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?

<p>Alanine racemase (C)</p> Signup and view all the answers

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

<p>Holoenzyme (B)</p> Signup and view all the answers

What defines the active site of an enzyme?

<p>The location where substrates bind and undergo reactions (C)</p> Signup and view all the answers

What are activators primarily responsible for in enzyme activity?

<p>Activating inactive enzymes (D)</p> Signup and view all the answers

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

<p>Chymotrypsin (B)</p> Signup and view all the answers

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

<p>The reaction rate increases linearly (A)</p> Signup and view all the answers

What role do cofactors play in enzyme activity?

<p>They assist the apoenzyme in catalyzing reactions (B)</p> Signup and view all the answers

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

<p>Optimal temperature (A)</p> Signup and view all the answers

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

<p>It leads to denaturation of the enzyme. (A)</p> Signup and view all the answers

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

<p>A rapid increase in reaction rate (A)</p> Signup and view all the answers

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

<p>To act as a catalyst that lowers the activation energy (A)</p> Signup and view all the answers

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

<p>Substrate temperature (D)</p> Signup and view all the answers

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

<p>The type of substrate that can fit and react (C)</p> Signup and view all the answers

What characterizes the optimal temperature for enzyme activity?

<p>It results in the most rapid reaction rate. (A)</p> Signup and view all the answers

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

<p>It does not explain the actual mechanism of reaction occurrence (B)</p> Signup and view all the answers

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

<p>Enzyme concentration is low compared to substrate concentration. (D)</p> Signup and view all the answers

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

<p>To stabilize the transition state during the reaction (B)</p> Signup and view all the answers

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

<p>The induced-fit model (C)</p> Signup and view all the answers

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

<p>By conducting kinetic studies and developing models (D)</p> Signup and view all the answers

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

<p>Enzymes can undergo conformational changes upon substrate binding (B)</p> Signup and view all the answers

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

<p>An intermediate enzyme-substrate complex (C)</p> Signup and view all the answers

What role do enzymes primarily serve in biochemical reactions?

<p>Act as biological catalysts (D)</p> Signup and view all the answers

What term describes an enzyme in its inactive form?

<p>Proenzyme (A)</p> Signup and view all the answers

Which statement about enzyme specificity is true?

<p>Enzymes exhibit stereospecificity for their substrates (B)</p> Signup and view all the answers

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

<p>Holoenzyme (C)</p> Signup and view all the answers

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

<p>Prosthetic group (D)</p> Signup and view all the answers

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

<p>A reaction may occur (C)</p> Signup and view all the answers

Which characteristic correctly distinguishes coenzymes from cofactors?

<p>Coenzymes are organic substances (C)</p> Signup and view all the answers

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

<p>To prevent premature activation (D)</p> Signup and view all the answers

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

<p>It becomes complementary to the substrate's shape. (A)</p> Signup and view all the answers

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

<p>It competes with the substrate for the active site. (C)</p> Signup and view all the answers

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

<p>Non-competitive inhibitor. (B)</p> Signup and view all the answers

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

<p>It will induce an increase in the rate of reaction. (B)</p> Signup and view all the answers

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

<p>Electric modification. (D)</p> Signup and view all the answers

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

<p>The enzyme is permanently inactivated. (B)</p> Signup and view all the answers

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

<p>It generally decreases the rate of reaction. (D)</p> Signup and view all the answers

What is the role of allosteric control in enzyme regulation?

<p>It modulates enzyme activity from a site distant from the active site. (D)</p> Signup and view all the answers

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

<p>It activates the enzyme by inducing a conformational change. (B)</p> Signup and view all the answers

What distinguishes isozymes from one another?

<p>They have slight structural differences. (D)</p> Signup and view all the answers

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

<p>They facilitate the reversible addition of phosphoryl groups. (D)</p> Signup and view all the answers

What characterizes proteolytic activation of an enzyme?

<p>It converts proenzymes into active forms via peptide bond hydrolysis. (C)</p> Signup and view all the answers

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

<p>Feedback inhibition (A)</p> Signup and view all the answers

What is the significance of enzymes in the human body?

<p>They are crucial for catalyzing nearly all chemical reactions necessary for life. (C)</p> Signup and view all the answers

What modification typically occurs during covalent modification of enzymes?

<p>A chemical group, often a phosphoryl group, is attached. (A)</p> Signup and view all the answers

Which factor can influence enzyme activity?

<p>Temperature and pH levels (C)</p> Signup and view all the answers

Flashcards

Enzymes

Biological catalysts that speed up chemical reactions without being consumed in the process.

Substrate

The molecule an enzyme acts upon.

Active Site

A region on the enzyme that binds the substrate.

Proenzyme or Zymogen

An inactive form of an enzyme that needs to be activated to function.

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Cofactor

A non-protein component that some enzymes require for activity.

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Coenzyme

An organic cofactor, often a vitamin derivative.

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Apoenzyme

An enzyme without its cofactor.

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Holoenzyme

An enzyme with its cofactor, ready to work.

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What is an activator?

A substance that increases the activity of an enzyme.

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What is inhibition?

A process that decreases the activity of an enzyme.

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What is an inhibitor?

A compound that inhibits or slows down the activity of an enzyme.

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What is enzyme activity?

A measure of the rate of a reaction that is catalyzed by an enzyme.

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How does enzyme concentration affect enzyme activity?

The increase in enzyme activity as the concentration of the enzyme increases.

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How does substrate concentration affect enzyme activity?

With a fixed enzyme concentration, increasing substrate concentration will initially increase reaction rate but eventually plateaus.

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How does temperature affect enzyme activity?

Enzymes have an optimal temperature where they function best. Above or below this temperature, activity decreases due to denaturation.

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How does pH affect enzyme activity?

Extreme pH levels can disrupt the enzyme's structure and affect its activity.

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Isomerase

A type of enzyme that catalyzes the rearrangement of atoms within a molecule, changing its structure but not its overall composition.

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Ligase

A type of enzyme that catalyzes the joining of two molecules by forming a new chemical bond, using energy from ATP.

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Proenzyme (Zymogen)

An inactive precursor of an enzyme. It must be activated by removing a small part of its polypeptide chain.

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Induced-Fit Model

This model explains how an enzyme changes shape to better accommodate the substrate. Think of it like a hand adjusting its grip on a ball.

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Enzyme Inhibitor

A molecule that slows down or stops an enzyme's activity. Imagine it as a jammed lock.

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Competitive Inhibition

This type of inhibition occurs when both the inhibitor and substrate compete for the same binding site on the enzyme.

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Non-competitive Inhibition

This type of inhibition happens when the inhibitor binds to a different site on the enzyme, changing the active site's shape and preventing the substrate from binding.

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Product Regulation

A type of regulation where the product of a reaction can control the enzyme's activity, like a thermostat regulating temperature.

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Allosteric Regulator

A molecule that can regulate an enzyme's activity by binding to a specific site, either activating or inhibiting it.

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Enzyme Specificity

Enzymes act specifically on their substrates, forming an intermediate complex called the enzyme-substrate complex which later decomposes to yield products and the free unchanged enzyme.

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Michaelis-Menten Model

Michaelis and Menten proposed a model describing how enzymes and substrates interact, with the enzyme reversibly binding to the substrate to form an intermediate complex.

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Enzyme-Substrate Complex

The enzyme-substrate complex is a temporary interaction between the enzyme and its specific substrate, essential for catalysis.

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Lock and Key Model

The Lock and Key model explains enzyme specificity, proposing that the active site of the enzyme has a specific shape complementary to the substrate.

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Product

The product is the final molecule resulting from the enzyme-catalyzed transformation of the substrate. It's the outcome of the enzyme's work.

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Isozymes or Isoenzymes

Different forms of the same enzyme with slightly different structures, leading to varying activity levels.

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Covalent Modification

Enzyme regulation where a chemical group, often a phosphate, is added or removed, altering the enzyme's activity.

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Proteolytic Activation

Regulation where an inactive form of an enzyme, a proenzyme or zymogen, is converted to its active form through irreversible cleavage.

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What are factors affecting enzyme activity?

Factors influencing enzyme activity. These could be temperature, pH, substrate concentration, enzyme concentration, and presence of inhibitors.

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What are the six basic enzyme types?

Six major categories of enzymes based on the types of reactions they catalyze: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.

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What are the two common types of enzyme inhibition?

Two common types of enzyme inhibition where a substance interferes with enzyme activity: competitive inhibition and non-competitive inhibition.

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What are four general types of enzyme regulation?

Four general types of enzyme regulation are allosteric, covalent modification, proteolytic activation, and multiple enzyme forms.

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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.

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