Lecture 11 - DNA Chemistry and Replication

Question 1

Is DNA the genetic material?

Answer 1

yes

• carry information
• replicate faithfully and transmit info
• have variation

Question 2

What was the Griffiths Transformation Experiment?

Answer 2

Q: “is there a transforming principle?”

• took an R strain (non-virulent) and an S strain (virulent) and injected them into mice
• conclusion: there is an abiotic transforming principle

Question 3

What was the Avery, MacLeod, and McCarty Experiment?

Answer 3

Q: “what is the transforming principle?”

• repeated Griff’s experiment and added enzymes to specifically degrade different macromolecules
• all mice died except for the DNase experiment
• conclusion: DNA is the transforming principle

Question 4

What was the Hershey and Chase Experiment?

Answer 4

Q: “is DNA the universal transforming principle?”

• used phage and radioactivity to differentially label proteins vs. DNA
• conclusion: DNA is the universal transforming principle

Question 5

Who proposed that DNA was a double helix, sugar-phosphate backbone, and complementary base pairing?

Answer 5

Watson and Crick in 1953

Question 6

What are the characteristics of DNA?

Answer 6

• antiparallel
• complementary base pairing
• doubled stranded
• bases point in
• purine always pairs with a pyrimidine

Question 7

What forces stabilize DNA?

Answer 7

• phosphodiester bonds (covalent)
• hydrogen bonding (base pairing)
• hydrophobic base stacking

Question 8

What is DNA replication?

Answer 8

• happens in the S-phase of the cell cycle

- DNA strand are complementary

Question 9

What were the three possible models in the Meselson-Stahl Experiment?

Answer 9

1. conservative
2. semi-conservative
3. dispersive

Question 10

How was the Meselson-Stahl experiment performed?

Answer 10

• used radioactivity to change the molecule mass of N
• N14 = “normal”
• N15 = “heavy”
• bacteria were grown in N15 and then went through one round of replication in N14
• disproved conservative but the other two models have to go through a second round before semi-conserative was accepted

Question 11

What direction is DNA polymerized?

Answer 11

5’ —> 3’

- adding nucleotides to 3’ end

Question 12

What are the three rules to understand DNA replication?

Answer 12

1. DNA is antiparallel
2. DNA polymerase only extends from 5’ to 3’
3. DNA polymerase requires an existing 3’OH

Question 13

What is the leading strand?

Answer 13

• synthesized in the same direction as the fork opening

Question 14

What is the lagging strand?

Answer 14

• synthesized in the opposite direction of the fork opening

- contains Okazaki fragments

Question 15

What does helicase do?

Answer 15

• unzips DNA

Question 16

What are single-stranded binding proteins?

Answer 16

• sit on the outside of the leading and lagging strands

Question 17

What does primase do?

Answer 17

• adds an RNA primer

Question 18

What does DNA pol III do?

Answer 18

• extends off the primer making DNA (5’ -> 3’)

Question 19

What does DNA pol I do?

Answer 19

• removes a primer and replaces that section with DNA

Question 20

What does ligase do?

Answer 20

• joins fragments