60 Questions
What is the role of enzymes in chemical reactions?
Enzymes act as biological catalysts, increasing reaction rates by lowering activation barriers.
What happens in the absence of enzyme catalysis in chemical reactions?
Chemical reactions could not occur on a useful time scale, hindering the sustenance of life.
What is the consequence of excessive activity of an enzyme?
It can lead to disease.
Why are measurements of enzyme activities in blood plasma, erythrocytes, or tissue samples important?
They are important in diagnosis.
What is a key characteristic of enzyme catalysis?
Enzymes exhibit a very high degree of specificity.
Which statement best describes the transition state in a reaction?
It is the point at which decay to substrate or product are equally likely.
What is the relationship between equilibrium constant (K′eq) and standard free-energy change (∆G′°)?
∆G′° = −RT ln K′eq
What does the activation energy (∆G‡) represent in a reaction?
The difference between the ground state energy level and the transition state energy level.
How do catalysts affect reaction rates and equilibria?
Catalysts lower the activation energy and increase the reaction rate, but do not affect the equilibrium point.
What is the role of the enzyme-substrate complex in enzyme-catalyzed reactions?
It is central to the action of enzymes.
Which mechanism by which the enzyme itself undergoes a conformational change when the substrate binds, induced by multiple weak interactions with the substrate?
Induced fit
What is the measure of the affinity an enzyme has for its substrate, as the lower the value of Km, the more efficient the enzyme is at carrying out its function at a lower substrate concentration?
Km (Michaelis constant)
What type of catalysis occurs when a transient covalent bond forms between the enzyme and the substrate?
Covalent catalysis
What serves to bring specific functional groups on the enzyme into the proper position to catalyze the reaction?
Induced fit
What is the discipline focused on determining the rate of a reaction and how it changes in response to changes in experimental parameters?
Enzyme kinetics
What is the Michaelis-Menten equation for a one-substrate enzyme-catalyzed reaction?
$V0 = Vmax\frac{[S]}{Km + [S]}$
What does a Lineweaver-Burk plot reveal for competitive inhibition?
Lines intersect at the y-axis
What happens to the apparent Km in the presence of an uncompetitive inhibitor?
Increases
What is the relationship between V0, Vmax, [S], and Km in the Michaelis-Menten equation?
$V0 = Vmax\frac{[S]}{Km + [S]}$
What is the equation for the dissociation constant, Kd, for reactions with two steps?
$k2 + k^{-1}Km = k1$
What is the rate equation for a second-order reaction involving compounds S and T?
$V = k[ST]$
What type of interactions mediate the interactions between enzymes and substrates?
Ionic interactions and the hydrophobic effect
What is the range in which enzymes enhance rates of reactions?
5 to 17 orders of magnitude
What type of interactions between enzyme and substrate lower the activation energy?
Covalent interactions
What overcomes barriers to reaction such as the entropy of molecules in solution and substrate distortion?
Binding energy
What serves as transient carriers of specific atoms or functional groups in enzymatic reactions?
Coenzymes such as biotin, coenzyme A, flavin adenine dinucleotide, lipoate, and others
What are enzymes classified into based on the type of reaction they catalyze?
Seven classes with subclasses
What is the primary factor on which the catalytic activity of enzymes depends?
The integrity of the native protein conformation
What was the name given to the molecules detected in cell-free yeast extracts that could ferment sugar to alcohol?
Enzymes
What do enzyme active sites use to lower the activation barrier of catalyzed reactions?
Binding energy
What is the rate equation for a first-order reaction?
$V = k[S]$
What type of interactions between enzyme and substrate lower the activation energy?
Covalent interactions
What is the relationship between rate constant k and activation energy ∆G‡?
Inverse and exponential
What do enzymes enhance rates in the range of?
5 to 17 orders of magnitude
What type of reaction depends on the concentration of two different compounds?
Second-order reaction
What is the primary factor on which the catalytic activity of enzymes depends?
Substrate concentration
What serves as transient carriers of specific atoms or functional groups in enzymatic reactions?
Coenzymes
What are enzymes classified into based on the type of reaction they catalyze?
Seven classes
What do enzyme active sites use to lower the activation barrier of catalyzed reactions?
Binding energy
What is the measure of the affinity an enzyme has for its substrate, as the lower the value of $K_m$, the more efficient the enzyme is at carrying out its function at a lower substrate concentration?
$K_m$
What is the consequence of excessive activity of an enzyme?
Increased risk of disease
What serves as practical tools in chemical engineering, food technology, and agriculture?
Enzymes
What is the primary factor on which the catalytic activity of enzymes depends?
Substrate concentration
What is the role of enzymes in chemical reactions?
Catalyze reactions
What are the fundamental conditions for life according to the text?
Self replication and chemical reactions catalyzed by enzymes
What is the relationship between the transition state and the ground state in a reaction?
The transition state is the point at which decay to substrate or product are equally likely, while the ground state is the starting point for the reaction
What is the activation energy (∆G‡) in a reaction?
The difference between the ground state energy level and the transition state energy level
What do catalysts do to affect reaction rates and equilibria?
Lower the activation energy and increase the reaction rate without affecting the equilibrium point
What is the relationship between equilibrium constant (K′eq) and standard free-energy change (∆G′°)?
∆G′° = −RT ln K′eq
What is the biochemical standard free-energy change, ∆G′°, at pH 7.0?
∆G′° = the standard free energy change at pH 7.0
What is the Michaelis constant, Km, a measure of?
The affinity an enzyme has for its substrate
What is the primary function of induced fit in enzyme catalysis?
To bring specific functional groups on the enzyme into the proper position to catalyze the reaction
What type of catalysis occurs when a transient covalent bond forms between the enzyme and the substrate?
Covalent catalysis
What does the maximum rate of the reaction, Vmax, represent?
The maximum rate of the reaction when all the enzyme’s active sites are saturated with substrate
What is the role of metal ions in enzyme catalysis?
To mediate oxidation-reduction reactions by reversible changes in the metal ion’s oxidation state
What is the relationship between substrate concentration and initial reaction rate, as expressed by the Michaelis-Menten equation?
$V_0 = \frac{V_{max}[S]}{K_m + [S]}$
What type of plot yields a straight line for enzymes obeying the Michaelis-Menten relationship?
Lineweaver-Burk plot of 1/V0 versus 1/[S]
What happens to the apparent $K_m$ in the presence of an uncompetitive inhibitor?
Increases by the factor α
What is the equation for the Lineweaver-Burk plot?
$\frac{1}{V_0} = \frac{1}{V_{max}} + \frac{1}{K_m[S]}$
What does a Lineweaver-Burk plot reveal for competitive inhibition?
Lines intersect at the y axis
Study Notes
Enzymes: Key Principles and Characteristics
- Enzymatic reactions occur in specialized pockets called active sites where the conversion of a substrate to a product takes place.
- Enzymes bind most tightly to the transition state of the catalyzed reaction, using binding energy to lower the activation barrier.
- Enzyme active sites are organized by evolution to facilitate multiple mechanisms of chemical catalysis simultaneously.
- Many enzymes are regulated through reversible covalent modification, binding of allosteric modulators, proteolytic activation, noncovalent binding to regulatory proteins, and elaborate regulatory cascades.
- Biological catalysis was first recognized in the late 1700s, and the name "enzymes" was given to the molecules detected in cell-free yeast extracts that could ferment sugar to alcohol.
- Most enzymes are proteins, and their catalytic activity depends on the integrity of the native protein conformation.
- Enzymes have a wide range of molecular weights, from 12,000 to over 1 million, and may require additional chemical components such as cofactors and coenzymes.
- Inorganic ions such as Cu2+, Fe2+/Fe3+, K+, Mg2+, Mn2+, Mo, Ni2+, and Zn2+ serve as cofactors for various enzymes.
- Coenzymes such as biotin, coenzyme A, flavin adenine dinucleotide, lipoate, and others serve as transient carriers of specific atoms or functional groups.
- Enzymes may contain prosthetic groups, and the complete catalytically active enzyme together with its bound coenzyme and/or metal ions is known as a holoenzyme.
- Enzymes are classified into seven classes based on the type of reaction catalyzed, each with subclasses, and most enzymes have trivial names in addition to their systematic and enzyme commission numbers.
- Each enzyme has a four-part enzyme commission number (E.C. Number) and a systematic name that classifies them based on the type of reaction they catalyze.
Enzymes: Key Principles and Characteristics
- Enzymatic reactions occur in specialized pockets called active sites where the conversion of a substrate to a product takes place.
- Enzymes bind most tightly to the transition state of the catalyzed reaction, using binding energy to lower the activation barrier.
- Enzyme active sites are organized by evolution to facilitate multiple mechanisms of chemical catalysis simultaneously.
- Many enzymes are regulated through reversible covalent modification, binding of allosteric modulators, proteolytic activation, noncovalent binding to regulatory proteins, and elaborate regulatory cascades.
- Biological catalysis was first recognized in the late 1700s, and the name "enzymes" was given to the molecules detected in cell-free yeast extracts that could ferment sugar to alcohol.
- Most enzymes are proteins, and their catalytic activity depends on the integrity of the native protein conformation.
- Enzymes have a wide range of molecular weights, from 12,000 to over 1 million, and may require additional chemical components such as cofactors and coenzymes.
- Inorganic ions such as Cu2+, Fe2+/Fe3+, K+, Mg2+, Mn2+, Mo, Ni2+, and Zn2+ serve as cofactors for various enzymes.
- Coenzymes such as biotin, coenzyme A, flavin adenine dinucleotide, lipoate, and others serve as transient carriers of specific atoms or functional groups.
- Enzymes may contain prosthetic groups, and the complete catalytically active enzyme together with its bound coenzyme and/or metal ions is known as a holoenzyme.
- Enzymes are classified into seven classes based on the type of reaction catalyzed, each with subclasses, and most enzymes have trivial names in addition to their systematic and enzyme commission numbers.
- Each enzyme has a four-part enzyme commission number (E.C. Number) and a systematic name that classifies them based on the type of reaction they catalyze.
Test your knowledge of enzymes with this quiz on the key principles and characteristics of enzymatic reactions. Explore topics such as enzyme classification, active sites, cofactors, coenzymes, and regulatory mechanisms. Brush up on your understanding of biological catalysis and learn about the diverse range of enzymes and their molecular weights.
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