Question

1 how is a dna molecule arranged? a double - stranded with alternating deoxyribose and phosphate groups on the sides with adenine, guanine, cytosine, and thymine in the middle b double - stranded with alternating deoxyribose and phosphate groups on the sides with adenine, guanine, cytosine, and uracil in the middle c double - stranded with alternating ribose and phosphate groups on the sides with adenine, guanine, cytosine, and thymine in the middle d double - stranded with alternating ribose and phosphate groups on the sides with adenine, guanine, cytosine, and uracil in the middle

Explanation:

To determine the correct arrangement of a DNA molecule, we recall the structure of DNA:

• DNA is double - stranded.
• The backbone (sides) of the DNA molecule is made up of alternating deoxyribose (a sugar) and phosphate groups.
• The nitrogenous bases in the middle (rungs of the ladder - like structure) pair as adenine (A) with thymine (T) and guanine (G) with cytosine (C). Uracil (U) is a base found in RNA, not DNA, and ribose is the sugar in RNA, not DNA.
• Option A: It has the correct sugar (deoxyribose) in the backbone, the correct pairing of bases (adenine with thymine, guanine with cytosine) and the correct location of the backbone (sides) and bases (middle).
• Option B: DNA has deoxyribose, not ribose, and uracil is not in DNA, so B is incorrect.
• Option C: DNA has deoxyribose, not ribose, so C is incorrect.
• Option D: DNA has deoxyribose, not ribose, and uracil is not in DNA, so D is incorrect.

Answer:

A. double - stranded with alternating deoxyribose and phosphate groups on the sides with adenine, guanine, cytosine, and thymine in the middle