DNA Structure and Replication

Question 1

origin of replication

Answer 1

the point in the DNA at which replication begins; characterized by a particular sequence of nucleotides (the ORI sequence) containing a large number of A-T bonds

Question 2

ssDNA

Answer 2

single-stranded DNA; in DNA replication, the DNA after it is separated to serve as the template for replication

Question 3

dsDNA

Answer 3

double-stranded DNA; two DNA strands with complementary base-pair sequences joined by hydrogen bonds

Question 4

replication fork

Answer 4

point at which the two DNA strands begin to separate for replication

Question 5

replication bubble

Answer 5

gap in the DNA formed as the replication fork expands

Question 6

helicase

Answer 6

enzyme that binds to the ORI sequence and unwinds the dsDNA at replication forks

Question 7

single-strand binding proteins

Answer 7

proteins that bind to and stabilize the ssDNA after helicase unwinds it

Question 8

primase

Answer 8

enzyme that builds an RNA primer to begin DNA replication; one primer is used for the leading strand, and several primers are used on the lagging strand to create Okazaki fragments

Question 9

topoisomerase

Answer 9

enzyme that prevents the double helix from becoming “overwound” during DNA replication by breaking one strand, turning it, and then rejoining the strand together

Question 10

DNA polymerases

Answer 10

enzymes that synthesize new DNA strands in the 5’ to 3’ direction using the parental DNA is a template; in DNA replication, DNA polymerase III adds nucleotides to the 3’ end of the RNA primer, and DNA polymerase I removes the RNA primer and replaces it with DNA

Question 11

ligase

Answer 11

joins together fragments of DNA; in DNA replication, joins the newly replaced primer DNA to the leading strand and joins the Okazaki fragments together on the lagging strand

Question 12

sliding clamp

Answer 12

binds DNA polymerase III to the DNA, preventing the polymerase from detaching

Question 13

leading strand

Answer 13

newly formed ssDNA complementary to the parental DNA, synthesized continuously towards the replication fork as it expands

Question 14

lagging strand

Answer 14

complementary ssDNA synthesized with polymerase moving away from the replication fork; synthesized in several small segments called Okazaki fragments

Question 15

Okazaki fragment

Answer 15

a small segment of DNA formed on the lagging strand using an RNA primer