RNA molecules differ from DNA molecules because only RNA
does not have thymine.
has uracil.
All of the choices are correct.
is typically one strand of nucleotides (single stranded)
has ribose.
The Correct Answer is C
A. does not have thymine: DNA contains the nitrogenous base thymine, whereas RNA lacks thymine. Instead, RNA uses uracil in place of thymine during base pairing. Because thymine is absent from RNA molecules, this difference is one of the key biochemical distinctions between RNA and DNA structure.
B. has uracil: RNA contains the nitrogenous base uracil, which pairs with adenine during RNA synthesis and function. In DNA, thymine performs this role instead. The substitution of uracil for thymine is a defining molecular feature that distinguishes RNA nucleotides from DNA nucleotides.
C. All of the choices are correct: Each of the listed statements accurately describes a property unique to RNA compared with DNA. RNA lacks thymine, contains uracil, typically exists as a single-stranded molecule, and contains ribose sugar rather than deoxyribose. Because every option describes a valid structural difference, this is the most accurate answer.
D. is typically one strand of nucleotides (single stranded): RNA molecules are generally single-stranded, allowing them to fold into complex secondary and tertiary structures that support functions such as translation and gene regulation. DNA, in contrast, usually exists as a double-stranded helix with complementary base pairing between strands.
E. has ribose: RNA nucleotides contain ribose sugar, which includes a hydroxyl group on the 2′ carbon of the pentose ring. DNA contains deoxyribose, which lacks this oxygen atom. This chemical difference contributes to RNA being more reactive and less stable than DNA.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. Guanine: Guanine pairs with cytosine in both DNA and RNA through three hydrogen bonds. It does not pair with uracil, as the chemical structure of uracil does not allow stable hydrogen bonding with guanine.
B. Adenine: In RNA, uracil replaces thymine and forms two hydrogen bonds with adenine. This base-pairing maintains the complementary structure needed for RNA transcription and folding, ensuring accurate coding during protein synthesis.
C. Thymine: Thymine is found only in DNA and pairs with adenine. In RNA, uracil substitutes for thymine, so thymine does not pair with uracil.
D. Cytosine: Cytosine pairs with guanine via three hydrogen bonds in both DNA and RNA. Cytosine does not pair with uracil because the hydrogen bonding does not match the structural requirements.
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.
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