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?

<p>The change in free energy remains the same regardless of enzyme presence. (A)</p> Signup and view all the answers

Why are enzymes considered biological catalysts?

<p>They allow reactions to occur at lower activation energy. (C)</p> Signup and view all the answers

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

<p>The enzyme experiences a conformational shape change. (C)</p> Signup and view all the answers

What is the effect of competitive inhibitors on enzyme activity?

<p>They prevent the substrate from binding to the active site. (D)</p> Signup and view all the answers

How can the effects of an inhibitor be overcome?

<p>By increasing the amount of substrate present. (C)</p> Signup and view all the answers

At what point does denaturation of an enzyme typically occur?

<p>When the temperature exceeds an optimal level. (C)</p> Signup and view all the answers

What is the primary outcome of glycolysis?

<p>Conversion of glucose into two pyruvate molecules. (B)</p> Signup and view all the answers

What process produces ATP during the Calvin cycle?

<p>Substrate-level phosphorylation (A)</p> Signup and view all the answers

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

<p>It holds electrons and is used in the reduction phase of the Calvin cycle. (B)</p> Signup and view all the answers

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

<p>To generate ATP through ATP synthase. (B)</p> Signup and view all the answers

What initiates the light reactions of photosynthesis?

<p>Breakdown of water molecules (D)</p> Signup and view all the answers

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

<p>NADP+ (C)</p> Signup and view all the answers

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

<p>To generate a proton gradient (C)</p> 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?

<p>Two carbon dioxide (B)</p> Signup and view all the answers

What does ATP synthase do during oxidative phosphorylation?

<p>Synthesize ATP from ADP and inorganic phosphate (D)</p> Signup and view all the answers

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

<p>Mitochondrial matrix (A)</p> Signup and view all the answers

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

<p>NADH (B)</p> Signup and view all the answers

Flashcards

Gibbs Free Energy

The energy available to do work in a chemical reaction.

Endergonic Reaction

A chemical reaction that requires energy input to proceed. Products have more energy than reactants.

Exergonic Reaction

A chemical reaction that releases energy into the surroundings. Products have less energy than reactants.

Enzymes

Biological catalysts that speed up chemical reactions in living organisms.

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Active Site

The specific region on an enzyme where the substrate binds.

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Enzyme Conformational Change

An enzyme's shape changes upon binding to a substrate, like a hand closing around a pen. This change optimizes the reaction by positioning the substrate (pen) for interaction with the enzyme.

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Competitive Inhibitor

A molecule that binds to the active site of an enzyme, competing with the substrate for binding. This slows down the reaction rate.

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Non-competitive Inhibitor

A molecule that binds to an enzyme at a location other than the active site, causing a shape change that prevents the substrate from binding. This also slows down the reaction rate.

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Glycolysis

The breakdown of glucose into pyruvate, occurring in the cytosol of both prokaryotes and eukaryotes. It produces ATP, NADH, and pyruvate.

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Pyruvate Oxidation

The process of converting pyruvate into acetyl-CoA, which then enters the Krebs cycle. It occurs in the mitochondria.

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Citric Acid Cycle (Krebs Cycle)

A series of enzyme-catalyzed reactions that occurs in the mitochondrial matrix, breaking down acetyl-CoA into carbon dioxide, generating high-energy electron carriers (NADH and FADH2), and producing small amounts of ATP.

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Oxidative Phosphorylation

The process of using the energy stored in the electron carriers (NADH and FADH2) from previous stages to generate ATP. It involves two steps: electron transport chain and chemiosmosis.

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Electron Transport Chain

A series of protein complexes embedded in the inner mitochondrial membrane that transfer electrons, releasing energy to pump protons across the membrane, creating a proton gradient.

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Chemiosmosis

The process of using the proton gradient created by the electron transport chain to generate ATP by the enzyme ATP synthase.

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Substrate-level phosphorylation

In cellular respiration, ATP is made by using the energy released from breaking down molecules. This process, known as substrate-level phosphorylation, directly transfers a phosphate group from a substrate to ADP, forming ATP.

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Proton gradient in respiration

The electron transport chain uses the energy from electron movement to pump protons across a membrane, creating a proton gradient. This gradient is then used by ATP synthase to generate ATP.

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Photosystem 2

Photosystem 2 uses light energy to split water molecules, releasing oxygen and electrons. These electrons move down the electron transport chain, powering proton pumps to establish a proton gradient.

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Photosystem 1

Photosystem 1 captures light energy and energizes electrons, which are then passed to NADP+ to form NADPH. NADPH will be used in the Calvin cycle.

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Calvin cycle

The Calvin cycle uses the ATP and NADPH produced in the light reactions to convert carbon dioxide into glucose.

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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.

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