Each nucleotide is composed of
one phosphate, one nitrogenous base, one sugar.
one phosphate, one nitrogenous base, two sugars.
two phosphates, one nitrogenous base, two sugars.
one phosphate, two nitrogenous bases, one sugar.
The Correct Answer is A
A. one phosphate, one nitrogenous base, one sugar: A nucleotide, the basic building block of nucleic acids, consists of a phosphate group, a five-carbon sugar (deoxyribose in DNA or ribose in RNA), and a single nitrogenous base (adenine, thymine, cytosine, guanine, or uracil in RNA). The phosphate forms the backbone of the nucleic acid chain, the sugar provides structural support, and the base carries the genetic information.
B. one phosphate, one nitrogenous base, two sugars: Nucleotides contain only one sugar, not two. Including two sugars would create a structure inconsistent with the polymerization and base-pairing rules of nucleic acids.
C. two phosphates, one nitrogenous base, two sugars: This composition is incorrect because a nucleotide contains one phosphate and one sugar. Two phosphates are only present in nucleoside diphosphates (like ADP), which are energy carriers, not in standard nucleotides forming DNA or RNA strands.
D. one phosphate, two nitrogenous bases, one sugar: Each nucleotide contains only one nitrogenous base. Having two bases would disrupt proper base pairing and the linear structure required for DNA and RNA strands.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Thick peptidoglycan layer: Gram-positive bacteria have a thick, multilayered peptidoglycan cell wall that retains the crystal violet-iodine complex during the Gram staining process. This dense layer prevents the dye from being washed out during the alcohol decolorization step, causing Gram-positive bacteria to appear purple under a microscope.
B. Outer membrane: The outer membrane is characteristic of Gram-negative bacteria, not Gram-positive bacteria. It contains lipopolysaccharides and provides an additional barrier but does not contribute to the retention of crystal violet in Gram-positive organisms.
C. Lipopolysaccharide: Lipopolysaccharides (LPS) are components of the outer membrane of Gram-negative bacteria and play a role in pathogenicity and immune activation. LPS is absent in Gram-positive bacteria and therefore does not influence their purple coloration during Gram staining.
Correct Answer is D
Explanation
A. an extremophile: Extremophiles are organisms that thrive in extreme environmental conditions, such as very high or very low pH, salinity, or pressure. While thermophiles can be considered a type of extremophile, the term extremophile is broader and does not specifically describe organisms adapted primarily to high temperatures.
B. thermoduric: Thermoduric organisms are those that can survive short exposures to high temperatures but do not necessarily grow optimally at those temperatures. They are often heat-resistant spores or bacteria that survive pasteurization, rather than thriving at 45–60°C.
C. a facultative psychrophile: Facultative psychrophiles are organisms capable of growing at low temperatures but can tolerate higher temperatures. Their optimal growth range is typically below 20°C, making this classification inconsistent with a 45–60°C growth range.
D. a thermophile: Thermophiles are microorganisms that grow optimally at elevated temperatures, typically between 45°C and 80°C. They possess enzymes and cellular structures adapted to resist denaturation at high temperatures, which allows them to thrive in environments such as hot springs, compost piles, or industrial processes.
E. a psychrophile: Psychrophiles are cold-loving organisms that grow optimally at temperatures below 15°C and are adapted to Arctic, Antarctic, or deep-sea habitats. A growth range of 45–60°C is far beyond their tolerance, making this classification incorrect.
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