Unit 3 Test Review Guide: Metabolism, Cellular Respiration, and Photosynthesis

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Q1. How do enzymes speed up metabolic reactions, and what is the effect of enzymes on activation energy?

Background

Topic: Enzyme Function and Activation Energy

This question tests your understanding of how enzymes act as biological catalysts, specifically how they lower the activation energy required for chemical reactions in cells.

Key Terms and Concepts:

Enzyme: A protein that speeds up chemical reactions in living organisms.
Activation Energy (Ea): The minimum amount of energy required to start a chemical reaction.
Substrate: The reactant that an enzyme acts upon.
Active Site: The region on the enzyme where the substrate binds.

Key Concept:

Enzymes lower the activation energy barrier, making it easier for reactions to occur.

Step-by-Step Guidance

Recall that every chemical reaction requires a certain amount of energy to get started, called the activation energy ().
Understand that enzymes work by binding to their specific substrate at the active site, forming an enzyme-substrate complex.
Recognize that this binding stabilizes the transition state and lowers the activation energy needed for the reaction to proceed.
Visualize or sketch a graph showing the energy profile of a reaction with and without an enzyme. Label the activation energy for both cases.
Think about how lowering the activation energy affects the rate of the reaction.

Try solving on your own before revealing the answer!

Final Answer:

Enzymes speed up metabolic reactions by lowering the activation energy barrier. They do this by binding to substrates and stabilizing the transition state, which reduces the amount of energy required for the reaction to proceed. On a graph, the activation energy for the enzyme-catalyzed reaction is lower than for the uncatalyzed reaction, resulting in a faster reaction rate.

Q2. How does substrate concentration affect the rate of an enzyme-catalyzed reaction?

Background

Topic: Enzyme Kinetics

This question examines how changing the amount of substrate influences the speed of reactions catalyzed by enzymes.

Key Terms and Concepts:

Substrate Concentration: The amount of substrate available for the enzyme to act upon.
Reaction Rate: The speed at which the product is formed.
Saturation: The point at which all enzyme active sites are occupied by substrate.

Step-by-Step Guidance

Recall that enzymes have a specific number of active sites where substrates can bind.
As substrate concentration increases, more active sites are occupied, and the reaction rate increases.
Consider what happens when all active sites are occupied (enzyme saturation).
Think about how the reaction rate changes before and after saturation is reached.

Try solving on your own before revealing the answer!

Final Answer:

As substrate concentration increases, the rate of an enzyme-catalyzed reaction increases until the enzyme becomes saturated. Once all active sites are occupied, increasing substrate concentration further does not increase the reaction rate; the rate levels off at a maximum value (Vmax).

Q3. What is the difference between competitive and noncompetitive (allosteric) inhibitors of enzymes?

Background

Topic: Enzyme Regulation

This question tests your understanding of how enzyme activity can be regulated by different types of inhibitors.

Key Terms and Concepts:

Competitive Inhibitor: A molecule that binds to the active site of an enzyme, blocking the substrate.
Noncompetitive (Allosteric) Inhibitor: A molecule that binds to a site other than the active site, changing the enzyme's shape and reducing its activity.
Active Site: The region of the enzyme where the substrate binds.
Allosteric Site: A site on the enzyme other than the active site, where regulatory molecules can bind.

Step-by-Step Guidance

Recall that competitive inhibitors resemble the substrate and compete for binding at the enzyme's active site.
Understand that noncompetitive inhibitors bind to a different (allosteric) site, not the active site.
Think about how each type of inhibitor affects the enzyme's ability to catalyze reactions.
Consider whether increasing substrate concentration can overcome the effects of each type of inhibitor.

Try solving on your own before revealing the answer!

Final Answer:

Competitive inhibitors bind to the active site and block substrate binding, but their effects can be overcome by increasing substrate concentration. Noncompetitive (allosteric) inhibitors bind to a different site, changing the enzyme's shape and reducing its activity regardless of substrate concentration.

Q4. What are the three main stages of cellular respiration, and where does each occur in the cell?

Background

Topic: Cellular Respiration Pathway

This question tests your knowledge of the stages of cellular respiration and their cellular locations.

Key Terms and Concepts:

Glycolysis: The first stage, breaking down glucose in the cytoplasm.
Krebs Cycle (Citric Acid Cycle): The second stage, occurring in the mitochondrial matrix.
Oxidative Phosphorylation (Electron Transport Chain): The third stage, occurring in the inner mitochondrial membrane.

Step-by-Step Guidance

Recall the names of the three main stages of cellular respiration.
Identify the location of glycolysis within the cell.
Determine where the Krebs Cycle takes place.
Locate where oxidative phosphorylation and the electron transport chain occur.

Try solving on your own before revealing the answer!

Final Answer:

The three main stages of cellular respiration are: Glycolysis (in the cytoplasm), Krebs Cycle (in the mitochondrial matrix), and Oxidative Phosphorylation/Electron Transport Chain (in the inner mitochondrial membrane).

Q5. What is the role of NADH and FADH2 in cellular respiration?

Background

Topic: Electron Carriers in Cellular Respiration

This question focuses on the function of electron carriers in transferring energy during cellular respiration.

Key Terms and Concepts:

NADH and FADH2: High-energy electron carriers produced during glycolysis and the Krebs cycle.
Electron Transport Chain (ETC): A series of proteins in the inner mitochondrial membrane that use electrons to produce ATP.
Oxidation/Reduction: Transfer of electrons from one molecule to another.

Step-by-Step Guidance

Recall that NADH and FADH2 are produced during earlier stages of cellular respiration.
Understand that these molecules carry high-energy electrons to the electron transport chain.
Think about what happens to the electrons once they reach the ETC.
Consider how the transfer of electrons is linked to ATP production.

Try solving on your own before revealing the answer!

Final Answer:

NADH and FADH2 carry high-energy electrons from glycolysis and the Krebs cycle to the electron transport chain, where their electrons are used to generate ATP through oxidative phosphorylation.

Q6. What are the reactants and products of photosynthesis?

Background

Topic: Photosynthesis Overview

This question tests your understanding of the overall chemical equation for photosynthesis.

Key Terms and Concepts:

Reactants: Substances used up in a chemical reaction.
Products: Substances produced by a chemical reaction.
Photosynthesis Equation:

Step-by-Step Guidance

Recall the basic formula for photosynthesis, including the number of molecules involved.
Identify the reactants (inputs) in the equation.
Identify the products (outputs) in the equation.
Think about the source of each reactant and the fate of each product.

Try solving on your own before revealing the answer!

Final Answer:

The reactants of photosynthesis are carbon dioxide (CO2), water (H2O), and light energy. The products are glucose (C6H12O6) and oxygen (O2).