Enzymes and Their Properties

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Questions and Answers

Which statement accurately describes the role of enzymes in biochemical reactions?

Enzymes are completely consumed during the reactions they catalyze.

Enzymes only work in the digestive system.

Enzymes accelerate biochemical reactions without being changed themselves. (correct)

Enzymes change their structure after catalyzing a reaction.

What are isozymes?

Enzymes that are catalyzed by the same substrate.

Enzymes that differ in amino acid sequence but catalyze the same reaction. (correct)

Enzymes that are non-proteins acting as catalysts.

Enzymes that are produced only in the digestive tract.

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

To regulate the temperature at which reactions occur.

To bind the substrate and facilitate the reaction. (correct)

To store the product of reactions.

To change the enzyme's structure after binding the substrate.

Which of the following factors can affect enzyme activity?

Temperature and pH levels Signup and view all the answers

What is the significance of the 'lock-and-key' model in enzymatic reactions?

It illustrates the specificity of enzymes for their substrates. Signup and view all the answers

In the context of lactate dehydrogenase, what does the presence of different isozymes indicate?

They exhibit variation in tissue distribution and properties. Signup and view all the answers

What does the binding of a substrate to an enzyme result in?

A change in the enzyme's conformation to form a stable complex. Signup and view all the answers

Which class of enzymes is involved in the transfer of functional groups?

Transferases Signup and view all the answers

Which statement correctly describes coenzymes?

They are organic molecules often derived from vitamins. Signup and view all the answers

What characteristic primarily determines an enzyme's specificity for its substrate?

The three-dimensional arrangement of amino acids in the enzyme. Signup and view all the answers

What term describes an enzyme that lacks its coenzyme?

Apoenzyme Signup and view all the answers

What is the energy barrier that must be overcome for a reaction to proceed called?

Activation energy Signup and view all the answers

How does an increase in ΔG affect reaction velocity?

It decreases the reaction velocity. Signup and view all the answers

Which factor would likely affect enzyme activity by changing the environment of the enzyme?

Temperature of the reaction Signup and view all the answers

In what way does lemon juice prevent the browning of sliced apples?

By changing the pH of the enzyme environment to inhibit activity. Signup and view all the answers

Which of the following best describes the maximum rate of an enzyme-catalyzed reaction?

It is reached when all active sites of the enzyme are saturated. Signup and view all the answers

What happens to the rate of an enzyme-catalyzed reaction as substrate concentration increases?

The rate increases until it reaches Vmax. Signup and view all the answers

At what condition is an enzyme considered to be operating at maximum activity?

At steady state. Signup and view all the answers

How does temperature affect the velocity of an enzymatic reaction?

Velocity increases to a peak before decreasing with higher temperatures. Signup and view all the answers

What is the relationship between pH and enzyme activity?

pH affects the ionization of active site groups and can lead to denaturation. Signup and view all the answers

What represents the maximum reaction velocity in Michaelis-Menten kinetics?

The plateau phase of the velocity curve. Signup and view all the answers

What is KM in the context of Michaelis-Menten kinetics?

The substrate concentration at which reaction velocity equals 50% of Vmax. Signup and view all the answers

What occurs when an enzyme becomes saturated with substrate?

The enzyme activity plateaus and cannot increase further. Signup and view all the answers

What effect can extreme temperatures have on enzyme activity?

They can lead to temperature-induced denaturation of the enzyme. Signup and view all the answers

Study Notes

Enzymes

Enzymes are biologically active proteins that speed up the breakdown of food.
Enzymes are biological catalysts; they accelerate reactions without being consumed or altered.
Enzymes are involved in crucial life processes, including DNA replication, transcription, protein synthesis, metabolism, and signal transduction.

Enzyme Classification and Properties

The provided document lists topics to be learned including classification of enzymes, their properties, holoenzymes, apoenzymes, cofactors, coenzymes, mechanisms of enzyme action, kinetics of chemical reactions, and factors affecting enzyme activity (substrate concentration, pH, temperature).
These topics, along with enzyme classes (Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases) are part of a comprehensive study of enzymes.

Active Site

Enzyme molecules have an active site, a pocket or cleft where substrates bind.
The active site's shape is crucial for substrate recognition.
Active sites contain amino acid residues that participate in substrate binding and catalysis.
Substrate binding to the enzyme forms an enzyme-substrate complex.

Substrate-Binding Sites

Enzyme specificity, the ability of an enzyme to react with a particular substrate, arises from the precise 3D arrangement of amino acids in the active site.
The "lock-and-key" and "induced-fit" models describe how substrates bind to enzymes.

Enzyme-Substrate Models

Enzymes can be flexible.
After substrate binding, the enzyme's structure changes to create a stable enzyme-substrate complex.
The binding site of the enzyme is rigid, accommodating only substrates of the correct shape.

Cofactors and Coenzymes

Many enzymes require cofactors (non-protein helper molecules) for optimal activity.
Cofactors can be temporary (bound by ionic or hydrogen bonds) or permanent (bound by covalent bonds).
Coenzymes are a subset of cofactors. They are organic molecules often derived from vitamins.
Enzymes with bound coenzymes are termed holoenzymes, while enzymes without are apoenzymes.

Factors Affecting Enzyme Reaction Velocity

Substrate Concentration: Reaction velocity increases with substrate concentration until the enzyme becomes saturated.
Temperature: Reaction velocity increases with temperature until a peak, then decreases due to enzyme denaturation.
pH: The concentration of protons ([H+]) affects reaction velocity. Extreme pH values can lead to enzyme denaturation.

Isoenzymes

Isoenzymes are enzymes that catalyze the same reaction but differ in amino acid sequence.
Tissues contain specific isoenzymes or combinations.
Isozyme levels in the blood can indicate tissue damage (e.g., heart attack)

Michaelis-Menten kinetics

Vmax is the maximum reaction velocity.
Km is the Michaelis constant, reflecting the affinity of the enzyme for its substrate.
A small Km indicates high affinity, while a large Km indicates low affinity.

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Description

This quiz covers essential concepts about enzymes, including their classification, properties, and the role of active sites in catalyzing biological reactions. It provides insight into various enzyme classes and crucial factors that affect enzyme activity. Test your understanding of enzyme dynamics and functions in biological processes.