أسئلة التاسعة بيو (قبل التعديل)

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Questions and Answers

What is the correct definition of a catalyst?

A type of enzyme that modifies the end product.

A molecule that decreases the activation energy of a reaction.

A substance that is consumed in a chemical reaction.

A substance that accelerates a chemical reaction without being changed. (correct)

What distinguishes complex (conjugated) protein enzymes from simple protein enzymes?

They have higher activation energies.

They generate more products during a reaction.

They contain a non-protein component called a cofactor. (correct)

They are composed entirely of amino acids.

Which type of cofactor is characterized by being loosely bound to an enzyme?

Holoenzyme

Coenzyme (correct)

Apo-enzyme

Prosthetic group

What happens during the enzymatic reaction when the substrate binds to the enzyme?

An activated intermediate enzyme-substrate complex is formed. Signup and view all the answers

What is a characteristic of a prosthetic group in enzyme function?

It is not an organic molecule. Signup and view all the answers

Which of the following statements is true regarding ribozymes?

They consist of RNA and act as catalysts. Signup and view all the answers

What is the role of the active site in an enzyme?

It is where substrate binding and the reaction occur. Signup and view all the answers

Which of the following is NOT a characteristic of coenzymes?

They are firm in their binding to enzymes. Signup and view all the answers

Which statement is true about the nature of enzymes?

All enzymes are proteins, except for ribozymes. Signup and view all the answers

What differentiates a coenzyme from a prosthetic group?

Coenzymes often derive from vitamins, while prosthetic groups do not. Signup and view all the answers

Which enzyme mechanism step occurs immediately after the formation of the enzyme-substrate complex?

The activated complex is cleaved to form products. Signup and view all the answers

Which of the following statements about enzyme stability is correct?

Coenzymes are thermo-labile while prosthetic groups are thermo-stable. Signup and view all the answers

Which characteristic is associated with the active site of an enzyme?

It is formed from specific amino acid sequences. Signup and view all the answers

Which statement regarding ribozymes is false?

Ribozymes are synthesized purely from proteins. Signup and view all the answers

What occurs first when a substrate interacts with an enzyme?

The substrate binds to the enzyme's active site. Signup and view all the answers

Which of the following statements about enzyme classification is accurate?

Enzymes can be classified as simple or complex based on their composition. Signup and view all the answers

What defines the term 'holoenzyme'?

A holoenzyme is the complete enzyme that includes both the protein part (apo-enzyme) and its non-protein components (cofactor). Signup and view all the answers

How do coenzymes differ from prosthetic groups in terms of binding to enzymes?

Coenzymes are loosely bound and can dissociate from the enzyme, while prosthetic groups are firmly attached and do not easily dissociate. Signup and view all the answers

What is the role of substrates in enzyme reactions?

Substrates are the reactants that bind to an enzyme's active site to form an enzyme-substrate complex. Signup and view all the answers

Can enzymes be classified based on their chemical nature, and if so, what are the two main types?

Yes, enzymes can be classified into simple protein enzymes and complex (conjugated) protein enzymes. Signup and view all the answers

Describe the enzyme action mechanism starting from substrate binding to product formation.

The substrate binds to the enzyme forming an enzyme-substrate complex, which then converts to products, releasing the original enzyme. Signup and view all the answers

Explain the concept of 'thermo-lability' in relation to coenzymes.

Thermo-lability refers to the sensitivity of coenzymes to heat, which can lead to their denaturation or loss of function. Signup and view all the answers

What characterizes the active site of an enzyme?

The active site is a restricted region of the enzyme where substrate molecules bind and undergo a chemical reaction. Signup and view all the answers

Identify one example of a coenzyme and one of a prosthetic group.

An example of a coenzyme is NAD, while a prosthetic group example is a metal ion like zinc (Zn). Signup and view all the answers

What is the complete term used to describe an enzyme that includes both its protein and non-protein components?

Holoenzyme Signup and view all the answers

What type of reaction mechanism occurs when a substrate binds to an enzyme and forms an activated enzyme-substrate complex?

Enzyme-substrate complex formation Signup and view all the answers

Name one method by which enzymes can be classified based on their composition.

Simple or complex based on whether they contain only protein or protein plus a non-protein part. Signup and view all the answers

What types of molecules can serve as cofactors for enzymes, and how are they characterized?

Cofactors can be organic coenzymes or inorganic prosthetic groups. Signup and view all the answers

What are the functions of an active site in an enzyme?

The active site is the region where the substrate binds and catalysis occurs. Signup and view all the answers

What distinguishes thermo-labile coenzymes from thermo-stable ones?

Thermo-labile coenzymes are sensitive to heat and can be denatured, while thermo-stable ones can withstand higher temperatures. Signup and view all the answers

Describe the role of substrates in enzyme catalyzed reactions.

Substrates act as reactants that bind to the enzyme to form the enzyme-substrate complex. Signup and view all the answers

How do ribozymes differ from traditional enzymes in terms of their chemical nature?

Ribozymes are RNA molecules, while traditional enzymes are typically proteins. Signup and view all the answers

What defines a holoenzyme?

The complete enzyme system including both protein and non-protein components Signup and view all the answers

Which statement about coenzymes is true?

They are organic molecules loosely associated with enzymes Signup and view all the answers

Which of the following statements is correct regarding substrate binding?

The substrate binds to the enzyme at the active site Signup and view all the answers

What is the role of cofactors in enzyme reactions?

They assist in enzyme activity but are not part of the enzyme structure Signup and view all the answers

Which characteristic distinguishes thermo-labile coenzymes from thermo-stable ones?

Thermo-labile coenzymes break down at high temperatures Signup and view all the answers

Which group is classified as inorganic cofactors?

Metal ions such as calcium and zinc Signup and view all the answers

What is the immediate product of the reaction S + E → ES?

Enzyme-Substrate Complex Signup and view all the answers

What best describes a substrate in an enzymatic reaction?

The molecule that forms an activated bond with the enzyme Signup and view all the answers

Study Notes

Biochemistry - Enzymes

Definition of Enzymes: Organic thermo-labile catalysts that accelerate chemical reactions without being consumed or affecting the final product.

Enzyme Classification

Simple Protein Enzymes: Composed solely of protein.
Complex (Conjugated) Protein Enzymes: Composed of:
- Protein part (apoenzyme): The protein component
- Non-protein component (cofactor): Can be a coenzyme or prosthetic group.
- The complete enzyme is called holoenzyme.

Enzyme Cofactors

Coenzymes: Organic, thermo-labile cofactors that bind loosely to the enzyme.
- Examples: Vitamins B derivatives (e.g., NAD, FAD).
Prosthetic Groups: Inorganic, thermo-stable cofactors that bind tightly to the enzyme.
- Examples: Metal ions (e.g., calcium (Ca), zinc (Zn)).

Effect of Heat on Enzymes

Heat affects the enzyme's activity by:
- causing the enzyme to become thermo-labile.
- loosely binding to a substrate.

Enzyme-Substrate Binding

Substrate: The reactant that binds to the enzyme.
Active (Catalytic) Site: The specific region of the enzyme where the substrate binds.
Mechanism:
- Substrate (S) binds to enzyme (E) forming an activated intermediate enzyme-substrate complex (ES)
- The activated complex (ES) cleaves to release products (P) and recreate the original enzyme (E) S + E <--> ES <--> E + P
Reaction steps:
- Substrate approaches the active site.
- Enzyme-substrate complex formation.
- Substrate's transformation into products.
- Release of products.
- Enzyme recycling.

Enzyme Binding Theories

Lock and Key Theory: The enzyme's active site has a fixed shape that complements the substrate's shape, fitting like a lock and key.
Induced Fit Theory: The enzyme's active site's shape changes slightly when the substrate binds, enabling a better fit and enhanced catalytic activity.

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Description

This quiz covers the essential concepts of enzymes in biochemistry, including their definitions, classifications, and the role of cofactors. Understanding how heat affects enzyme activity is also addressed. Test your knowledge of these fundamental biochemical catalysts!