Enzyme Overview and Classification

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Questions and Answers

What type of enzyme catalyzes the joining of two molecules using energy from ATP?

Isomerases

Ligases (correct)

Hydrolases

Oxidoreductases

What is the term for the inactive form of an enzyme?

Apoenzyme

Zymogen (correct)

Cofactor

Holoprotein

Which component is essential for the function of an apoenzyme?

Prosthetic group

Product

Cofactor (correct)

Substrate

Which enzyme converts L-alanine to D-alanine?

Alanine racemase Signup and view all the answers

What is the complete enzyme consisting of the apoenzyme, its cofactor, and coenzyme called?

Holoenzyme Signup and view all the answers

What defines the active site of an enzyme?

The location where substrates bind and undergo reactions Signup and view all the answers

What are activators primarily responsible for in enzyme activity?

Activating inactive enzymes Signup and view all the answers

Which of the following is an example of a simple enzyme?

Chymotrypsin Signup and view all the answers

What effect does increasing enzyme concentration have on reaction rate, assuming substrate concentration is constant?

The reaction rate increases linearly Signup and view all the answers

What role do cofactors play in enzyme activity?

They assist the apoenzyme in catalyzing reactions Signup and view all the answers

Which factor has a sharp decreasing effect on enzyme activity when surpassed?

Optimal temperature Signup and view all the answers

What happens to enzyme activity when the pH is extremely high or low?

It leads to denaturation of the enzyme. Signup and view all the answers

What is the effect of increasing substrate concentration on enzyme activity at first?

A rapid increase in reaction rate Signup and view all the answers

What is the primary function of an enzyme in a biochemical reaction?

To act as a catalyst that lowers the activation energy Signup and view all the answers

Which factor does NOT affect the catalytic process of enzyme activity?

Substrate temperature Signup and view all the answers

According to the lock-and-key model, what does the shape of the enzyme dictate?

The type of substrate that can fit and react Signup and view all the answers

What characterizes the optimal temperature for enzyme activity?

It results in the most rapid reaction rate. Signup and view all the answers

What is a limitation of the lock-and-key model?

It does not explain the actual mechanism of reaction occurrence Signup and view all the answers

How does enzyme concentration typically relate to substrate concentration in a cell?

Enzyme concentration is low compared to substrate concentration. Signup and view all the answers

What is the role of the enzyme-substrate complex in enzymatic reactions?

To stabilize the transition state during the reaction Signup and view all the answers

Which model overcomes the limitations of the lock-and-key model?

The induced-fit model Signup and view all the answers

How did Michaelis and Menten contribute to the understanding of enzyme reactions?

By conducting kinetic studies and developing models Signup and view all the answers

What does the induced-fit model suggest about enzyme activity?

Enzymes can undergo conformational changes upon substrate binding Signup and view all the answers

What is formed when an enzyme combines with a substrate during the enzymatic reaction process?

An intermediate enzyme-substrate complex Signup and view all the answers

What role do enzymes primarily serve in biochemical reactions?

Act as biological catalysts Signup and view all the answers

What term describes an enzyme in its inactive form?

Proenzyme Signup and view all the answers

Which statement about enzyme specificity is true?

Enzymes exhibit stereospecificity for their substrates Signup and view all the answers

What is the term for the combination of an apoenzyme and its cofactor?

Holoenzyme Signup and view all the answers

Which of the following is an example of a tightly bound coenzyme?

Prosthetic group Signup and view all the answers

What happens when a substrate binds to the active site of an enzyme?

A reaction may occur Signup and view all the answers

Which characteristic correctly distinguishes coenzymes from cofactors?

Coenzymes are organic substances Signup and view all the answers

What is the main purpose of producing enzymes in an inactive form?

To prevent premature activation Signup and view all the answers

What occurs to the active site of an enzyme in the induced-fit model after the substrate binds?

It becomes complementary to the substrate's shape. Signup and view all the answers

What is the primary action of a competitive inhibitor in enzyme inhibition?

It competes with the substrate for the active site. Signup and view all the answers

Which type of enzyme inhibitor alters the active site without directly competing for it?

Non-competitive inhibitor. Signup and view all the answers

What effect does an increase in substrate concentration generally have on enzyme activity if unregulated?

It will induce an increase in the rate of reaction. Signup and view all the answers

Which mechanism is NOT one of the four general types of enzyme regulation?

Electric modification. Signup and view all the answers

What is the outcome when an enzyme's active site is irreversibly altered by a compound?

The enzyme is permanently inactivated. Signup and view all the answers

In feedback control, how does an increase in product concentration generally affect enzyme activity?

It generally decreases the rate of reaction. Signup and view all the answers

What is the role of allosteric control in enzyme regulation?

It modulates enzyme activity from a site distant from the active site. Signup and view all the answers

What is the role of a regulator in an allosterically regulated enzyme?

It activates the enzyme by inducing a conformational change. Signup and view all the answers

What distinguishes isozymes from one another?

They have slight structural differences. Signup and view all the answers

What is the primary function of protein kinases in enzyme regulation?

They facilitate the reversible addition of phosphoryl groups. Signup and view all the answers

What characterizes proteolytic activation of an enzyme?

It converts proenzymes into active forms via peptide bond hydrolysis. Signup and view all the answers

Which of the following is NOT a type of enzyme regulation mentioned?

Feedback inhibition Signup and view all the answers

What is the significance of enzymes in the human body?

They are crucial for catalyzing nearly all chemical reactions necessary for life. Signup and view all the answers

What modification typically occurs during covalent modification of enzymes?

A chemical group, often a phosphoryl group, is attached. Signup and view all the answers

Which factor can influence enzyme activity?

Temperature and pH levels Signup and view all the answers

Study Notes

Enzyme Overview

Enzymes are biological molecules, primarily proteins, acting as catalysts
They speed up reactions without being consumed
Highly specific, often targeting only one substrate
Include stereospecificity, the 3D arrangement of atoms in the substrate
Can exist entirely of protein or with cofactors (metal ions or organic substances)
Apoenzyme: enzyme lacking cofactor
Holoenzyme: combination of apoenzyme and cofactor
Metalloenzyme: apoenzyme + metal ion cofactor
Prosthetic group: tightly bound coenzyme

Enzyme Classification

Classified by the Enzyme Commission (EC) of the International Union of Biochemistry
Numerical system: EC number with four numbers, separating decimal points
Major class is the first number
Group the enzyme transfers is the second number
Destination the transferred group the third number
Refinement of third number is the last number
Six basic types based on the reaction type they catalyze

Six Basic Types of Enzymes

Oxidoreductases: catalyze redox reactions (electron transfer)
Transferases: transfer functional groups
Hydrolases: catalyze hydrolysis reactions (using water to break bonds)
Lyases: catalyze addition to or removal of groups from double bonds
Isomerases: catalyze isomerization reactions
Ligases: catalyze linking of two molecules with ATP hydrolysis

Enzyme Structure

Some enzymes are simple polypeptides (e.g., chymotrypsin, pepsin)
Others are conjugated proteins with non-protein prosthetic groups (cofactors)
Apoenzyme: protein portion of enzyme
Cofactor: non-protein part of enzyme (inorganic or organic e.g., metal ion, coenzyme)
Holoenzyme: complete enzyme (apoenzyme + cofactor)
Active site: region on enzyme where substrate binds
Substrate: molecule that enzyme acts on

Enzyme Inhibition

Competitive inhibition: inhibitor competes with substrate for active site
Non-competitive inhibition: inhibitor binds to another site, altering enzyme shape
Enzyme inhibition can be reversible (inhibitor detaches) or irreversible (inactivates permanently)

Factors Affecting Enzyme Activity

Enzyme concentration: higher concentration, faster reaction rate
Substrate concentration: rapid increase then leveling-off
Temperature: optimal temp, higher rates, higher temp, enzyme denatures
pH: optimal range, affects enzyme's ionic state, extreme values denature

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Description

Explore the fascinating world of enzymes, biological catalysts crucial for speeding up biochemical reactions. Learn about their structure, types, and classification, including the Enzyme Commission's numerical system for identifying various enzymes. This quiz will enhance your understanding of enzyme mechanisms and their specific roles in biological processes.