Enzymes and Cofactors Definition

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Questions and Answers

What is the primary role of enzymes in chemical reactions?

To completely change the nature of the substances involved

To serve as energy sources for reactions

To decrease reaction rates for safety

To increase reaction rates without being consumed (correct)

Which of the following statements about enzyme specificity is true?

Enzymes can work without any cofactors

Enzymes are not limited by the types of substrates they can bind

Each enzyme catalyzes a specific reaction (correct)

Enzymes can catalyze multiple different reactions simultaneously

Cofactors are essential for an enzyme's activity. Which of the following describes a cofactor?

A non-protein chemical compound or metallic ion (correct)

A byproduct of enzymatic reactions

An organic molecule that acts as a substrate

A protein that enhances enzyme activity

What distinguishes a prosthetic group from other coenzymes?

It is permanently bound to the enzyme Signup and view all the answers

What type of cofactors are inorganic ions classified under?

Inorganic ions Signup and view all the answers

Which group of enzymes has been categorized into six major classes?

All enzymes as a group Signup and view all the answers

Which of the following is a true statement regarding coenzymes?

They can change and behave as substrates Signup and view all the answers

How are many coenzymes obtained in the human diet?

From vitamins that the body cannot synthesize Signup and view all the answers

What role does a pocket complementary to the transition state (TS) play in enzyme function?

It reduces the activation energy. Signup and view all the answers

How do enzymes enhance reaction rates?

By binding the transition state better than either substrates or products. Signup and view all the answers

What happens if an enzyme binds the substrates too much?

The reaction would not proceed. Signup and view all the answers

What type of interactions stabilize the transition state during catalysis?

Multiple non-covalent interactions. Signup and view all the answers

What characteristic does the active site possess in relation to the transition state?

It is chemically complementary and sterically complementary to the transition state. Signup and view all the answers

In the induced fit model, what is required for optimal binding of the transition state?

The enzyme must change shape. Signup and view all the answers

Do enzymes change the concentrations of substrates and products in a reaction?

No, they do not change the concentrations of substrates and products. Signup and view all the answers

How does the shape of the enzyme change during the reaction process?

It adopts different conformations during substrate binding, catalysis, and release of products. Signup and view all the answers

What is true about the Gibbs free energy change (∆G) in relation to spontaneous reactions?

If ∆G equals 0, the reaction has reached equilibrium. Signup and view all the answers

Which statement accurately describes the role of enzymes in biochemical reactions?

Enzymes decrease activation energy but do not change ∆G. Signup and view all the answers

What term describes the specificity of enzymes based on multiple weak interactions with substrates?

Substrate specificity Signup and view all the answers

In enzyme classification, what does the term 'holoenzyme' refer to?

An enzyme that includes its cofactor. Signup and view all the answers

What factor is NOT part of the equation ∆G = ∆H – T∆S?

Activation energy (Ea) Signup and view all the answers

Which class of biomolecules do the majority of enzymes belong to?

Proteins Signup and view all the answers

Which of the following describes the term 'apoenzyme'?

An inactive enzyme without its necessary cofactor. Signup and view all the answers

How do coenzymes relate to vitamins in the context of enzymatic reactions?

Vitamins serve as precursors for coenzymes in metabolic processes. Signup and view all the answers

What is released from the enzyme at some point but can rebind later for another reaction?

Co-substrates Signup and view all the answers

What term describes the complete enzyme when it is combined with its cofactor or coenzyme?

Holoenzyme Signup and view all the answers

Which part of the enzyme is responsible for binding the substrate?

Active site Signup and view all the answers

What are the specific amino acids that make up the active site of an enzyme called?

Catalytic residues Signup and view all the answers

What must occur before a substrate can be converted into a product during a reaction?

The substrate must be bent to reach the transition state. Signup and view all the answers

If the activation energy is lower, what is the effect on the reaction rate?

The reaction is faster. Signup and view all the answers

What type of interactions facilitate the binding of the substrate at the active site?

Non-covalent interactions Signup and view all the answers

What is the relationship between substrate shape and the enzyme's active site for effective catalysis?

They should be complementary in structure. Signup and view all the answers

Study Notes

Enzymes: Definition and Characteristics

Enzymes are proteins that act as catalysts, increasing the rate of biochemical reactions without being consumed in the process.
Most enzymes catalyze reactions that either make or break covalent bonds.
Some enzymes act as transporters and use chemical energy, for example, breaking down ATP.
Each enzyme catalyzes only specific reactions.
There are six major classes of enzymes, grouped based on the type of reaction they catalyze.

Cofactors, Coenzymes, and Prosthetic Groups

Cofactors are non-protein chemical compounds or metallic ions required for the activity of an enzyme as a catalyst.
There are two types of cofactors: inorganic ions and complex organic molecules.
Inorganic ions are obtained through the diet, and many organic cofactors are derived from vitamins as they cannot be synthesized by humans.
Coenzymes are further divided into two types: prosthetic groups and co-substrates.
Prosthetic groups are coenzymes permanently bound to the enzyme, while co-substrates bind transiently. They are released from the enzyme at some point but then rebind for another reaction to occur.
Apoenzyme + cofactor (or coenzyme/prosthetic group) = holoenzyme.

Enzyme Catalysis: How do enzymes achieve catalysis?

Enzymes bind to their substrate(s) at the active site, which is made up of a few amino acids within the polypeptide chain called catalytic amino acids.
Non-covalent interactions facilitate this binding, based on the shape and chemical complementarity between the substrate(s) and the active site.
For a reaction to occur, energy is needed to reach the transition state, which is the intermediate stage between reactants and products. This energy is called activation energy.
The higher the activation energy, the slower the reaction proceeds.
Enzymes speed up reactions by stabilizing the transition state, making it easier to reach. This is done by binding the transition state better than either the substrates or the products.
If the enzyme binds too strongly to the substrates, the reaction would not proceed.
Similarly, if the enzyme binds too strongly to the products, they would not be released.
Stabilization occurs through multiple non-covalent interactions between the transition state and the enzyme. The active site is chemically and sterically complementary to the transition state.
The induce fit model describes how enzymes change shape to allow optimal binding of the transition state. As the enzyme binds the substrate(s), catalyzes the reaction, and releases products, it adopts different conformations.

Thermodynamics of Enzymes

Enzymes accelerate reactions but do not alter the equilibrium of a reaction, which is determined by the concentrations of substrates and products.
Enzymes do not change the standard free energy change (∆G°) of a reaction.
∆G = ∆H - T∆S
∆G is the free energy change, ∆H is the enthalpy change, T is the temperature, and ∆S is the entropy change.
If ∆G is less than zero, the reaction is spontaneous.
If ∆G is greater than zero, the reaction is not favored and requires energy.
If ∆G is equal to zero, the reaction has reached equilibrium.

Specificity of Enzymes

Multiple weak non-covalent interactions between the substrate(s) and enzyme provide the binding energy that contributes to catalysis and specificity.
These interactions are complementary to a specific substrate, meaning other molecules lack these interactions, resulting in substrate specificity.

Summary

Interactions between substrates and enzymes are optimized for a specific transition state.
The binding energy contributes to catalysis and specificity.

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Description

This quiz explores the definition and characteristics of enzymes, including their role as catalysts and the importance of cofactors and coenzymes. Understand how these elements facilitate biochemical reactions and their classifications. Test your knowledge on enzyme functions and the types of cofactors essential for their activity.