Biochemistry Chapter 8 Section 4

Questions and Answers

Define enzyme.

Enzymes are protein molecules that catalyze (i.e., increase the rates of) chemical reactions.

How does an enzyme speed up a reaction?

By lowering the activation energy required to begin the reaction.

What is activation energy?

The minimum energy required or the thermodynamic barrier that must be overcome for a reaction to take place.

The active site of an enzyme is the region that _____

is involved in the catalytic reaction of the enzyme. Signup and view all the answers

True or False: Enzymes lower the free energy of a reaction.

False Signup and view all the answers

Describe the substrate specificity of enzymes.

The active site of an enzyme is very specific to its substrates as it has a very precise shape, resulting in the ability to catalyze only certain reactions. Signup and view all the answers

What is meant by induced fit?

This model proposes that the initial interaction between enzyme and substrate is relatively weak, but these weak interactions rapidly induce conformational changes that strengthen binding. Signup and view all the answers

What local conditions affect enzyme activity?

pH, temperature, and the presence of cofactors and inhibitors. Signup and view all the answers

Magnesium, an essential trace element, functions as a ____ in DNA polymerase.

a cofactor necessary for enzyme activity. Signup and view all the answers

Define cofactor.

Non-protein helper required by the enzyme for catalytic activity. Signup and view all the answers

Define coenzyme.

An organic cofactor, such as vitamins. Signup and view all the answers

Describe competitive and non-competitive inhibitors.

Competitive inhibitors bind to the active site, while non-competitive inhibitors bind elsewhere, altering the enzyme's shape. Signup and view all the answers

How can the active site lower the activation energy?

During induced fit, the active site can cause stress on other parts of the enzyme, creating more potential energy. Signup and view all the answers

What theory supports the broad specificity of an enzyme?

The induced fit model explains how an enzyme may be able to bind to multiple substrates. Signup and view all the answers

How is activation energy usually supplied to a reaction?

As thermal energy from inter-molecular collisions or bond stretching vibrations. Signup and view all the answers

Define allosteric regulation.

Any case in which a protein's function at one site is affected by the binding of a regulatory molecule at a different site. Signup and view all the answers

How do cells regulate enzyme activity?

By controlling enzyme activity levels and the amount of enzyme produced. Signup and view all the answers

Define cooperativity.

The effect that the binding of one substrate has on the binding of another, impacting enzyme activity. Signup and view all the answers

Why is cooperativity considered allosteric?

Because binding of the substrate to one active site affects the catalysis of another active site. Signup and view all the answers

Define feedback inhibition.

A cellular control mechanism that inhibits a catalyzing enzyme when its substrate has accumulated to a certain level. Signup and view all the answers

True or False: By regulating enzyme activity, the cell can control its metabolism.

True Signup and view all the answers

Study Notes

Enzymes and Their Functions

Enzymes are proteins that act as catalysts to increase the rates of chemical reactions.
They lower the activation energy necessary for reactions, enabling them to proceed more quickly.
Enzymes do not alter the free energy change of a reaction; they only influence reaction speed.

Activation Energy

Activation energy (Ea or ΔG✳) is the minimum energy required to initiate a chemical reaction.
Example: In cellular respiration, 2 ATP are needed to convert glucose into pyruvic acid.

Active Site and Substrate Specificity

The active site is the part of the enzyme where the catalytic reaction occurs and is specifically shaped to fit its substrates.
Enzyme-substrate specificity emphasizes that only certain substrates can bind to an enzyme's active site, reminiscent of a "lock and key" model.

Induced Fit Model

This model suggests that initial interactions between an enzyme and substrate are weak, but these weak bonds induce conformational changes that enhance binding strength.

Factors Affecting Enzyme Activity

Optimal conditions for enzyme activity include a pH of 6-8 and a temperature range of 30-40 °C.
Enzyme activity can be influenced by the presence of cofactors, inhibitors, and denaturing conditions.

Cofactors and Coenzymes

Cofactors are non-protein molecules that assist enzymes in catalysis, which can be permanently or reversibly bound.
Coenzymes are specific types of organic cofactors, commonly derived from vitamins.

Inhibition Mechanisms

Competitive inhibitors resemble substrates and compete for the enzyme's active site.
Noncompetitive inhibitors bind elsewhere on the enzyme, changing its shape and hindering substrate binding or function.

Enzyme Regulation

Allosteric regulation describes how binding of a molecule affects protein function at a different site, potentially acting as either an inhibitor or activator.
Cells regulate enzyme activity through various methods including allosteric control, feedback inhibition, and enzyme synthesis regulation at the gene level.

Cooperativity

Cooperativity occurs when substrate binding to one active site influences the binding of another substrate.
Positive cooperativity enhances the affinity for subsequent substrate binding, while negative cooperativity decreases it.

Feedback Inhibition

This cellular control mechanism inhibits an enzyme when its product accumulates to a certain level, maintaining balance within the metabolic pathway.
Example: Dysregulation of feedback inhibition for insulin can lead to diabetes.

Conclusion

By regulating enzyme activity effectively, cells can maintain control over metabolic processes, ensuring proper levels of reactants and products.

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Explore the essential concepts of enzymes in this quiz. Learn how enzymes function and their role in catalyzing chemical reactions. Test your understanding of activation energy and the mechanisms that enable reactions to proceed more efficiently.