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Questions and Answers

What is the primary function of enzyme catalysts in a chemical reaction?

Bind products and convert them to substrates

Bind substrates and prevent the reaction from occurring

Bind and rearrange products into reactants

Bind reactants, convert them to products, and release the products (correct)

How do isoenzymes differ from each other?

They catalyze different reactions and have the same amino acid sequence

They catalyze the same reaction and have the same amino acid sequence

They catalyze different reactions but have the same amino acid sequence

They catalyze the same reaction but have a different amino acid sequence (correct)

How are enzymes typically named?

By adding the prefix -ose to their catalyzed reaction

By adding the suffix –ase to the name of their substrate or catalyzed reaction (correct)

By the molecular weight of their products

By the color of the substrate they catalyze

In which enzyme classification do oxidation-reduction reactions take place?

Oxidoreductases Signup and view all the answers

What do hydrolases catalyze in a chemical reaction?

Cleavage of bonds by the addition of water Signup and view all the answers

Which property is true for virtually all enzymes?

They are proteins Signup and view all the answers

What type of reactions do ligases catalyze?

Formation of bonds between C and O, S, or N at the expense of ATP Signup and view all the answers

What happens to enzymes during their participation in a chemical reaction sequence?

They may be modified but eventually return to their original form Signup and view all the answers

Which group of enzymes catalyze the transfer of C-, N- or P-containing groups?

Transferases Signup and view all the answers

What is the key factor that determines an enzyme’s name?

The type of reaction it catalyzes Signup and view all the answers

What is the function of coenzymes in enzyme-catalyzed reactions?

Act as temporary carriers of groups in reactions Signup and view all the answers

Which type of enzymes do not follow Michaelis-Menten kinetics?

Allosteric enzymes Signup and view all the answers

What is the role of the active site in enzyme-catalyzed reactions?

Stabilizes the formation of the high energy transition state Signup and view all the answers

What is the Michaelis constant (Km) in enzyme kinetics?

The substrate concentration that gives half the maximal rate (Vmax) Signup and view all the answers

Why do enzymes increase the rate of a reaction?

By lowering the activation energy needed for the reaction Signup and view all the answers

Which hypothesis states that the binding of a substrate results in changes in the shape of the enzyme to enhance binding?

Induced Fit Hypothesis Signup and view all the answers

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

Increases until a maximal velocity (Vmax) is reached Signup and view all the answers

Which option describes allosteric enzymes?

'Sigmoidal curve' displaying enzymes Signup and view all the answers

'ES complex' refers to:

'Enzyme-Substrate' intermediate complex formed during reactions Signup and view all the answers

'Lineweaver-Burk Equation' is primarily used for:

'Graphical representation' of Michaelis-Menten kinetics Signup and view all the answers

What is the effect of increasing enzyme concentration on the rate of a reaction?

The rate of the reaction will increase proportionally. Signup and view all the answers

What is the optimal temperature range for most human enzymes?

35-40C Signup and view all the answers

What is the effect of increasing temperature beyond the optimal range on enzyme activity?

The reaction velocity decreases due to enzyme denaturation. Signup and view all the answers

What is the international unit of enzyme activity?

1 mol of product formed per minute Signup and view all the answers

What is the effect of pH extremes on enzyme activity?

pH extremes can lead to denaturation of the enzyme. Signup and view all the answers

How does a competitive inhibitor affect enzyme activity?

It affects Km but not Vmax. Signup and view all the answers

How does a non-competitive inhibitor affect enzyme activity?

It affects Vmax but not Km. Signup and view all the answers

What is the purpose of measuring enzyme activity in blood, erythrocytes, or tissue samples?

To diagnose certain illnesses. Signup and view all the answers

What is the key difference between irreversible and reversible enzyme inhibitors?

Irreversible inhibitors bind covalently, while reversible inhibitors bind non-covalently. Signup and view all the answers

How can the effect of a competitive inhibitor be overcome?

By increasing the substrate concentration. Signup and view all the answers

Study Notes

Enzyme Characteristics

Enzymes are biological molecules, mostly proteins, that catalyze chemical reactions
They are highly specific, interacting with one or a few substrates and catalyzing one type of reaction
Enzymes increase the rate of a reaction by factors of 1 million or more, but do not affect the equilibrium of a reaction
They remain unchanged after the reaction has occurred, providing a place for the reaction to occur

Enzyme Nomenclature

Enzymes are named based on the type of reaction they catalyze
The suffix –ase is usually added to the name of the substrate or reaction they catalyze
Examples: Lactase (hydrolyzes lactose into glucose and galactose), DNA polymerase (polymerizes deoxynucleotides to form DNA)

Classification of Enzymes

Enzymes can be grouped into six main classes:
- Oxidoreductases (oxidation-reduction reactions)
- Transferases (transfer of C-, N-, or P-containing groups)
- Hydrolases (catalyze cleavage of bonds by the addition of water)
- Lyases (addition or removal of groups to form double bonds)
- Isomerases (transfer of groups within molecules to form isomers)
- Ligases (formation of bonds between C and O, S, or N at the expense of ATP)

Properties of Enzymes

Virtually all enzymes are proteins
Some enzymes require cofactors (inorganic ions like Fe2+, Mn2+) or coenzymes (organic compounds like NAD, CoA) to catalyze reactions
Prosthetic groups are cofactors or coenzymes tightly or covalently linked to the enzyme protein

Mechanism of Enzyme-Catalyzed Reactions

Enzyme-catalyzed reactions involve the formation of a complex between the substrate and enzyme (ES complex)
The active site of an enzyme is the place where the reaction occurs
Substrate binding to the active site increases the local concentration of reactants and stabilizes the formation of the high-energy transition state
Enzymes work by lowering the activation energy needed for a reaction to occur

Michaelis-Menten Model

Describes how the reaction velocity (V0) varies with substrate concentration ([S])
The Michaelis-Menten equation can be rearranged to give a linear plot (Lineweaver-Burk equation)
Km (Michaelis constant) is the substrate concentration that gives half the maximal rate (Vmax)
Low Km means high affinity of the enzyme to the substrate, while high Km means low affinity

Effect of Enzyme Concentration

The rate of a reaction is directly proportional to the concentration of enzyme
Doubling the amount of enzyme doubles the amount of product produced per minute

Effect of Temperature

The reaction velocity increases with temperature until a peak velocity is reached
Further elevation of the temperature results in a decrease in reaction velocity due to temperature-induced denaturation of the enzyme
The optimum temperature for most human enzymes is between 35 and 40°C

Effect of pH

The catalytic process usually requires specific chemical groups in either an ionized or unionized state
Extreme pH values can lead to denaturation of the enzyme

Inhibition of Enzyme Activity

Two types of enzyme inhibition: irreversible and reversible
Irreversible inhibitors bind covalently to the enzyme molecule to destroy enzyme function
Reversible inhibitors bind non-covalently to the enzyme, with two types:
- Competitive inhibitors (e.g., allopurinol, statins) compete with the substrate for binding at the active site
- Non-competitive inhibitors (allosteric regulation) bind to a site other than the active site, affecting Vmax but not Km

International Unit of Enzyme Activity

1 unit of enzyme activity is defined as the amount of enzyme causing transformation of 1.0 micromol of substrate per minute under optimal conditions of measurement

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Description

Explore the role of enzymes in catalyzing chemical reactions and the concept of isoenzymes. Learn how enzymes bind substrates, convert them into products, and return to their original form. Understand the efficiency and selectivity of enzyme catalysts.