Biology DNA Structure and Replication Flashcards

During replication, the lagging strand is synthesized as Okazaki fragments because:

Answer: DNA polymerase can only add nucleotides in the 5' to 3' direction, which runs away from the fork on that strand

Since DNA polymerase synthesizes only 5'→3', the lagging strand template (running 5'→3' toward the fork) must be copied in discontinuous fragments.

What is the role of single-strand binding proteins (SSBPs) during DNA replication?

Answer: They stabilize the unwound single strands and prevent reannealing

SSBPs coat the separated single-stranded DNA at the replication fork, keeping the strands apart so they can serve as templates.

The Watson-Crick model of DNA describes its structure as a:

Answer: Right-handed antiparallel double helix

Watson and Crick described DNA as a right-handed antiparallel double helix stabilized by hydrogen bonds between complementary bases.

In the Meselson-Stahl experiment, which replication model was supported?

Answer: Semi-conservative replication

Meselson and Stahl showed that after one generation, all DNA contained one heavy and one light strand, confirming the semi-conservative model.

Which purine base pairs with cytosine in DNA?

Answer: Guanine

Guanine (a purine) pairs with cytosine (a pyrimidine) via three hydrogen bonds in the DNA double helix.

What is a replication origin (ori)?

Answer: A specific DNA sequence where replication is initiated

A replication origin is a specific DNA sequence where replication machinery assembles and strand separation begins.

Topoisomerases relieve replication stress by:

Answer: Cutting and rejoining DNA to relieve supercoiling tension ahead of the replication fork

As helicase unwinds DNA, positive supercoils build up ahead of the fork; topoisomerases cut the DNA to relieve this torsional stress and then reseal it.