DNA Chemistry and Replication

Question 1

What was the question asked in Griffiths Transformation Experiment?

Answer 1

Is there a transforming principle?

Question 2

Explain briefly how Griffiths underwent his experiment

Answer 2

Took rough and smooth strains, S was virulent and R was not. He injected them both into mice, the S strain killed the mouse. A heat killed S strain did not kill the mouse, but when mixed with R strain it did. This is because the R strain picked up the ability to cause disease from the environment (it transformed).

Question 3

What was Avery, MacLeod and McCarty’s experimental question?

Answer 3

What is the transforming principle?

Question 4

Explain Briefly how A, M, M underwent their experiment

Answer 4

Used different enzymes for degradation of cellular components (protease, Dnase, Rnase) Injected mice with heat killed S strain and R strain, the one with Dnase lived. Therefore DNA is the transforming principle, not proteins.

Question 5

What was Hershey and Chases question

Answer 5

Is DNA the universal transforming principle?

Question 6

Briefly explain H and C’s experiment

Answer 6

Used virus that infects bacteria (phage) to label proteins and DNA (S35 for proteins, P32 for DNA), found that the viral DNA enters the bacterial cell and the viral proteins do not (DNA’s pellet was radioactive)

Question 7

What is Chargaffs rule

Answer 7

%A=%T

%C=%G

Question 8

What did James Watson and Francis Crick discover

Answer 8

• DNA is a double helix (used work of others: Chargaff and Rosalind Franklin)
• A pairs with T, C pairs with G

Question 9

What are the three forces that stabilize DNA

Answer 9

1. Phosphodiester bonds
2. H-bonds
3. Hydrophobic base pairing

Question 10

When does DNA replication occur

Answer 10

S phase

Question 11

What did Meselson-Stahl attempt to detemine

Answer 11

Is DNA replication conservative, semiconservative or dispersive (can you picture the models in your head?)

Question 12

Briefly Describe Meselson-Stahl’s experiment

Answer 12

Used radioactivity to change molecular mass of N (N15= heavy nitrogen). One round of replication in N14 lead to observed intermediate band, conservative rep was disproved. Second round of replication in N14 led to one N14 band and one N14.5 band. Rules out dispersive cause we would have expected N14.25 band.

Question 13

What direction is DNA polymerized

Answer 13

5’ -> 3’ (nucleotides added to 3’ end)

Question 14

What is deoxyribonucleotide?

Answer 14

substrate of replication

Question 15

What is the enzyme of replication and what does it do

Answer 15

DNA polymerase

catalyzes phosphodiester bond formation

Question 16

What enzyme unwinds the double helix

Answer 16

helicase

Question 17

What is the role of DNA polymerase III

Answer 17

Adding nucleotides (in the 3’ to 5’ direction)

Question 18

What keeps the bubble unwound?

Answer 18

Single stranded binding proteins

Question 19

The ______ strand is synthesized discontinuously in small fragments called _______ __________.

Answer 19

1. lagging strand

2. okazaki fragments

Question 20

What connects the okazaki fragments?

Answer 20

DNA ligase

Question 21

What is the role of primase in replication

Answer 21

Synthesizes an RNA primer at 5’ end of lead strand and each okazaki fragment.

Question 22

What is the role of polymerase I?

Answer 22

Remove RNA nucleotides that primase put at the 5’ end and replaces them with DNA nucleotides