Question

question 7 of 20 : select the best answer for the question. 7. in the dna double helix, how are the two strands of dna held together? a. hydrogen bonds between sugar groups and phosphate groups hold the two strands of dna together. b. chemical bonds between sugar groups and phosphate groups hold the two strands of dna together. c. hydrogen bonds between the base pairs hold the two strands of dna together. d. chemical bonds between base pairs hold the two strands of dna together. mark for review (will be highlighted on the review page)

Explanation:

To determine the correct answer, we analyze the structure of DNA:

• The sugar - phosphate groups form the backbone of each DNA strand and are connected by covalent (chemical) bonds within a strand, not between the two strands. So options A and B are incorrect as they suggest bonds between sugar and phosphate groups hold the two strands together.
• The two strands of the DNA double helix are held together by hydrogen bonds between the complementary base pairs (adenine - thymine and guanine - cytosine). Chemical bonds (like covalent bonds) are not responsible for holding the two strands together, so option D is incorrect. Option C correctly states that hydrogen bonds between base pairs hold the two strands together.

Answer:

C. Hydrogen bonds between the base pairs hold the two strands of DNA together.