DNA Structure and Replication

Question 1

What circumstantial evidence is there to support the presence of DNA?

Answer 1

Nuclei staining put DNA in the correct place.

Question 2

What did Griffith prove?

Answer 2

That a chemical substance from one cell is capable of genetically transforming another cell.

Question 3

What was the chemical substance that transformed the non virulent R strain to a virulent strain?

Answer 3

DNA

Question 4

What was used to determine whether DNA or protein is the genetic material?

Answer 4

Bacteriophage T2

Question 5

What is the function of Bacteriophage T2?

Answer 5

It enters E.coli cells and converts them into virus making machines.

Question 6

How was it determined that DNA is the genetic material?

Answer 6

DNA of bacteriophage T2 enters the E.coli not proteins.

Question 7

What did Rosalind Franklin discover using x-ray diffraction?

Answer 7

The structure of DNA.

Question 8

What is Erwin Chargaff’s rule?

Answer 8

The number of A’s = number of T’s and the number of G’s = the number of C’s.

Question 9

What did Crick and Watson determine?

Answer 9

The double helix.

Question 10

How many nucleotides are there per turn?

Answer 10

10

Question 11

Which groove has the more accessible bases?

Answer 11

The major groove.

Question 12

How many hydrogen bonds are there between Guanine and Cytosine?

Answer 12

3

Question 13

How many hydrogen bonds are there between Adenine and Thymine?

Answer 13

2

Question 14

What is strand direction determined by?

Answer 14

Sugar phosphate bonds.

Question 15

What is semiconservative replication?

Answer 15

Replication where each new DNA molecule has one old strand and one new strand.

Question 16

Who proved semiconservative replication?

Answer 16

Meselson-Stahl

Question 17

How does replication happen in bacteria?

Answer 17

It proceeds bidirectionally from a single origin on a circular genome.

Question 18

How do eukaryotic chromosomes differ from prokaryotic?

Answer 18

They are much longer with multiple origins.

Question 19

In what direction does DNA grow?

Answer 19

5’-3’

Question 20

What does DNA polymerase bind to?

Answer 20

The template strand.

Question 21

How is DNA polymerase shaped?

Answer 21

Like an open right hand - the “palm” brings active site and substrate into contact and the “fingers” recognise the nucleotide bases.

Question 22

What does DNA polymerase require to start synthesis?

Answer 22

A 3’OH end.

Question 23

How is an RNA primer produced?

Answer 23

By primase binding to the template strand and synthesising a primer.

Question 24

What enzyme unwinds the DNA?

Answer 24

Helicase

Question 25

What keeps the strands separated?

Answer 25

Single stranded binding proteins.

Question 26

How does synthesis on the lagging strand occur?

Answer 26

Discontinuous okazaki fragments are lay down and a primer is lay down to provide a 3’ end.

Question 27

What identifies mismatches?

Answer 27

DNA polymerase and then exonuclease removes the nucleotide and adds the correct one.

Question 28

In what phase of the cell cycle does DNA synthesis take place?

Answer 28

S phase.

Question 29

What is the process of mismatch repair?

Answer 29

Proofreading misses the error, mismatch repair proteins identify and remove the nucleotide and some of the surrounding nucleotides, DNA polymerase I adds the correct nucleotides and ligase repairs the remaining nick.

Question 30

What is the process of excision repair?

Answer 30

The nucleotide is damaged by external factors, excision repair proteins remove the damaged nucleotide and others surrounding it, DNA polymerase adds the correct nucleotides and ligase repairs the remaining nick.