Changes in temperature or pH can cause enzymes to lose activity. What is a common feature of these two effects?
Temperature and pH affect the rate of substrate binding.
Temperature and pH both induce an enzyme to lose its precise three- dimensional shape.
Temperature and pH change the activation energy of the reaction.
Temperature and pH change the ionization state of cofactors.
There is no common mechanism of temperature and pH effects on enzyme activity.
The Correct Answer is B
A. Temperature and pH affect the rate of substrate binding:
Temperature and pH can influence binding rates indirectly, but this statement does not capture the primary shared mechanism by which extreme temperature or pH reduce enzyme activity.
B. Temperature and pH both induce an enzyme to lose its precise three-dimensional shape:
Both heat and extreme pH disrupt noncovalent interactions (hydrogen bonds, ionic bonds, hydrophobic interactions) that maintain tertiary and quaternary structure, causing loss of the active-site geometry and reduced catalytic activity.
C. Temperature and pH change the activation energy of the reaction:
Activation energy is an inherent property of a given catalyzed reaction; enzymes lower activation energy, but temperature and pH typically affect enzyme structure and kinetics rather than directly altering the chemical activation energy of the catalyzed step.
D. Temperature and pH change the ionization state of cofactors:
pH can change ionization states of cofactors and active-site residues; temperature less directly changes ionization state, so this does not represent a common mechanism for both.
E. There is no common mechanism of temperature and pH effects on enzyme activity:
There is a common mechanism: both can disrupt the weak bonds that maintain native protein structure, leading to loss of function.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. F+ cells: F+ cells contain the fertility (F) plasmid that encodes the genes required for pilus formation and DNA transfer during conjugation.
B. F− cells: F− cells lack the F plasmid and serve as recipients, not initiators, of conjugation.
C. All bacterial cells: Only cells possessing the F plasmid can initiate conjugation; therefore, not all bacterial cells are capable of this process.
Correct Answer is C
Explanation
A. Metabolism is the digestion of nutrients to release energy:
Digestion and energy release (catabolism) are parts of metabolism, but this statement omits the biosynthetic (anabolic) reactions that are also included.
B. Metabolism is the assembly of small molecules into macromolecules:
Assembly of small molecules (anabolism) is part of metabolism, but this statement excludes catabolic reactions that break down molecules.
C. Metabolism is all the chemical reactions of a cell (or organism), both anabolic and catabolic:
Metabolism encompasses both pathways that build molecules (anabolism) and pathways that break them down to release energy (catabolism), so this definition is comprehensive.
D. Metabolism is the production and expenditure of chemical energy:
Production and use of chemical energy are central aspects of metabolism but do not fully describe the wide variety of metabolic chemical transformations.
E. Metabolism is the assembly of macromolecules into cellular structures:
Assembly of macromolecules into structures (e.g., ribosomes, membranes) may occur, but metabolism more broadly includes many other chemical reactions beyond structural assembly.
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