Question

question 7 of 15
which statement below accurately describes the 3 and 5 ends of dna?
a. they represent different parts of the phosphate group and determine where the pentose sugars bond to form a linear polymer.
b. one end is the phosphate group, and one end is the nitrogen base, and these determine how mrna is synthesized.
c. they consist of two oxygen atoms on the 5 - carbon sugar and determine whether the nucleic acid is a purine or pyrimidine.
d. they are carbons in the pentose sugar involved in the sugar - phosphate linkage and determine the direction of transcription.

Explanation:

• In DNA, the 3' and 5' ends refer to specific carbons in the pentose sugar (deoxyribose).
• The sugar - phosphate linkage occurs between the 3' carbon of one deoxyribose and the 5' carbon of the next deoxyribose.
• This orientation (3' to 5' or 5' to 3') is crucial for processes like transcription (synthesis of mRNA from DNA). For example, RNA polymerase reads the DNA template strand in the 3' to 5' direction and synthesizes mRNA in the 5' to 3' direction.
• Option A is incorrect because the 3' and 5' are not about different parts of the phosphate group.
• Option B is wrong as neither end is a nitrogen base.
• Option C is incorrect since the 3' and 5' are not about oxygen atoms determining purine or pyrimidine nature.

Answer:

D. They are carbons in the pentose sugar involved in the sugar - phosphate linkage and determine the direction of transcription.