthesis?

To generate ATP through ATP synthase. Signup and view all the answers

What initiates the light reactions of photosynthesis?

Breakdown of water molecules Signup and view all the answers

Which molecule serves as the final electron acceptor in the light reactions of photosynthesis?

NADP+ Signup and view all the answers

What is the primary role of the electron transport chain during oxidative phosphorylation?

To generate a proton gradient Signup and view all the answers

In the Krebs cycle, how many carbon dioxide molecules are produced per turn when breaking down one acetyl CoA?

Two carbon dioxide Signup and view all the answers

What does ATP synthase do during oxidative phosphorylation?

Synthesize ATP from ADP and inorganic phosphate Signup and view all the answers

Which of the following correctly identifies the location where the Krebs cycle takes place?

Mitochondrial matrix Signup and view all the answers

During the processes of glycolysis and the Krebs cycle, what is the major energy-rich product formed?

NADH Signup and view all the answers

Study Notes

Gibbs Free Energy

Gibbs free energy (ΔG) is the energy available to do work in a reaction.
ΔG = ΔH - TΔS, where ΔH is enthalpy (heat energy), T is temperature in Kelvin, and ΔS is entropy (disorder).
Reactions are either endergonic (absorb energy, ΔG is positive) or exergonic (release energy, ΔG is negative).
Endergonic example: ADP + inorganic phosphate → ATP (requires energy input).
Exergonic example: ATP → ADP + inorganic phosphate (releases energy).

Enzymes

Enzymes are biological catalysts that speed up reactions by lowering the activation energy.
They are proteins with specific shapes (primary, secondary, tertiary, quaternary structures) that bind substrates.
Enzyme-substrate binding causes a conformational shape change, allowing substrates to react.
Enzymes are not consumed in the reaction, meaning they can be reused.
Enzyme activity can be affected by inhibitors (competitive, non-competitive), temperature, pH, and salt concentration. Denaturation occurs at extreme temperatures or pH.

Cellular Respiration

Cellular respiration has three main steps: glycolysis, the Krebs cycle, and oxidative phosphorylation.
Glycolysis (cytoplasm): breaks down glucose (6C) into two pyruvate (3C) molecules, producing NADH and 2 ATP.
Krebs cycle (mitochondrial matrix): oxidizes acetyl CoA (2C), producing CO2, NADH, FADH2, and 1 ATP. One glucose molecule requires two turns of the cycle.
Oxidative phosphorylation (inner mitochondrial membrane): uses electron transport chain to create a proton gradient, then chemiosmosis to produce ATP; oxygen is the final electron acceptor.

Photosynthesis

Photosynthesis has two main stages: light-dependent reactions and the Calvin cycle.
Light-dependent reactions (thylakoid membrane): uses light energy to split water, generating oxygen, ATP, and NADPH.
Calvin cycle (stroma): uses CO2, ATP, and NADPH to produce glucose.
Cyclic electron flow produces ATP without NADPH. C₃ plants use 3-carbon intermediates; C₄ plants use 4-carbon intermediates to overcome photorespiration.

Additional Information

Inhibitors: competitive inhibitors compete for the active site; non-competitive inhibitors bind to a different site, altering the enzyme's shape.
Photosynthesis oxygen source: oxygen released during photosynthesis comes from water.
Different factors affect reaction rate, including temperature, substrate concentration, product concentration, and enzyme concentration.
Fermentation: an anaerobic process that regenerates NAD+, but produces less ATP than aerobic respiration.