Enzymes Overview Quiz

Enzymes

• Enzymes are biocatalysts, speeding up biochemical reactions.
• They are proteins (most cases) or ribozymes (RNA).
• Enzymes lower activation energy, making reactions proceed faster.
• They are not consumed in reactions.
• Enzymes have specificity for reactions and substrates.
• Enzyme activity depends on factors like concentration, temperature, pH, inhibitors, and cofactors.
• Enzymes are composed of an apoenzyme and a cofactor or coenzyme.
• The combination of the apoenzyme and cofactor forms a holoenzyme.
• The active site of an enzyme interacts with the substrate.
• Reaction velocity is a measure of enzyme activity.
• Optimal temperature and pH levels are optimal for enzyme function.
• Enzyme inhibitors can decrease reaction velocity.
• Enzyme kinetics describe how enzymes interact with substrates, and Km is a measure of enzyme affinity.
• Enzyme regulation includes changes in enzyme amount or modification, and compartmentalization.
• Isozymes are different forms of the same enzyme, with different structures and functions.
• Isozymes can be seen in different areas of the body.

Learning Objectives

• Students will be able to describe enzymes and their properties.
• Students will be able to list the classifications of enzymes.
• Students will be able to explain factors affecting enzyme activity.
• Students will be able to expalin the relationship between Km and enzyme activity.
• Students will be able to describe and explain enzyme inhibition.

Metabolic Reactions

• Enzymes facilitate both anabolic and catabolic reactions.
• Enzymes speed up reactions by lowering activation energy.
• Classic biochemical reaction has an enzyme that speeds it up.
• Enzymes can modify or transport substrate molecules.
• With some specific molecules, enzymes aid in different processes.

Glycolysis

• Glycolysis is a series of enzymatic reactions converting glucose into pyruvate.
• Several enzymes are involved, each catalyzing a specific step.

Activation Energy

• Activation energy is the energy required for a reaction to start.
• Enzymes lower the activation energy, thus making it easier for the reaction to start.
• Enzymes are not consumed during the reaction process.
• Activation energy is the minimal amount of needed energy for the reaction to start.

Activation Energy and Catalysts

• Catalysts, including enzymes, increase the reaction rate.
• Catalysts do not change the reaction or reaction equilibrium.
• Catalysts lower activation energy, making reactions happen faster.
• Catalysts remain unchanged at the end of the reaction.

Enzymes (Page 8)

• Enzymes are biocatalysts that speed up reactions.
• Substrates bind to the active site.
• Enzymes increase the reaction rate for substrate to product conversion.

Properties of Enzymes

• Most enzymes are proteins.
• Ribozymes are catalytic RNAs.
• Enzymes change the reaction rate.
• Enzymes have specificity for substrates and the reaction.
• Enzymes cause the amount of reaction to increase, but don't change the equilibrium.

Efficiency

• Enzyme-catalyzed reactions are significantly faster than uncatalyzed reactions.
• Carbonic anhydrase is a highly efficient enzyme.

Specificity

• Reaction specificity describes the type of reaction an enzyme catalyzes.
• Substrate specificity describes the specific types of molecules enzymes use.

Enzyme Nomenclature: Classification

• Enzymes are classified according to their function and the types of reactions they catalyze.
• An enzyme is listed based on its function. This determines the classification of the enzyme.

ExploreNZ - The Enzyme Database (Page 13)

• This database organizes enzymes by class, subclass, and sub-subclass.
• Allows users to search and find information on enzymes.
• Provides complete classification tree.

Enzyme Structure

• Apoenzyme = protein part
• Cofactor = non-protein part
• Holoenzyme = catalytically active form
• Active site = the location of the substrate binding and reaction.

Enzyme Structure: Active Site

• Active site is composed of many amino acids.
• Amino acids in active site bind to the substrates.

Enzyme Activity

• Enzyme activity is measured in units like U/min or µmol/min.
• Activity is a measure of speed.
• Enzyme activity converts the substrate into product in a certain time.

Factors Affecting Enzyme Activity

• Enzyme and substrate concentration affect reaction rate.
• Temperature affects enzyme structure and function.
• pH affects enzyme structure and function.
• Inhibitors affect enzyme function.
• Ionic bonds and denaturation change shape of enzyme.

Enzyme Concentration

• Increasing enzyme concentration increases reaction rate to products.
• Increase in enzyme and substrate concentrations increases reaction velocity and product amount.

Substrate Concentration

• Increasing substrate concentration increases reaction rate until the active sites become saturated.

Temperature

• Increasing temperature generally increases reaction rate but above a certain point, it may decrease activity due to denaturation.
• Optimum temperature is best for enzyme function. Different enzymes have different optimum temps.

pH

• Enzymes have an optimal pH range.
• Different enzymes have different optimal pH values; they vary in their activity levels and change according to the change in pH.
• Optimum pH changes activity of enzymes.

Inhibitors

• Inhibitors decrease enzyme activity.
• Inhibitors are substances that decrease reaction velocity.
• Inhibitors can be reversible or irreversible.
• Different types of inhibitors impact the enzyme in different ways.

Reversible Inhibition

• Competitive inhibitors compete with the substrate for the active site.
• Noncompetitive inhibitors bind to the enzyme at a site other than the active site.
• Uncompetitive inhibitors bind to the enzyme-substrate complex, decreasing the reaction rate.
• All types of reversible inhibitors decrease enzyme activity.

Enzyme Kinetics and Km

• Km is a measure of enzyme affinity for its substrate.
• Affinitive describes the substrate-enzyme bond.
• High Km values indicate low affinity and vice-versa.
• Vmax represents the maximum velocity or speed of an enzyme-catalyzed reaction.

Km, A Clinical Example

• Km values can be clinically important and are used to measure the toxicity of the substrate.
• Km can be used to measure the toxicity of certain substrates.

Regulation of Enzyme Activity

• Enzyme activity can be regulated by changing enzyme amount (synthesis and degradation).
• Enzyme activity can be regulated by covalent and non-covalent modifications.
• Enzyme location, or compartmentalization, affects activity.
• Different forms of the same enzyme can exist (isozymes).
• Factors including regulation by covalent modifications, protein interactions, and feed-forward and feedback inhibition.