At temperatures higher than the maximum growth temperature for an organism,
proteins are permanently denatured.
membranes become too fluid for proper function.
hydrogen bonds within molecules are broken.
hydrogen bonds are broken and proteins are permanently denatured.
hydrogen bonds are broken, proteins are denatured, and membranes become too fluid.
The Correct Answer is E
A. Proteins are permanently denatured: Heat can denature proteins by disrupting noncovalent interactions; however, saying “permanently” is too absolute — some proteins may refold if conditions return to normal.
B. Membranes become too fluid for proper function: Elevated temperatures increase membrane fluidity (phospholipid tails become more disordered), impairing membrane integrity and function. This is true but incomplete alone.
C. Hydrogen bonds within molecules are broken: High temperature disrupts hydrogen bonds (and other weak interactions) that stabilize protein secondary/tertiary structure and nucleic acids; again this is true but incomplete by itself.
D. Hydrogen bonds are broken and proteins are permanently denatured: This combines two effects (bond disruption and denaturation). It’s closer, but “permanently” may be incorrect in some cases where refolding is possible — and it still omits membrane effects.
E. Hydrogen bonds are broken, proteins are denatured, and membranes become too fluid: High temperatures disrupt hydrogen bonding, cause protein denaturation, and increase membrane fluidity, all of which together explain why growth stops above the maximum growth temperature.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. True: Ionizing radiation (gamma rays, X-rays) penetrates deeply and causes ionizations that break DNA and other critical molecules, making it generally more effective at inactivating microbes and spores than nonionizing UV, which has more limited penetration.
Correct Answer is E
Explanation
A. In mitochondria:
Mitochondria are intracellular organelles in eukaryotes where many metabolic reactions occur, but exoenzymes are secreted enzymes that act outside the cell rather than inside organelles.
B. Within the cell membrane:
Some enzymes are membrane-associated and act at or through the membrane, yet exoenzymes are secreted beyond the cell surface to act on extracellular substrates.
C. In lysosomes:
Lysosomes contain hydrolytic enzymes that function inside the cell to digest materials; exoenzymes operate outside the cell rather than within intracellular digestive organelles.
D. In cytoplasm:
Cytoplasmic enzymes catalyze intracellular reactions; exoenzymes are exported and function extracellularly.
E. Outside of the cell:
Exoenzymes are secreted by the cell into the external environment (or into host tissues) where they break down large molecules into smaller units the cell can transport or where they contribute to pathogenicity.
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