DNA Replication

Question 1

Base Pairs:

Adenine–

Guanine–

Cytosine–

Thymine–

Answer 1

Adenine– –Thymine

Guanine– – –Cytosine

Cytosine– – –Guanine

Thymine– –Adenine

*Note: The number of “–” indicates the number of hydrogen bonds between each nitrogenous base pair.

Question 2

Antiparallel sugar-phosphate backbone

Answer 2

The each sugar-phosphate backbone of DNA is antiparallel with respect to the other.

3’——–>5’

5’——–>3’

Question 3

DNA backbone composition and linkages

Answer 3

Sugar and phosphate compose the backbone of DNA. They are linked together by phosphodiester linkages.

Question 4

Semiconservative model of DNA

Answer 4

Recombinant or semiconservative DNA is formed when two parental strands split and joins two new strands. So each of the two daughter strands of DNA includes one parental strand and one new strand.

Question 5

Origins of replication

Answer 5

Eukaryotic DNA: There are multiple orginins of replication sites.

Prokaryotic DNA: Single origin of replicatoin.

Question 6

Replication Fork

Answer 6

The point in which DNA Helicase unwinds the two strands of DNA.

Question 7

Template Strands

Answer 7

The two parental strands that are broken apart by DNA Helicase and are used as templates to make complementary strands of new DNA ultimately forming two daughter strands.

Question 8

Helicases

Answer 8

enzymes that unwind the double helix forming the replications forks and seperating the parental strands – template strands are formed.

Question 9

Helicases

Answer 9

Enzymes that unwind the double helix forming the replication forks and seperating the two parental strands into template strands.

Question 10

Single Strand Binding Proteins

Answer 10

bind to unpaired DNA strands to prevent them from rejoining.

Question 11

Topoisomerase

Answer 11

Breaks, swivles, and rejoins parental DNA because the strain of helicase unwinding can cause damage to the strand.

Question 12

DNA Polymerase

Answer 12

catalyzes synthesis of new DNA by adding nucleotides to a preexisting chain. Requires a primer that is synthesized by primase. The DNA Polymerase also requires a template strand so that it can synthesize a complementary strand that will bind accordingly.

Question 13

Leading Strand

Answer 13

DNA replicatoin for the leading strand is continuous. DNA Polymerase travels in the 3’—->5’ direction on the template strand thus forming a complementry strand that is in the 5’——>3’ direction.

Question 14

Lagging Strand

Answer 14

DNA replicatoin is fragmented on the lagging strand. Because the lagging strand travels in the 3’——>5’ direction on the template strand and forms the complementry strand in the 5’——–>3’ direction, primers must be added between fragments.

Question 15

Okazaki Fragments

Answer 15

The fragments of complementry strand DNA on the lagging strand.

Question 16

Ligase

Answer 16

Joins the Okazaki fragments together so that one complete complementry strand is formed.

Question 17

Mismatch Repair

Answer 17

Other enzymes remove/replace incorrectly paired nucleotides that stem form replication errors.

Question 18

Nuclease

Answer 18

A DNA-cutting enzyme that cuts out damaged or mismatched nucleotide sequences. The gap that gets cut out is filled with nucleotides using the undamaged strand as a template so that a complementry strand can be formed. An example is the nucleotide excision repair (see your text book page 258 for example).