Biology Chapter 8: Metabolism and Energy

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Questions and Answers

What defines the specificity of an enzyme?

The presence of coenzymes or cofactors

The quantity of the substrate present

The amino acid sequence and three-dimensional shape of the enzyme (correct)

The temperature at which the reaction occurs

What is the term for the process that allows the enzyme to adjust its shape for better substrate interaction?

Enzyme stabilization

Induced fit (correct)

Active site remodeling

Substrate orientation

Which of the following statements about enzymes is incorrect?

Enzymes lower the activation energy required for reactions.

Enzymes can catalyze reactions in both directions.

Enzymes work best at a fixed temperature for all reactions. (correct)

Enzymes are not consumed in reactions.

What role do the R groups of amino acids play at the active site of an enzyme?

They catalyze the conversion of substrate to product. Signup and view all the answers

What primarily holds substrates in the active site of an enzyme?

Hydrogen and ionic bonds Signup and view all the answers

What is the significance of a negative ΔG in a chemical reaction?

It signifies that the reaction can perform maximum work and is exergonic. Signup and view all the answers

Which of the following correctly describes the role of ΔG in an endergonic reaction?

ΔG is positive and represents the energy needed to drive the reaction. Signup and view all the answers

What is the relationship between cellular respiration and photosynthesis regarding energy?

Photosynthesis is an endergonic reaction that requires energy, while cellular respiration is exergonic and releases energy. Signup and view all the answers

Why do cells maintain metabolic disequilibrium?

To constantly perform work by being open systems that flow materials in and out. Signup and view all the answers

How does the process of cellular respiration relate to free energy differences?

The huge free energy difference drives the series of reactions in respiration. Signup and view all the answers

What is the function of an enzyme in metabolic reactions?

To act as a catalyst that speeds up the rate of a reaction without being consumed. Signup and view all the answers

What represents the free energy of activation in a chemical reaction?

The amount of energy required to reach the transition state. Signup and view all the answers

Which mechanism underlies the action of enzymes in breaking down substrates like sucrose?

Enzymes lower the activation energy, allowing for quicker bond breakage. Signup and view all the answers

Why do some spontaneous reactions proceed very slowly at room temperature?

The energy of the reactants is not sufficient to reach the transition state. Signup and view all the answers

What happens when sufficient energy is absorbed by reactant molecules during a reaction?

Reactants enter an unstable transition state, allowing bond breaking. Signup and view all the answers

What happens to substrate binding at low concentrations?

An increase in substrate concentration speeds binding to available active sites. Signup and view all the answers

What is the effect of high substrate concentrations on enzyme reactions?

Active sites on all enzymes become engaged, leading to saturation. Signup and view all the answers

How does temperature influence enzyme activity?

Each enzyme has a specific optimal temperature for activity. Signup and view all the answers

What role do R groups in the active site play during enzymatic reactions?

They facilitate the transition-state formation of substrates. Signup and view all the answers

What leads to enzyme denaturation at elevated temperatures?

Thermal agitation disrupts weak bonds stabilizing the enzyme. Signup and view all the answers

Study Notes

Chapter 8: An Introduction to Metabolism

Metabolism is the sum total of an organism's chemical reactions, which transforms matter and energy, subject to the laws of thermodynamics. It's an emergent property of life.
Metabolic pathways are a series of defined steps that alter a specific molecule to produce a specific product. Each step is catalyzed by a specific enzyme.
Catabolic pathways break down complex molecules to simpler ones, releasing energy. Cellular respiration is a major catabolic pathway that breaks down glucose for energy (glucose + oxygen → carbon dioxide + water.)
Anabolic pathways, also known as biosynthetic pathways, consume energy to build complicated molecules from simpler ones. Examples include the synthesis of amino acids and proteins.
Energy released from catabolic pathways powers anabolic pathways.

Energy Transformations

Energy is the capacity to cause change. Kinetic energy is energy associated with motion (e.g., thermal energy); potential energy is energy that matter possesses due to its location or structure (e.g., light, chemical energy). Chemical energy is potential energy available for release in chemical reactions.
Thermodynamics studies energy transformations. An isolated system doesn't exchange energy or matter with its surroundings; an open system does. Organisms are open systems.
The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed.
The second law of thermodynamics states that every energy transfer or transformation increases the entropy (disorder) of the universe.
Spontaneity is the tendency of a process to occur without external influence. Spontaneous processes increase the entropy of the universe. An exergonic reaction is a spontaneous chemical reaction that releases free energy (negative ΔG), while an endergonic reaction is a nonspontaneous reaction requiring an energy input (positive ΔG). Reactions are reversible when at equilibrium (ΔG=0).

Enzymes

Enzymes are biological catalysts that speed up metabolic reactions by lowering the activation energy (EA) needed for a reaction, required for reactants to reach a transition state, without being consumed.
Enzymes are substrate specific, meaning they bind to specific substrates and their reaction occurs at a specific region: the active site.
Induced fit describes the change in shape of an enzyme as it binds to a substrate (interactions between chemical groups, resulting in a more favorable orientation for the reaction). This brings the active site's chemical groups into the optimal position to catalyze the reaction.

Enzymes and Metabolic Control

Metabolic enzymes are controlled via allosteric regulation, where a regulatory molecule binds at a site other than the active site, thus changing enzyme shape to either inhibit or stimulate its activity.
Feedback inhibition occurs when an end product of a metabolic pathway stops an earlier enzyme, preventing overproduction. Cells compartmentalize pathways to regulate metabolism.
Other regulatory mechanisms include the location of enzymes within membranes or organelles.

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Description

This quiz covers the fundamentals of metabolism including metabolic pathways, catabolic and anabolic processes, and energy transformations. Understand the intricacies of how organisms transform matter and energy while adhering to the laws of thermodynamics.