Question

question:
the outer part of dna is composed of

answer options:
select one of four
rna.
a ribose and phosphate backbone.
nucleotides.
a deoxyribose and phosphate backbone.

Explanation:

To determine the correct answer, we analyze the structure of DNA. DNA (deoxyribonucleic acid) has a double - helix structure. The outer part (the backbone) of the DNA strand is made up of alternating deoxyribose (a sugar) and phosphate groups.

• Option "RNA" is incorrect because DNA and RNA are different nucleic acids, and the outer part of DNA is not composed of RNA.
• Option "a ribose and phosphate backbone" is incorrect. Ribose is the sugar in RNA, while DNA has deoxyribose.
• Option "nucleotides" is incorrect. Nucleotides are the building blocks of DNA, and each nucleotide consists of a sugar, a phosphate, and a nitrogenous base. The outer part (backbone) is made of the sugar - phosphate part, not the entire nucleotide.
• Option "a deoxyribose and phosphate backbone" is correct as it accurately describes the composition of the outer (backbone) part of the DNA molecule.

Answer:

D. a deoxyribose and phosphate backbone. (assuming the options are labeled A: RNA, B: a ribose and phosphate backbone, C: nucleotides, D: a deoxyribose and phosphate backbone)