Enzymes: Functions, Types, and Characteristics

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Questions and Answers

What is the main function of cofactors in enzyme activity?

To cleave bonds by adding water

To activate proenzymes

To increase the activation energy of a reaction

To help apoenzymes become holoenzymes (correct)

Where are extracellular enzymes found?

In the gastrointestinal tract, blood, and extracellular matrix (correct)

In the nucleus of cells

Only in the extracellular matrix

In the cytoplasm of cells

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

To bind the substrate and lower the activation energy (correct)

To increase the activation energy of a reaction

To cleave bonds by adding water

To transfer electrons between molecules

What type of enzymes transfer electrons between molecules?

Oxidoreductases Signup and view all the answers

What is the purpose of compartmentalizing enzymes into organelles within cells?

To separate specific biochemical pathways Signup and view all the answers

What type of enzymes break chemical bonds without hydrolysis or oxidation-reduction?

Lyases Signup and view all the answers

What is the function of acetylcholinesterase, a plasma membrane enzyme?

To degrade extracellular neurotransmitters Signup and view all the answers

What is the shape of the reaction velocity curve with increasing substrate concentration?

Hyperbolic Signup and view all the answers

Which of the following is NOT a characteristic of enzymes?

They are consumed during reactions. Signup and view all the answers

Isoenzymes differ from regular enzymes in that they:

Are encoded by different genes, resulting in slight structural variations. Signup and view all the answers

Which of the following statements is TRUE about proenzymes?

They are inactive forms of enzymes that are activated by proteolytic cleavage. Signup and view all the answers

How do cofactors assist enzymes in catalyzing reactions?

They bind to the active site and directly participate in the reaction. Signup and view all the answers

Why are enzymes compartmentalized within cells?

All of the above. Signup and view all the answers

Which of the following is NOT a function of extracellular enzymes?

Regulating gene expression. Signup and view all the answers

What type of enzyme inhibitors bind to the active site of an enzyme and compete with the substrate for binding?

Competitive inhibitors. Signup and view all the answers

Which of the following is NOT a mechanism of enzyme activity regulation?

Competitive inhibition. Signup and view all the answers

Study Notes

Characteristics of Enzymes

Enzymes are catalysts that are not consumed in reactions
They are mainly proteins, highly specific, and interact with substrates

Isoenzymes

Isoenzymes are different enzymes that catalyze the same reaction but are produced by different tissues
Example: hexokinase/glucokinase

Proenzymes

Proenzymes (or zymogens) are inactive enzymes with extra protein sequences
They are activated by cutting off the extra protein sequence
Mainly found as extracellular enzymes, e.g. digestive proteases

Cofactors

Cofactors help apoenzymes become holoenzymes
Types of cofactors:
- Metal ions that can bind substrates
- Small organic molecules (coenzymes) derived from vitamins
Cofactors participate in oxidation and reduction reactions

Enzyme Compartmentalization

Enzymes are found intracellularly, compartmentalized into their organelles
This separates specific biochemical pathways

Extracellular Enzymes

Found in:
- Gastrointestinal tract (to digest dietary macromolecules)
- Blood (to mediate blood clot formation)
- Extracellular matrix (for remodeling during normal tissue turnover and tissue injury)

Plasma Membrane Enzymes

Sit inside the cell membrane
Examples:
- Acetylcholinesterase degrades extracellular neurotransmitters
- Cyclooxygenases produce inflammatory mediators

Enzyme Catalysis

The active site allows for catalytic activity due to its cofactors and amino acid side chains that bind the substrate
Enzymes lower activation energy, and the binding of substrate to enzyme further lowers activation energy to make the reaction easier

Classes of Enzymes

1. Oxidoreductases: transfer electrons between molecules
1. Transferases: transfer functional groups
1. Hydrolases: cleave bonds by adding water
1. Lyases: break chemical bonds (not by hydrolysis or oxidation-reduction)
1. Isomerases: rearrange molecule structure
1. Ligases: form bonds between two large molecules

Enzyme Kinetics

Reaction velocity shows saturation kinetics with increasing substrate concentration (hyperbolic curve)

Allosteric Enzymes

Allosteric enzymes differ from regular enzymes in their regulation

Environmental Factors Affecting Enzyme Function

Various environmental factors affect enzyme function

Michaelis-Menten Kinetics

Vmax and Km represent the maximum reaction rate and the substrate concentration at which the reaction rate is half of Vmax, respectively

Lineweaver Burk Plot

Provides information about substrate binding affinity and maximum reaction rate

Enzyme Inhibitors

Irreversible enzyme inhibitors: covalently bind to enzymes, permanently inactivating them
Reversible enzyme inhibitors: bind non-covalently to enzymes, reducing their activity
Examples of competitive inhibitors: succinate and malonate
Noncompetitive inhibitors affect enzyme kinetics differently than competitive inhibitors

Mechanisms of Enzyme Activity Regulation

Proenzymes typically activated by cutting off extra protein sequences
Allosteric effectors influence enzyme activity
Feedback inhibition regulates enzyme activity
Phosphorylation and dephosphorylation regulate enzyme activity

Diagnostics

Creatine Phosphokinase is used in diagnosing heart attacks
Enzyme levels change during tissue or organ damage
Different tissues produce different versions of enzymes that catalyze the same reaction

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Description

This quiz covers the key characteristics of enzymes, types of enzymes, and their functions in the cell. It also explores how enzymes catalyze reactions, cofactors, and more.