Enzymes: Biological Catalysts and Structure

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Questions and Answers

What is the primary effect of competitive inhibition on enzyme activity?

Enzyme's active site becomes permanently occupied

Inhibitor permanently alters the enzyme structure

Inhibitor enhances the reactivity of the substrate

Enzyme activity is temporarily blocked by a substance similar to the substrate (correct)

Which of the following statements is true regarding non-competitive inhibitors?

Competitive inhibitors can also be classified as non-competitive inhibitors.

They bind irreversibly to the active site of an enzyme.

Non-competitive inhibition leads to permanent denaturation of all enzymes.

They may bind to allosteric sites and affect enzyme activity. (correct)

How does increasing the concentration of substrate affect competitive inhibition?

It reduces the effectiveness of competitive inhibitors. (correct)

It has no effect on the enzyme's activity.

It causes irreversible damage to the enzyme.

It enhances binding of the competitive inhibitors to the enzyme.

Which of the following molecules is an example of a competitive inhibitor?

Malonate Signup and view all the answers

What is a common characteristic of competitive inhibitors compared to substrates?

They are structurally similar but not identical to the substrate. Signup and view all the answers

What mechanism do reversible non-competitive enzyme inhibitors use to affect enzyme activity?

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

Which of the following is NOT a characteristic of irreversible non-competitive enzyme inhibitors?

They bind only to the active site. Signup and view all the answers

How does feedback inhibition function in metabolic pathways?

End products inhibit their own synthesis by binding to enzymes. Signup and view all the answers

Which enzyme classification group is involved in oxidation-reduction reactions?

Oxidoreductases Signup and view all the answers

What is a common consequence of heavy metal ions on enzymes?

They break disulphide bridges within the enzyme. Signup and view all the answers

Which statement about cyanides as enzyme inhibitors is true?

They permanently alter the enzyme's active site. Signup and view all the answers

In the context of enzyme regulation, what does an allosteric site refer to?

A site where regulatory molecules can bind and affect enzyme activity. Signup and view all the answers

What type of enzyme inhibitors do cyanides and heavy metal salts exemplify?

Irreversible non-competitive inhibitors Signup and view all the answers

Which of the following describes a function of the enzyme threonine in feedback inhibition?

It binds to the allosteric site of enzyme 1 to inhibit activity. Signup and view all the answers

Which of the following enzyme classifications is primarily involved in the breaking down of large molecules into smaller ones?

Lyases Signup and view all the answers

Study Notes

Enzymes: Biological Catalysts

Enzymes are biological polymers that catalyze biochemical reactions.
Enzymes speed up biochemical reactions without being consumed.
All enzymes are globular proteins, typically made of one or more polypeptides.
Ribozymes are enzymes composed of RNA, found in ribosomes (e.g., peptidyl transferase).

Enzyme Structure: Active Site

The catalytic activity of an enzyme is located in its active site, a specific three-dimensional cavity.
The active site is a small region of the enzyme.
Substrate molecules bind to the active site via non-covalent interactions (e.g., hydrogen bonds).
Active sites contain amino acids that participate in both substrate binding and catalysis.
A binding site is the area on the enzyme that holds the substrate.
A catalytic site is the area on the enzyme where a reaction occurs to transform the substrate.
The shape of the active site is crucial in substrate specificity, allowing only a particular substrate to bind.

Enzyme Cofactors

Some enzymes require non-protein components called cofactors for activity.
Cofactors can be inorganic ions (e.g., Mg²⁺, Zn²⁺) or organic molecules.
Organic cofactors can be coenzymes or prosthetic groups.
Coenzymes are small organic molecules, usually derived from vitamins (e.g., ATP, NAD, FAD).
Prosthetic groups are tightly bound, non-amino acid components (e.g., heme groups).
Cofactors can directly participate in the catalytic mechanism.

Enzyme Mechanisms: Lock and Key vs. Induced Fit

The lock-and-key model suggests that the enzyme's active site has a rigid shape that fits perfectly with the substrate.
The induced fit model proposes that the active site changes shape when the substrate binds. This change in shape precisely aligns the substrate for the reaction.

Factors Affecting Enzyme Activity

Temperature: Increasing temperature generally increases reaction rate up to a certain point. Exceeding the optimum temperature causes denaturation, reducing activity.
pH: Each enzyme has an optimal pH range where its activity is maximum. Extreme pH values can disrupt enzyme structure and decrease activity.
Substrate Concentration: Increasing substrate concentration increases the rate of reaction up to a point where the enzyme is saturated, and more substrate doesn't increase the rate.
Enzyme Concentration: Increasing enzyme concentration increases the reaction rate, as long as substrate is abundant.

Enzyme Inhibition

Competitive Inhibition: Inhibitors are similar in structure to the substrate, competing for binding at the active site. Increasing substrate concentration can overcome competitive inhibition.
Non-competitive Inhibition: Inhibitors bind to a site other than the active site, causing a change in the enzyme's shape that reduces activity. Increasing substrate concentration does not affect non-competitive inhibition.

Feedback Inhibition

Enzymes can be regulated by their product in a process called feedback inhibition. The product of a reaction inhibits an enzyme earlier in the pathway.

Enzyme Classification

Enzymes are classified into six major classes based on the types of reactions they catalyze.
Subclasses are based on the specific substrates acted upon.

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Description

Explore the fascinating world of enzymes, biological catalysts that accelerate biochemical reactions. This quiz delves into enzyme structures, the significance of the active site, and the role of substrates in enzymatic activity. Test your knowledge about the characteristics and functions of these essential proteins.