Lecture 8. DNA Replication

Question 1

Length of DNA in E. coli

Answer 1

1.6mm

Question 2

Length of an E. coli cell

Answer 2

1-2μm

Question 3

How is DNA compacted in the cell

Answer 3

By looping and supercoiling

Question 4

Total length of DNA in each nucleus of a human cell

Answer 4

~2.2m

Question 5

Diameter of nucleus in humans

Answer 5

~6μm

Question 6

Nucleosome

Answer 6

DNA + histone

Question 7

Predictions from Watson-Crick model

Answer 7

1. Strands must be antiparallel
2. DNA replication should be semi-conservative

Question 8

Who described CsCl equilibrium density gradient centrifugation and when was it described?

Answer 8

Meselson and Stahl, 1958

Question 9

What does CsCl equilibrium density gradient centrifugation do to molecules?

Answer 9

Separates molecules Andes on their densities

Question 10

What was ‘the most beautiful experiment’?

Answer 10

The experiment that showed that DNA replication is semi-conservative

Question 11

Who discovered DNA polymerase and when was it discovered?

Answer 11

Arthur Kornberg, 1957

Question 12

DNA polymerase I (Pol I) functions

Answer 12

New strands are extended in the 5’ → 3’ direction by polymerase
Pol I has editing/proof-reading functions and can or react mistakes

Question 13

What enzyme is essential for DNA replication in E. Coli?

Answer 13

Pol III

Question 14

What were the conclusions drawn from the nucleotide incorporation experiments?

Answer 14

dNTPs (deoxynucleotide triphosphates) are required for DNA synthesis but DNA contains only mono-phosphate residues so pyrophosphate must be released

Question 15

How was DNA polarity tested?

Answer 15

Nucleotide insertion of a radioactive sugar-proximal phosphate that became attached to the nearest neighbour after the ester bonds between the phosphates were broken