What do restriction enzymes do?
a. they join different dna molecules together.
b. they distinguish protein-coding sequences from noncoding sequences.
c. they amplify specific dna sequences.
d. they cut dna at specific sequences.
e. they carry dna from the cells of one species into the cells of another species.

D. They cut DNA at specific sequences.

Explanation - Restriction enzymes are those enzymes that identify specific DNA sequences and cleaves them at that particular region. Restriction enzyme mainly cleaves DNA and are sometimes directed by RNA to make the incision.

Restriction enzymes are used to carry out many biotechnology related experiments. They are widely used to study DNA or genome of various organism. For different restriction sites, different restriction enzymes are there and each enzyme are chosen based on the study under consideration.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.