Enzymes and Metabolic Reactions

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Questions and Answers

What term is used for the catalytically active form of an enzyme?

Cofactor

Substrate

Apoenzyme

Holoenzyme (correct)

Which factor does NOT affect enzyme activity?

Color of the solution (correct)

Substrate concentration

Temperature

Enzyme concentration

What is the optimum temperature range for enzymes in humans?

20-25 °C

35-40 °C (correct)

0-10 °C

70-75 °C

What term describes any substance that decreases the velocity of an enzyme-catalyzed reaction?

Inhibitor Signup and view all the answers

Which type of inhibition is characterized by the ability to be reversed?

Reversible inhibition Signup and view all the answers

What does Km reflect in enzyme kinetics?

Affinity for substrate Signup and view all the answers

Which of the following correctly describes the term 'activity' in enzymology?

The speed at which substrate converts to product Signup and view all the answers

What is the unit of enzyme activity defined as changing 1 µmol of substrate in 1 minute?

Unit Activity Signup and view all the answers

What is the primary function of enzymes in biochemical reactions?

To decrease the activation energy Signup and view all the answers

Which class of enzymes is responsible for the transfer of functional groups?

Transferases Signup and view all the answers

How do enzymes affect the speed of biochemical reactions?

They can increase the rate from 10^3 to 10^8 times faster. Signup and view all the answers

Which statement accurately describes enzyme specificity?

Enzymes have a specificity for their substrate and type of reaction. Signup and view all the answers

What are ribozymes?

Catalytic RNA molecules that serve as biocatalysts. Signup and view all the answers

Which of the following factors can affect enzyme activity?

Concentration of substrates and enzyme inhibitors Signup and view all the answers

In enzyme kinetics, what does the Michaelis-Menten constant (Km) represent?

The substrate concentration at which the reaction rate is half of Vmax Signup and view all the answers

Which type of enzyme inhibition decreases the reaction rate without permanently altering the enzyme?

Competitive inhibition Signup and view all the answers

Study Notes

Enzymes

Enzymes are biocatalysts, speeding up reactions by lowering activation energy.
They are not consumed in the reaction.
Enzymes are highly specific for their substrate and reaction.
Most enzymes are proteins, but ribozymes are catalytic RNA.
Enzymes change reaction rate (efficiency), not the reaction equilibrium.

Learning Objectives

Describe enzymes and their common properties
List the enzyme classifications correctly
Describe factors changing enzyme activity
Explain the relationship between Km and activity
Explain enzyme inhibition and types of inhibition

Metabolic Reactions

Enzymes catalyze metabolic reaction, speeding up anabolic and catabolic pathways.
Enzymes modify molecules, facilitate reactions, and aid in molecule transport.
Some reactions involve multiple steps with multiple enzymes.

Glycolysis

Glycolysis is a metabolic pathway where glucose is broken down to pyruvate.
Enzymes such as HK, PGI, PFK, ALDO, and others catalyze specific steps in this pathway

Activation Energy

Activation energy is the energy needed for a chemical reaction to start.
Enzymes lower the activation energy required for reactions to occur.
Enzymes speed up reactions by lowering the energy barriers and making them more favorable.

Activation Energy and Catalysts

Catalysts speed up reactions.
Catalysts lower the activation energy of reactions without being consumed in the process.
Enzymes are biological catalysts.

Enzymes (Biocatalysts)

Enzymes increase reaction rates.
Enzymes are biocatalysts that increase the reaction rate
Enzymes bind to substrates and make reactions faster.

Properties of Enzymes

Enzymes are proteins (except ribozymes).
They exhibit reaction specificity, meaning they only work on particular reactions.
They demonstrate substrate specificity (bind to a specific substrate).
Enzymes are highly efficient, increasing reaction rate up to millions of times faster.

Efficiency

Enzyme-catalyzed reactions occur much faster than non-catalyzed ones.
Carbonic anhydrase is exceptionally fast, hydrating CO2 molecules.

Specificity

Reaction specificity: A given enzyme catalyzes a specific reaction type.
Substrate specificity: A given enzyme uses a specific molecule or chemically related molecules.

Enzyme Nomenclature (Classification)

Enzymes are classified by EC numbers, a hierarchical system.
A classification system exists to differentiate enzymes by the specific reactions they catalyze.

Enzyme Kinetics and Km

Km represents enzyme affinity or how well an enzyme binds to its substrate.
A smaller Km signifies a higher affinity.
Vmax is the maximum reaction rate of an enzyme when saturated with substrate.

Km, A Clinical Example

Km values for alcohol dehydrogenase and aldehyde dehydrogenase vary depending on factors like the enzymes involved and the genes.
Lowering the Km of aldehyde dehydrogenase decreases the toxicity of acetaldehyde, relating to alcohol metabolism.

Regulation of Enzyme Activity

Enzyme activity is controlled by numerous processes.
Enzyme amount, modification, and location regulate enzyme activity.
Non-covalent and covalent modifications, and compartments regulate activity.

Regulation of Enzyme Activity (continued)

Phosphorylation/Dephosphorylation:
- Kinase activates the enzyme by adding a phosphate.
- Phosphatase deactivates the enzyme by removing the phosphate.
Feed-forward activation:
- A reaction activates a cascade of enzymes

Regulation of Enzyme Activity (Continued)

Feed-back inhibition:
- A reaction product inhibits an earlier enzyme step.
Compartmentalization:
- Enzymes are localized to specific cellular compartments.
Isozymes:
- Different forms of an enzyme with varying activities

Enzyme Structure (Active Site)

Apoenzyme: Protein portion of an enzyme.
Cofactor: Non-protein part of an enzyme (metal ion or coenzyme).
Holoenzyme: Complete enzyme with cofactor and apoenzyme.

Enzyme Activity

Activity (V) is the speed or rate at which an enzyme works.
Unit activity: enzyme activity that converts 1 µmol substrate in 1 minute under optimal conditions.

Factors Affecting Enzyme Activity

Enzyme concentration: increasing concentration means more reactions happen faster.
Substrate concentration: higher substrate leads to faster reaction initially, but only to a certain point.
Temperature: Enzymes operate best at particular temperatures.
pH: Optimal pH range varies based on enzymes and the environment.
Inhibitors: Molecules that reduce enzyme activity.

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Description

This quiz covers the properties and classifications of enzymes, their role in metabolic reactions, and specific pathways like glycolysis. Explore how enzymes function as biocatalysts and the factors influencing their activity. Test your understanding of enzyme inhibition and the relationship between Km and activity.