Question

As DNA replication continues and the replication bubble expands, the parental double helix is unwound and separated into its two component strands. This unwinding and separating of the DNA requires three different types of proteins: helicase, topoisomerase, and single-strand binding proteins. Sort the phrases into the appropriate bins depending on which protein they describe.

Answer 1

Helicase -

breaks H-bonds between bases

binds at the replication fork

Topoisomerase

breaks covalent bonds in DNA backbone

binds ahead of the replication fork

Single-Strand Binding Protein

prevents H-bonds between bases

binds after the replication fork

Step-by-step explanation:

At each replication fork, helicase moves along the parental DNA, separating the two strands by breaking the hydrogen bonds between the base pairs. (This makes the two parental DNA strands available to the DNA polymerases for replication.) As soon as the base pairs separate at the replication fork, single-strand binding proteins attach to the separated strands and prevent the parental strands from rejoining.

As helicase separates the two parental strands, the parental DNA ahead of the replication fork becomes more tightly coiled. To relieve strain ahead of the replication fork, topoisomerase breaks a covalent bond in the sugar-phosphate backbone of one of the two parental strands. Breaking this bond allows the DNA to swivel around the corresponding bond in the other strand and relieves the strain caused by the unwinding of the DNA at the helicase.

Answer 2

• helicase - breaks H-bonds between bases; binds at the replication fork
• topoisomerase - breaks covalent bonds in DNA backbone; binds ahead of the replication fork
• single-strand binding - prevents H-bonds between bases; binds after the replication fork

Step-by-step explanation:

As DNA replication continues and the replication bubble expands, the parental double helix is unwound and separated into its two component strands. This unwinding and separating of the DNA requires three different types of proteins:

• helicase - breaks H-bonds between bases; binds at the replication fork
• topoisomerase - breaks covalent bonds in DNA backbone; binds ahead of the replication fork
• single-strand binding - prevents H-bonds between bases; binds after the replication fork