DNA replication

Question 1

What are the two general features of DNA replication?

Answer 1

1. DNA is the storer of genetic information
2. Replication is semi-conservative

Question 2

Who first suggested that DNA could replicate?

Answer 2

Watson and Crick in a paper in 1953

Question 3

What does it mean to say that DNA replication is semi-conservative?

Answer 3

Each daughter strand receives one parental strand

Question 4

___________ are enzymes that catalyze the synthesis or polymerization of DNA from the appropriate dNTPs (deoxynucleotide triphosphates) in a sequence-dependent manner.

Answer 4

DNA polymerases

Question 5

What four things are required for DNA replication?

Answer 5

1. Enzyme - DNA polymerase
2. DNA
3. Monomers (i.e., dNTPs)
4. Primers

Question 6

The template strand is….?

Answer 6

The DNA strand being copied; it directs the incorporation of appropriate dNTPs into the growing strand

Question 7

DNA polymerase cannot initiate new chains; it can only add to pre-existing chains that contain a free ____ hydroxyl group.

Answer 7

3’

Question 8

DNA polymerase requires a free 3’ hydroxyl group for synthesis; therefore, DNA replication requires ______________.

Answer 8

RNA primers

Question 9

The polarity of DNA synthesis is very important. DNA is read in the ___ to __ direction and synthesized in the ___ to ___.

Answer 9

Read: 3’ to 5’

Synthesized: 5’ to 3’

Question 10

The mechanism of DNA replication involves a ____________________ attack by the 3’ hydroxyl on the alpha phosphate of the incoming dNTP. The reaction catalyzed is called a ____________________ as it synthesizes DNA based on complementary base pairing to a template DNA strand. DNA polymerase requires two ___ ions in the active site.

Answer 10

Nucleophilic attack

Phosphoryl group transfer reaction

Mg²⁺

Question 11

Explain the mechanism of DNA replication:

Answer 11

1. The 3’ hydroxyl group functions as a nucleophile, facilitated by the presence of Mg²⁺
2. The 3’ oxygen atom attacks the electrophilic alpha phosphate of the incoming dNTP
3. After attack, an unstable intermediate forms, requiring that the O-P reforms a double bound
4. The “kick back” causes the bond to break between the alpha phosphate and the oxygen atom of the beta phosphate
5. This results in the dNTP now connected via a phosphodiester bond and the release of inorganic pyrrophosphate, which will be cleaved into two inorganic phosphate molecules

Question 12

What is the purpose of Mg²⁺ in the formation of the phosphodiester bond?

Answer 12

It facilitates oxygen’s nucleophilic attack of the alpha phosphate

Question 13

DNA replication occurs at replication ____________. The lagging strand undergoes ____________ replication while the leading strand undergoes ____________ replication.

Answer 13

Forl

Discontinuous

Continuous

Question 14

You must be able to identify the direction of replication, the lagging strand, and the leading strand at a replication fork.

Answer 14

Question 15

DNA synthesis is semi-discontinuous and bidirectional. ______________________ means that one strand is synthesized continuously (the _________ strand) and the other is synthesized discontinously (the ____________ strand).

Answer 15

Semi-discontinous

Leading

Lagging