80 Questions
What is the approximate increase in the rate of a chemical reaction when catalyzed by an enzyme?
103-1020 x
What is the term for the energy required to reach the transition state from the ground state of the reactants?
Activation energy
What is the primary function of an enzyme's active site?
To bind to the substrate through noncovalent interactions
What is the name of the model that suggests the binding of the substrate induces a change in the conformation of the enzyme?
Induced fit model
What is the term for the unstable arrangement of atoms in which chemical bonds are in the process of being formed or broken?
Transition state
What percentage of enzymes are proteins?
99+%
What is the Vmax of an enzyme?
The maximum reaction rate reached when the enzyme is completely saturated with substrate
What does a low KM value indicate about an enzyme?
Small amount of substrate required for saturation
What is the unit of Kcat?
Seconds^-1
Why is it important to consider environmental effects on enzyme function?
Enzymes are sensitive to pH and temperature changes
What is the purpose of a Lineweaver-Burk plot?
To determine the Vmax and KM of an enzyme
What is the consequence of excessive heat on an enzyme?
Denaturation of the enzyme
What type of inhibition occurs when an inhibitor binds to the active site of an enzyme, competing with the substrate?
Competitive inhibition
What is the effect of an uncompetitive inhibitor on the Vmax and Km of an enzyme?
Vmax decreases, Km decreases
What type of inhibition is characterized by the formation of a covalent bond between the inhibitor and the enzyme?
Irreversible inhibition
What is the term for the phenomenon where the binding of one site on an enzyme affects the binding of other sites on the same molecule?
Cooperativity
What type of enzyme regulation involves the attachment and detachment of small chemical groups, such as phosphorylation and de-phosphorylation?
Reversible covalent modification
What is the term for an enzyme whose activity is affected by the binding of effectors, such as substrates, inhibitors, or activators?
Allosteric enzyme
What is the term for the process by which an effector molecule binds to an enzyme at a second site, changing the enzyme's activity?
Allosterism
What is the difference between a homotropic and a heterotropic allosteric modulator?
A homotropic modulator is a substrate, while a heterotropic modulator is not a substrate
What is the term for the phenomenon where the binding of one molecule to an enzyme increases the affinity for other molecules to bind?
Cooperativity
What is the term for the Greek word 'allo' meaning 'other' and 'steric' meaning 'shape'?
Allosteric
What is the type of allosteric regulation where an enzyme is inhibited by its own product?
Feedback inhibition
What is the term for an enzyme that can be regulated by both its substrates and other molecules?
Allosteric enzyme
What is the function of CTP synthetase enzyme?
To catalyze the ATP-dependent transfer of the amide nitrogen from glutamine to the C-4 position of UTP
What is the shape of the curve that describes the rate of ATCase catalysis vs substrate concentration?
Sigmoidal
What is the mechanism of feedback inhibition used by CTP?
Allosteric regulation
What is the main feature of the Concerted Model of allosterism?
All subunits change conformation simultaneously
What is the unique feature of the Sequential Model of allosterism?
Negative cooperativity
What is the difference between the Concerted and Sequential Models of allosterism?
The Concerted Model assumes all subunits are connected, while the Sequential Model assumes subunits are independent
Why does substrate-binding at one subunit only slightly alter the structure of other subunits?
To increase the substrate affinity in adjacent subunits
What is the result of phosphorylation on an inactive precursor enzyme?
It activates the enzyme
What is the function of a proenzyme?
It is an inactive precursor of an enzyme
What is the role of metal ions in enzymatic reactions?
They behave as cofactors
What is the purpose of NAD+ in redox reactions?
It is a two-electron oxidizing agent
What is the name of the process by which a proenzyme is converted to its active form?
Proteolysis
What is the result of substrate binding at one subunit?
It makes adjacent subunits more receptive to substrate
What is the name of the enzyme that is synthesized in the pancreas and stored in the small intestine?
Chymotrypsinogen
What is the purpose of a zymogen?
It is an inactive precursor of an enzyme
What is the name of the group that can form phosphate esters?
Hydroxyl groups
What is a characteristic of catalysts in chemical reactions?
They are not consumed during the reaction and increase the rate of the reaction
What is the primary purpose of the active site in an enzyme:
To bind the substrate and facilitate the catalytic reaction
Why is the induced fit model more likely to be the correct description of enzyme-substrate interaction?
Because the active site has a flexible shape that adapts to the substrate
What is the term for the energy required to reach the transition state?
Activation energy
What is the unique feature of enzymes compared to other biological molecules?
They have catalytic activity
What percentage of enzymes are proteins?
More than 99%
What is the effect of an allosteric inhibitor on the enzyme's activity?
It slows down the enzyme's activity.
What is the significance of KM in enzyme kinetics?
It is the dissociation constant for ES, indicating enzyme affinity for the substrate
What is the term for the binding of one molecule to an enzyme that increases the affinity for other molecules to bind?
Positive cooperativity
What is the purpose of enzyme kinetics?
All of the above
What is the term for an allosteric enzyme that can be regulated by both its substrates and other molecules?
Mixed allosteric enzyme
In which type of inhibition does the inhibitor bind to the active site of the enzyme, competing with the substrate?
Competitive inhibition
What is the effect of a high substrate concentration on enzyme activity?
It reaches the maximum reaction rate, Vmax
What is the term for the process by which an effector molecule binds to an enzyme at a second site, changing the enzyme's activity?
Allosteric regulation
What is the effect of a non-competitive inhibitor on the Vmax and Km of an enzyme?
Vmax decreases, Km remains the same
What is the role of an efficient enzyme?
It has a high turnover number and high affinity for the substrate
What is the significance of Vmax in enzyme kinetics?
It is the maximum reaction rate of an enzyme
What is the term for the Greek word 'allo' meaning 'other' and 'steric' meaning 'shape'?
Allosteric
What is the term for the phenomenon where the binding of one site on an enzyme affects the binding of other sites on the same molecule?
Cooperativity
What is the term for an allosteric modulator that is a substrate for its target enzyme?
Homotropic allosteric modulator
What is the type of enzyme regulation that involves the attachment and detachment of small chemical groups, such as phosphorylation and de-phosphorylation?
Reversible covalent modification
Why are enzyme kinetics important in pharmacology?
To develop inhibitors for specific enzymes, which can be used as drugs
What is the term for an enzyme whose activity is affected by the binding of effectors, such as substrates, inhibitors, or activators?
Allosteric enzyme
What is the result of an uncompetitive inhibitor binding to the Enzyme-Substrate (ES) complex?
Vmax decreases, Km remains the same
What is the function of CTP synthetase enzyme?
To catalyze the ATP-dependent transfer of the amide nitrogen from glutamine to the C-4 position of UTP to form CTP
What is the shape of the curve that describes the rate of ATCase catalysis vs substrate concentration?
Sigmoidal
What is the mechanism of feedback inhibition used by CTP?
Allosteric regulation
What is the main feature of the Concerted Model of allosterism?
Subunit are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits
What is the unique feature of the Sequential Model of allosterism?
Negative cooperativity, induced conformational changes that make the enzyme less likely to bind more molecules of the same type
What is the difference between the Concerted and Sequential Models of allosterism?
The Concerted Model involves all subunits changing conformation simultaneously, while the Sequential Model involves one subunit changing at a time
What is the result of substrate binding at one subunit?
The binding sites of other subunits are more receptive to substrate
What is the purpose of phosphorylation in enzyme regulation?
To activate or inactive the enzyme
What is a zymogen?
An inactive precursor of an enzyme
What is the role of metal ions in enzymatic reactions?
To act as cofactors
What is the term for the process by which a proenzyme is converted to its active form?
Proteolysis
What is the function of NAD+ in redox reactions?
To be a two-electron oxidizing agent
What is the result of phosphorylation on an inactive precursor enzyme?
The enzyme is converted to its active form
What is the purpose of a proenzyme?
To provide an inactive form of an enzyme that can be activated when needed
What is the group that can form phosphate esters?
Serine, threonine, and tyrosine
What is the term for the phenomenon where the binding of one site on an enzyme affects the binding of other sites on the same molecule?
Allosterism
Study Notes
Enzymes: Biological Molecules with Catalytic Activity
- 99+% of enzymes are proteins, but some RNA molecules are also catalytic
- Enzymes increase the rate of chemical reactions without being consumed
- Enzymes exhibit stereospecificity and function in physiological conditions
- Chemical reactions require energy input to reach the transition state, which is the unstable arrangement of atoms in the process of forming or breaking chemical bonds
Enzyme-Substrate Binding
- In an enzyme-catalyzed reaction, the substrate (S) binds to the active site of the enzyme through noncovalent interactions
- Binding models: lock-and-key model and induced fit model
- Induced fit model is the most likely mechanism, as it minimizes the distance to the transition state, allowing the enzyme to be an effective catalyst
Enzyme Kinetics
- Study of enzyme kinetics helps understand enzyme properties, such as substrate specificity, affinity, and mechanism of action
- Enzyme kinetic profile: Vmax (maximal reaction rate), Km (substrate concentration that gives ½ Vmax), and Lineweaver-Burk plot
- Km is a measure of enzyme affinity for the substrate
- Vmax is the maximum velocity of the reaction at saturating concentrations of substrate
Types of Enzyme Inhibition
- Reversible inhibitors: competitive, uncompetitive, and non-competitive (mixed)
- Competitive inhibition: inhibitor binds to the active site, increasing Km, and decreasing Vmax
- Uncompetitive inhibition: inhibitor binds to the ES complex, decreasing Vmax, and increasing Km
- Non-competitive (mixed) inhibition: inhibitor binds to both E and ES, decreasing Vmax, and increasing Km
- Irreversible inhibition: inhibitor forms a covalent bond with the enzyme, inactivating it
Environmental Effects on Enzyme Function
- Enzymes work best within a particular range of pH and temperature
- Extreme pH changes or excessive heat can denature the enzyme, destroying its catalytic ability
- Optimum pH and temperature vary depending on the enzyme and its environment
Allosteric Regulation
- Allosteric enzymes: activity is affected by the binding of effectors (substrate, inhibitor, or activator) to a site different from the active site
- Allosteric regulation: binding of effectors results in conformational changes in the enzyme, affecting its activity
- Cooperativity: trend that occurs when enzyme or protein contains multiple binding sites, where binding of one molecule increases or decreases the affinity for other molecules
- Homotropic and heterotropic allosteric regulation: substrate or regulatory molecule binds to the enzyme, affecting its activity
Models of Allosterism/Cooperativity
- Concerted model: the enzyme has only two conformations (R and T), and the binding of substrate shifts the equilibrium from the T to the R form
- Sequential model: subunits are not connected, and the binding of substrate induces a conformational change in the enzyme
Control of Enzyme Activity
- Phosphorylation: covalent modification of enzymes, adding or removing a phosphate group, which can activate or inactivate the enzyme
- Proenzymes: inactive precursors of enzymes, converted to the active form by proteolysis
- Zymogen: inactive precursor of an enzyme, converted to the active form by cleavage of one or more covalent bonds
- Coenzymes: nonprotein substances that take part in an enzymatic reaction and are regenerated for further reaction, such as metal ions, vitamins, and NAD+/NADH
Test your knowledge of enzymes, biological molecules that accelerate chemical reactions without being consumed. Learn about their structure, catalytic activity, and stereospecificity in physiological conditions.
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