DNA lecture 1

Question 1

What did Watson and Crick Propose

Answer 1

Semi-conservative replication.

• Parent strand
• Daughter strand

Hybrids of the new and old strand

Question 2

Who proved the Watson and Crick hypothesis?

Answer 2

Messelson and Stahl who conducted an experiment using radioactive nitrogen taken up within Ecoli.

Question 3

What did the experiment involve?

Answer 3

Centrifuged the Ecoli bacteria and then measured the density of the resulting DNA strands. Radioactive 15N has a greater density and would sink to the bottom of the test tube.
Then would compare by the degree of sinking within the test tube:
- Parent strand vs Daughter Strand vs Hybrid strand

Question 4

What determines where DNA replication occurs in eukaryotic cells?

Answer 4

The origins of replication

Question 5

What is involved within DNA replication

Answer 5

To antiparallel complementary DNA strands

Question 6

What determines the direction of the DNA strands?

Answer 6

Sugar in the carbons - exposed 3` OH group

Question 7

What initiates DNA replication

Answer 7

DNA polymerase III = polymerisation of nucleotides

Question 8

What does DNA Polymerase III require?

Answer 8

4 dNTPs, template strand & primer with 3` OH group

Question 9

What makes RNA Primers

Answer 9

RNA Primase/ polymerase

Question 10

What direction is complementary DNA strands synthesised in

Answer 10

5 to 3

Question 11

What direction do the DNA enzymes move in?

Answer 11

3 to 5

Question 12

Does one or both strands act as templates

Answer 12

Both strands behave as templates

Question 13

What are two important components of semi-conservative replication

Answer 13

Bidirectional and simultaneous DNA replication

Question 14

What do we need to overcome in DNA replication synthesis

Answer 14

The need for complementary strands to be made 5` to 3. We overcome this through discontinuous synthesis.

Question 15

What is it easier to make a complementary DNA strand for: leading or lagging strand

Answer 15

Leading strand = continuous synthesis

Question 16

What are the DNA fragments called that are made in discontinuous DNA synthesis

Answer 16

Okazaki fragments

Question 17

How did we prove the Okazaki fragments presence?

Answer 17

Okazaki used H3-dnTP (ie radioactive) which was incorporated into the presence of the DNA for 5 second pulses. Break up strands and found more H3 in continuous strand of leading strand and less in the lagging strand during discontinuous synthesis in DNA replication.

Question 18

What does helicase do

Answer 18

Unwinds DNA double helix by breaking double bonds between complementary DNA base pairs

Question 19

What form of DNA polymerase is responsible for exonuclease activity?

Answer 19

DNA Polymerase I

Question 20

What does DNA polymerase I do?

Answer 20

locates and removes RNA primers

Question 21

What does DNA ligase do?

Answer 21

Adds phosphate into the gaps of the phosphate sugar backbones, where the RNA primers originally where.

Question 22

What does RNA Primers initiate?

Answer 22

DNA replication

Question 23

What do we call the protein complex of DNA replication

Answer 23

Replisome

Question 24

What determines the origin of replication

Answer 24

Regions where there are lots of adenine and thymine nitrogenous bases = 2 hydrogen bonds and therefore easier to separate.

Question 25

Does proof reading occur

Answer 25

Yes

Question 26

Number of template strands

Answer 26

2

Question 27

Size of templte

Answer 27

Whole strand of complementary DNA

Question 28

Products

Answer 28

DNA

Question 29

Nucleotide substrate

Answer 29

dNTPs