Biochemistry: Enzymes and Oxidoreductases

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Questions and Answers

What is the primary role of an enzyme?

To transport molecules across membranes

To break down nutrients into waste products

To speed up biochemical reactions (correct)

To store energy for cellular functions

Which type of enzyme is composed solely of protein?

Conjugated enzyme

Hydrolase

Transferase

Simple enzyme (correct)

What is a cofactor in the context of conjugated enzymes?

An enzyme that catalyzes oxidation-reduction

The protein part of an enzyme

A type of hydrolase enzyme

A nonprotein part required for activity (correct)

Which enzyme class catalyzes the transfer of a functional group from one molecule to another?

Transferase Signup and view all the answers

What characterizes a holoenzyme?

It is the active form of a conjugated enzyme Signup and view all the answers

What type of reaction is catalyzed by a hydrolase?

Addition of a water molecule to break a bond Signup and view all the answers

Which enzyme class is responsible for removing a group to form a double bond?

Lyase Signup and view all the answers

What does the enzyme-substrate complex represent?

An intermediate formed during enzyme activity Signup and view all the answers

What is the primary function of an isomerase enzyme?

To catalyze the isomerization of a substrate. Signup and view all the answers

Which statement best describes the induced-fit model of enzyme action?

The active site can change shape to better accommodate the substrate. Signup and view all the answers

What is meant by enzyme specificity?

An enzyme's activity is restricted to a specific substrate or type of reaction. Signup and view all the answers

What is enzyme activity a measure of?

The rate at which substrates convert to products Signup and view all the answers

What does an enzyme inhibitor do?

Slows or stops the normal catalytic function of an enzyme Signup and view all the answers

How does a ligase enzyme function?

By connecting two molecules into one using ATP. Signup and view all the answers

Why is the geometry of a substrate important for enzyme action?

It ensures the substrate can fit into the active site. Signup and view all the answers

What temperature is considered optimal for human enzymes?

37°C Signup and view all the answers

How does pH affect enzyme activity?

It influences the charge of amino acids at the active site Signup and view all the answers

What role does ATP play in the function of ligase enzymes?

ATP supplies the energy necessary for bonding two molecules. Signup and view all the answers

What does reversible competitive inhibition involve?

Binding of an inhibitor to the active site Signup and view all the answers

Which characteristic is NOT associated with enzyme specificity?

Allows for catalysis of multiple unrelated substrates. Signup and view all the answers

An enzyme's active site is most similar to what mechanism?

A specific lock that only fits a certain key. Signup and view all the answers

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

It leads to a saturation curve Signup and view all the answers

What is the optimal pH for pepsin to function effectively?

2.0 Signup and view all the answers

What characterizes irreversible noncompetitive inhibition?

It binds to an enzyme site other than the active site Signup and view all the answers

What characterizes uncompetitive inhibitors in the context of enzyme activity?

They form strong covalent bonds to a specific amino acid at the active site. Signup and view all the answers

How does phosphorylation influence enzyme activity?

It serves as a switch to activate or deactivate the enzyme. Signup and view all the answers

In the context of allosteric enzymes, what is a positive regulator's role?

It changes the shape of the active site to enhance substrate binding. Signup and view all the answers

Which statement best describes the process of covalent modification of enzymes?

It permanently alters the enzyme structure through chemical group modification. Signup and view all the answers

What is the primary effect of dephosphorylation on an enzyme?

It removes phosphate groups, potentially altering enzyme activity. Signup and view all the answers

In feedback control mechanisms for enzyme activity, what triggers the regulation?

The product of the reaction sequence. Signup and view all the answers

Which of these statements about protein kinases is correct?

They are involved in the addition of phosphate groups to enzymes. Signup and view all the answers

What distinguishes allosteric enzymes from typical enzymes?

They have multiple protein chains and regulatory sites. Signup and view all the answers

Which type of enzyme specificity is exhibited by catalase?

Absolute specificity Signup and view all the answers

Which enzyme is an example of group specificity?

Carboxypeptidase Signup and view all the answers

What type of specificity allows an enzyme to act on a specific type of chemical bond?

Linkage specificity Signup and view all the answers

Which enzyme does not catalyze the D-form of amino acids?

L-amino acid oxidase Signup and view all the answers

Which type of enzyme specificity is considered the most general?

Linkage specificity Signup and view all the answers

Which of the following statements regarding enzyme concentrations is accurate?

Enzymes do not require a high concentration relative to substrates. Signup and view all the answers

What type of specificity refers to the enzyme's action on molecules with a particular functional group?

Group specificity Signup and view all the answers

Hydrogen peroxide is the substrate for which enzyme with absolute specificity?

Catalase Signup and view all the answers

Study Notes

General Properties of Oxidoreductases

Catalyze oxidation–reduction reactions.
Enzymes are typically proteins that accelerate biochemical reactions.

Types of Enzymes

Simple Enzyme: Composed solely of protein.
Conjugated Enzyme: Contains both protein (apoenzyme) and nonprotein (cofactor) components. A holoenzyme is the functional conjugated enzyme.
Transferase: Transfers functional groups between molecules, with subtypes including transaminases and kinases.
Hydrolase: Catalyzes hydrolysis reactions, breaking bonds through the addition of water.
Lyase: Facilitates the addition or removal of groups to/from double bonds without hydrolysis.
Isomerase: Catalyzes the rearrangement of substrate atoms into isomers.
Ligase: Joins two molecules with the involvement of ATP.

Models of Enzyme Action

Enzyme-Substrate Complex: Intermediate formed when a substrate binds to the enzyme's active site.
Lock-and-Key Model: The active site has a fixed shape, fitting only substrates with complementary geometry.
Induced-Fit Model: Enzyme's active site adapts to better fit the incoming substrate, allowing for shape changes.

Enzyme Specificity

Refers to the enzyme's restriction to specific substrates, reactions, or bonds.
Absolute Specificity: Enzyme catalyzes only one reaction (e.g., catalase for hydrogen peroxide).
Group Specificity: Acts on substrates with specific functional groups (e.g., carboxypeptidase operates on carboxyl end of peptides).
Linkage Specificity: Acts on specific chemical bonds (e.g., phosphatases targeting phosphate-ester bonds).
Stereochemical Specificity: Acts on specific stereoisomers (e.g., L-amino acid oxidase for L-form amino acids).

Factors Affecting Enzyme Activity

Temperature: Increased temperature raises kinetic energy, affecting reaction rates. Human enzymes peak at 37°C.
pH: Enzyme activity is influenced by the surrounding pH; optimal pH varies by enzyme (e.g., pepsin at pH 2, trypsin at pH 8).
Substrate Concentration: Increased substrate concentration enhances activity until saturation, forming a saturation curve.

Enzyme Inhibition

Enzyme Inhibitor: Slows or halts enzyme function by binding to it.
Reversible Competitive Inhibition: Inhibitor competes with substrate for active site.
Reversible Noncompetitive Inhibition: Inhibitor attaches to an alternative site, reducing enzyme activity.
Covalent Modification: Alters enzyme activity through covalent attachment or removal of chemical groups.

Regulation of Enzyme Activity

Allosteric Enzymes: Contain multiple protein chains, with regulatory binding sites that influence activity. Positive regulators enhance activity.
Feedback Control: Regulates the first reaction in a sequence via the product of that pathway.
Phosphorylation: Addition of phosphate groups acts as an on/off switch for enzyme activity.
Dephosphorylation: Removal of phosphate groups, affecting enzyme activity inversely.

Protein Kinases

Enzymes that facilitate the addition of phosphate groups, playing a crucial role in enzyme regulation.

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Description

Explore the world of enzymes with a focus on oxidoreductases and their general properties. This quiz will test your knowledge of enzyme structures and classifications, including simple enzymes and transferases. Perfect for biochemistry students looking to reinforce their understanding of enzyme-catalyzed reactions.