16. During DNA replication, all of the following steps occur EXCEPT

a. enzymes proofread new strands for errors and correct them
b. the double helix is unwound by DNA polymerases
c. base-pairing rules determine which nucleotide is added to new strands
d. each strand of a DNA double helix is copied, forming two identical double helixes
I've done some research and I think it's B, but I'm not 100% sure

To determine the correct answer, let's review the process of DNA replication and eliminate the options one by one:

a. Enzymes proofread new strands for errors and correct them: This step, known as proofreading, does occur during DNA replication. Enzymes called DNA polymerases examine the newly synthesized strands and correct errors by removing incorrect nucleotides and replacing them with the correct ones.

b. The double helix is unwound by DNA polymerases: This statement is not accurate. The unwinding of the double helix during DNA replication is actually performed by an enzyme called helicase, not DNA polymerases. Therefore, option B is incorrect.

c. Base-pairing rules determine which nucleotide is added to new strands: This statement is true. During DNA replication, the base-pairing rules dictate that adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). This ensures that the newly synthesized strands are complementary to the original strands. Therefore, option C is a valid step in DNA replication.

d. Each strand of a DNA double helix is copied, forming two identical double helices: This statement is also true. DNA replication is a semiconservative process, meaning that each original strand serves as a template for the synthesis of a new complementary strand. As a result, two identical double helices are formed. Therefore, option D is a valid step in DNA replication.

Based on this analysis, the correct answer is option B - "the double helix is unwound by DNA polymerases."

You are correct! During DNA replication, all of the following steps occur except for b. the double helix is unwound by DNA polymerases.

In DNA replication, the double helix is unwound by an enzyme called helicase, not DNA polymerases. DNA polymerases are responsible for adding nucleotides to the newly synthesized strands based on the base-pairing rules (c). Enzymes also proofread the new strands for errors and correct them (a). Finally, each strand of the DNA double helix is copied, forming two identical double helices (d).

enzyme helicase, what does it do?

recosider d, and be a lawyer on how it is worded: Each double-stranded DNA helix is made of one new strand of DNA and one original strand of DNA.