MODULE 6: Chapter 7.1 Flashcards
What is the most common type of heart disease?
Coronary heart disease
What contributes to the formation of plaques in coronary heart disease?
Deposits of cholesterol and other substances
What is the role of HMG-CoA reductase in cholesterol biosynthesis?
Catalyzes an early step in the cholesterol biosynthetic pathway
How does inhibition of HMG-CoA reductase affect cholesterol levels?
Lowers intracellular cholesterol levels by reducing its synthesis
What is the relationship between intracellular cholesterol and serum cholesterol uptake?
Lower intracellular cholesterol increases uptake from serum
What type of drugs were developed as a result of studies on HMG-CoA reductase?
Statin drugs
What is the primary function of enzymes in biological systems?
Accelerate the rates of chemical reactions
What distinguishes enzymes from other chemical catalysts?
Enzymes are not consumed in reactions and do not alter equilibrium concentrations
What are ribozymes?
Enzymes composed of RNA
What is the lock and key model of enzyme specificity?
Rigid physical and chemical complementarity between enzyme and substrate
What model did Daniel Koshland propose in 1958?
Induced-fit model of enzyme catalysis
In the induced-fit model, what does the enzyme represent?
A glove that accommodates a flexible substrate hand
What type of interactions occur between enzyme and substrate during binding?
Weak interactions such as hydrogen bonds and ionic interactions
What is bioavailability in the context of enzyme regulation?
Amount of enzyme present in the cell due to regulated gene expression
What are the two primary modes of enzyme regulation?
- Bioavailability
- Activity
What role does phosphorylation play in enzyme activity?
It is a common form of covalent modification that regulates activity
True or False: Enzymes can perform reactions without being affected by their environment.
False
What is the relationship between ΔG‡ and the rate constant k in enzyme kinetics?
They are related; changes in ΔG‡ affect the rate constant k
What does Michaelis–Menten kinetics describe?
The rate of enzyme-catalyzed reactions as a function of substrate concentration
What is the effect of enzyme regulation on cellular processes?
Maximizes energy balance between catabolic and anabolic pathways
What is the significance of enzyme active sites?
They are where substrates bind and reactions take place
Fill in the blank: Enzymes perform work in the cell by increasing the rates of ______.
Chemical reactions
What is the catalytic effect of enzymes on reaction rates?
They decrease the time it takes to reach equilibrium
What does the term ‘catalytic efficiency’ refer to in enzyme activity?
The effectiveness of an enzyme in catalyzing a reaction
What type of changes can occur in an enzyme upon substrate binding?
Structural changes in the enzyme
What are the key amino acid residues that orient substrates in enzyme active sites?
Examples include arginine
What is the role of NADPH in the mechanism of HMG-CoA reductase?
Serves as a cofactor
What is the result of the structural changes in hexokinase upon glucose binding?
Excludes water from the active site
What is the primary reason for enzyme regulation in cells?
To alter cell behavior in response to environmental stimuli
What is the equilibrium effect of catalysts on reactions?
Catalysts affect the rate of reactions without changing the final equilibrium or the overall change in free energy (ΔG).
What is the half-life (t1/2) of a reaction?
The time it takes for half of the reactant to decompose.
How can the half-life of the decomposition of hydrogen peroxide (H2O2) be decreased?
By adding a small amount of free iron (Fe2⁺/Fe3⁺) as a chemical catalyst.
What is the effect of catalase on the decomposition of H2O2?
Catalase increases the rate of decomposition by millions of molecules per second.
What is the order of magnitude of rate enhancement provided by catalase?
10^15-fold enhancement.
What theory explains how enzymes increase reaction rates?
Transition state theory.
What is the activation energy denoted as?
ΔG‡.
In the context of a reaction coordinate diagram, what does ΔG represent?
The change in free energy between the ground state of the reactant and the ground state of the product.
What is a holoenzyme?
An enzyme with a bound cofactor.
What happens when a cofactor is removed from an enzyme?
It produces an inactive apoenzyme.
List some common metal-ion cofactors found in enzymes.
- Fe2⁺
- Mg2⁺
- Mn2⁺
- Cu2⁺
- Zn2⁺
What role does Mg2⁺ play in enzymatic reactions?
Helps bind substrates or stabilize an intermediate or the transition state.
What is a coenzyme?
An enzyme cofactor with organic components.
What is a prosthetic group?
A coenzyme that is permanently associated with an enzyme.
What is the role of nicotinamide adenine dinucleotide (NAD⁺/NADH) in metabolism?
It acts as a coenzyme in many redox reactions involving dehydrogenase enzymes.
What is thiamine pyrophosphate (TPP) derived from?
Vitamin B1.
What is the consequence of thiamine pyrophosphate deficiency?
It results in the human disease beriberi, characterized by neurologic disorders.
What does lactate dehydrogenase do during anaerobic respiration?
It converts pyruvate to lactate.
What is the role of NADH in the lactate dehydrogenase reaction?
It functions as a transient electron carrier.
What must happen to NAD⁺ and NADH for another round of catalysis to occur?
They need to be regenerated to their original state.
What are NAD⁺ and NADH sometimes called?
Co-substrates
They are altered in the course of redox reactions through the donation or acceptance of electrons.
What is needed for NAD⁺ and NADH to participate in another round of catalysis?
They need to be regenerated to their original state via another reaction.
What is the oxidized form of lipoic acid called?
Lipoamide.
What is the reduced form of lipoamide?
Dihydrolipoamide.
What role does the dihydrolipoyl transacetylase enzyme play in the pyruvate dehydrogenase complex?
It performs the acyl transfer portion of the reaction.
How many enzymatic reactions are required for the metabolism of glucose to pyruvate in glycolysis?
10 enzymatic reactions.
What suffix do most proteins that function as enzymes end with?
-ase.
What is the common name for the enzyme that converts urea to ammonia and carbon dioxide?
Urease.
What does the term hexokinase refer to?
An enzyme that phosphorylates hexose sugars.
What classification system has been adopted by the International Union of Biochemistry and Molecular Biology (IUBMB) for enzymes?
A functional classification system based on six classes of enzymatic reactions.
What are the six classes of enzymatic reactions defined by the IUBMB?
- Oxidoreductase
- Transferase
- Hydrolase
- Lyase
- Isomerase
- Ligase.
What does the IUBMB classification number for hexokinase indicate?
EC 2.7.1.1, indicating it is a transferase that transfers a phosphoryl group.
How does glucokinase differ from hexokinase?
Glucokinase has a lower affinity for glucose and a more limited substrate specificity.
What is the significance of the IUBMB classification number?
It helps clear confusion associated with using historical or generic enzyme names.
What do enzymes do as biological catalysts?
They lower the activation energy (ΔG‡) of a reaction without affecting the overall change in free energy (ΔG).
What is the enzyme active site?
An optimal environment for chemical catalysis provided by enzymes.
What is bioavailability in the context of enzymes?
The amount of a nutrient or enzyme present in a cell that is capable of participating in a biochemical process.
What is a cofactor?
A small inorganic molecule that aids in the catalytic reaction mechanism within the enzyme active site.
What is a holoenzyme?
The assembled and catalytically active form of a multi-subunit enzyme or an enzyme that requires a cofactor.
What is an apoenzyme?
An enzyme without its cofactor.
What is a coenzyme?
An organic enzyme cofactor.
What is transition state theory?
The idea that the conversion of substrate to product involves a high-energy transition state.
What is activation energy (ΔG‡)?
The difference in energy between the ground state of a reactant and the transition state in a reaction.
