Study Guide: Bioenergetics, Enzymes, and Cellular Metabolism

Q1. For a thermodynamically favorable (spontaneous) chemical reaction: Is the change in Gibbs free energy positive or negative? Do the reactants have more or less free energy than the products? Is this reaction endergonic or exergonic? Is this reaction necessarily fast?

Background

Topic: Thermodynamics in Biology

This question tests your understanding of Gibbs free energy ($\Delta G$), spontaneity, and the difference between exergonic and endergonic reactions. It also asks you to consider the relationship between thermodynamic favorability and reaction rate.

Key Terms and Concepts:

• Gibbs Free Energy ($\Delta G$): A measure of the usable energy in a system that can do work at constant temperature and pressure.

• Exergonic Reaction: Releases free energy ($\Delta G < 0$).

• Endergonic Reaction: Requires input of energy ($\Delta G > 0$).

• Spontaneous Reaction: Occurs without input of energy (thermodynamically favorable).

Step-by-Step Guidance

1. Recall that a spontaneous reaction is one that is thermodynamically favorable. Think about what sign $\Delta G$ must have for a reaction to be spontaneous.

2. Consider the relationship between the free energy of reactants and products. For a reaction to be spontaneous, does the system lose or gain free energy?

3. Determine whether the reaction is exergonic or endergonic based on the sign of $\Delta G$.

4. Think about whether a spontaneous reaction is always fast. What other factor (besides $\Delta G$) determines the rate of a reaction?

Try solving on your own before revealing the answer!

Q2. Define catabolism and anabolism. Which process is endergonic and which is exergonic? What links catabolism and anabolism?

Background

Topic: Metabolic Pathways

This question tests your understanding of the two main types of metabolic pathways and how energy transfer is managed in cells.

Key Terms:

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy.

• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input.

• ATP: The main energy currency that links catabolic and anabolic reactions.

Step-by-Step Guidance

1. Define catabolism and anabolism in your own words, focusing on whether they build up or break down molecules.

2. Identify which process is exergonic (releases energy) and which is endergonic (requires energy input).

3. Think about how the energy released from catabolism is used to drive anabolism. What molecule acts as the energy shuttle?

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Q3. How do enzymes affect the change in free energy ($\Delta G$) of a reaction? How do enzymes affect the activation energy ($E_A$) of a reaction?

Background

Topic: Enzyme Catalysis

This question tests your understanding of how enzymes influence the energetics of biochemical reactions.

Key Terms and Formulas:

• Activation Energy ($E_A$): The energy barrier that must be overcome for a reaction to proceed.

• Gibbs Free Energy Change ($\Delta G$): The difference in free energy between reactants and products.

Step-by-Step Guidance

1. Recall what $\Delta G$ represents in a chemical reaction and whether enzymes can change this value.

2. Think about the role of enzymes in lowering the activation energy ($E_A$) and how this affects the reaction rate.

3. Consider whether enzymes make a reaction more or less thermodynamically favorable, or simply make it happen faster.

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Q4. Name three characteristics of enzymes and three things that can affect enzyme activity.

Background

Topic: Enzyme Structure and Function

This question tests your knowledge of enzyme properties and the factors that influence their activity.

Key Terms:

• Enzyme: A biological catalyst that speeds up chemical reactions without being consumed.

• Factors Affecting Activity: Temperature, pH, substrate concentration, inhibitors, etc.

Step-by-Step Guidance

1. List three general properties or characteristics of enzymes (e.g., specificity, reusability, etc.).

2. Identify three environmental or chemical factors that can influence how well an enzyme works.

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Q5. Draw a diagram that couples photosynthesis to respiration. Include the small molecules that link these two processes.

Background

Topic: Energy Flow in Cells

This question tests your understanding of how photosynthesis and cellular respiration are interconnected, especially through the exchange of molecules like $CO_2$, $O_2$, glucose, and water.

Key Terms:

• Photosynthesis: The process by which plants convert light energy into chemical energy (glucose).

• Cellular Respiration: The process by which cells break down glucose to produce ATP.

• Linking Molecules: $CO_2$, $O_2$, $H_2O$, glucose.

Step-by-Step Guidance

1. Sketch or visualize the overall flow: Photosynthesis produces glucose and $O_2$; respiration uses glucose and $O_2$ to produce $CO_2$ and $H_2O$.

2. Label the small molecules that are exchanged between the two processes.

3. Indicate the direction of energy flow (light energy in, ATP out).

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Q6. Give the balanced equation for the complete oxidation of glucose via cellular respiration (without accounting for ATP production). What substance is being oxidized? What substance is being reduced?

Background

Topic: Cellular Respiration

This question tests your ability to write the overall chemical equation for aerobic respiration and identify redox changes.

Key Terms and Formulas:

• Oxidation: Loss of electrons (or hydrogen).

• Reduction: Gain of electrons (or hydrogen).

• Glucose Oxidation Equation:

  $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$

Step-by-Step Guidance

1. Write the balanced equation for the complete oxidation of glucose.

2. Identify which molecule loses electrons (is oxidized) and which gains electrons (is reduced).

3. Remember that oxygen is the final electron acceptor in aerobic respiration.

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Q7. What are the “inputs” and “outputs” of glycolysis, pyruvate oxidation, and the citric acid cycle?

Background

Topic: Cellular Metabolism

This question tests your knowledge of the main reactants and products of the three major stages of cellular respiration.

Key Terms:

• Glycolysis: Glucose breakdown in the cytoplasm.

• Pyruvate Oxidation: Conversion of pyruvate to acetyl-CoA.

• Citric Acid Cycle: Series of reactions that generate electron carriers.

Step-by-Step Guidance

1. List the main input and output molecules for glycolysis (e.g., glucose, pyruvate, ATP, NADH).

2. Do the same for pyruvate oxidation (e.g., pyruvate, acetyl-CoA, NADH, $CO_2$).

3. List the inputs and outputs for the citric acid cycle (e.g., acetyl-CoA, $CO_2$, NADH, FADH2, ATP/GTP).

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Q8. Give the balanced equation for the photosynthetic production of glucose. What substance is being oxidized? What substance is being reduced?

Background

Topic: Photosynthesis

This question tests your ability to write the overall equation for photosynthesis and identify the redox changes involved.

Key Terms and Formulas:

• Photosynthesis Equation:

  $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

• Oxidation/Reduction: Identify which reactant is oxidized and which is reduced.

Step-by-Step Guidance

1. Write the balanced equation for the production of glucose via photosynthesis.

2. Determine which molecule loses electrons (is oxidized) and which gains electrons (is reduced).

3. Remember that water is split and oxygen is released during photosynthesis.

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Q9. Explain how chemiosmosis links the electron transport chain and ATP synthesis by mitochondria.

Background

Topic: Oxidative Phosphorylation

This question tests your understanding of how the electron transport chain creates a proton gradient that drives ATP synthesis.

Key Terms:

• Chemiosmosis: The movement of protons across a membrane, generating ATP.

• Electron Transport Chain (ETC): Series of protein complexes that transfer electrons and pump protons.

• ATP Synthase: Enzyme that synthesizes ATP using the proton gradient.

Step-by-Step Guidance

1. Describe how electrons move through the ETC and how this movement is coupled to proton pumping.

2. Explain how the resulting proton gradient represents stored energy.

3. Describe how protons flow back through ATP synthase, driving the production of ATP.

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Q10. What is the role of fermentation in the absence of oxygen and name two products of fermentation.

Background

Topic: Anaerobic Metabolism

This question tests your understanding of how cells generate energy when oxygen is not available and the types of fermentation products formed.

Key Terms:

• Fermentation: Metabolic process that regenerates NAD+ from NADH, allowing glycolysis to continue in the absence of oxygen.

• Common Products: Lactic acid, ethanol, $CO_2$.

Step-by-Step Guidance

1. Explain why fermentation is necessary when oxygen is not present.

2. List two common products of fermentation in different organisms (e.g., lactic acid in animals, ethanol in yeast).

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Q11. Be able to draw or label a mitochondrion or chloroplast, identifying key structures and the location of various metabolic processes.

Background

Topic: Organelle Structure and Function

This question tests your ability to recognize and label the main structures of mitochondria and chloroplasts, and to associate them with specific metabolic processes.

Key Terms:

• Mitochondrion: Outer membrane, inner membrane, cristae, matrix.

• Chloroplast: Outer membrane, inner membrane, thylakoid, stroma, grana.

• Metabolic Processes: Glycolysis, citric acid cycle, electron transport chain, light reactions, Calvin cycle.

Step-by-Step Guidance

1. Draw or find a diagram of a mitochondrion and label the outer membrane, inner membrane, cristae, and matrix.

2. Indicate where the citric acid cycle and electron transport chain occur.

3. Repeat for a chloroplast: label the outer membrane, inner membrane, thylakoid, grana, and stroma.

4. Indicate where the light reactions and Calvin cycle occur.

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Q12. List three pieces of evidence that mitochondria and chloroplasts were originally free-living prokaryotes that were engulfed by an ancestral eukaryote (endosymbiotic theory).

Background

Topic: Endosymbiotic Theory

This question tests your understanding of the evidence supporting the idea that mitochondria and chloroplasts originated as independent prokaryotic organisms.

Key Terms:

• Endosymbiotic Theory: The hypothesis that mitochondria and chloroplasts evolved from prokaryotes engulfed by ancestral eukaryotic cells.

• Evidence: DNA, ribosomes, double membranes, etc.

Step-by-Step Guidance

1. List three features of mitochondria and chloroplasts that are similar to prokaryotes (e.g., their own DNA, ribosomes, reproduction by binary fission).

2. Explain briefly how each feature supports the endosymbiotic theory.

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