Structure of DNA
What are the building blocks of DNA called?
Nucleotides
Which enzyme unwinds and separates the DNA strands?
Helicase
What is the first step of DNA replication?
The DNA double helix unwinds and separates
A phosphate group, a deoxyribose sugar, and a nitrogen base
Which enzyme adds new nucleotides to the growing DNA strand?
DNA polymerase
What happens after the DNA strands separate?
RNA primers are added to provide starting points for DNA polymerase
Which two molecules form the "backbone" of the DNA double helix?
Sugar and phosphate groups
Which enzyme joins Okazaki fragments on the lagging strand?
DNA ligase
Why is replication called “semi-conservative”?
Each new DNA molecule has one old strand and one new strand
Which nitrogen bases pair together in DNA, and how many hydrogen bonds connect each pair?
Adenine pairs with thymine (2 bonds), cytosine pairs with guanine (3 bonds)
Which enzyme creates a short RNA segment that provides a starting point for DNA synthesis?
Primase
What are Okazaki fragments, and where do they form?
Short DNA fragments are formed on the lagging strand during replication
Why are the two strands of DNA described as “antiparallel”?
Because they run in opposite directions: one 5’→3’, the other 3’→5’
Which enzyme helps relieve tension ahead of the replication fork by cutting and rejoining DNA strands?
Topoisomerase (or DNA gyrase)
In what direction is the leading strand synthesized compared to the lagging strand?
The leading strand is synthesized continuously toward the replication fork; the lagging strand is synthesized discontinuously away from the fork