unit 1

Question 1

state how Griffith provided evidence for the transforming principle

Answer 1

• heat killed smooth pneumococcus + live rough pneumococcus

- mice died

Question 2

how did the experiments of Avery, McCarty and MacCleod support Griffith’s experiment?

Answer 2

• they added protease and DNase
• with protease, transformation takes place
• with DNase, it doesnt

Question 3

how did Hershey & Chase provide evidence for DNA as genetic material?

Answer 3

• radiolabelled phage grown in 32S and 32P
• separated genetic material from phage by centrifuge
• empty phage supernatant contained 32S, bacterial pellet 32P

Question 4

In Hershey & Chase’s experiments, what is the significance of the bacterial pellet containing 32P?

Answer 4

proves that the genetic material is comprised of DNA, which contains phosphate, instead of proteins, which contain sulfur

Question 5

how does RNA and DNA differ in terms of bases?

Answer 5

RNA contains the pyrimidine base Uracil instead of Thymine

Question 6

what is a nucleoside?

Answer 6

a nitrogenous base covalently bonded to a sugar, without a phosphate group.

Question 7

which type of bond links the nitrogenous base and sugar in a nucleoside?

Answer 7

Beta-Glycosidic

Question 8

define nucleotide

Answer 8

a nitrogenous base, a sugar and 1-3 phosphate groups

Question 9

in the context of an anti-parallel strand of DNA, what is meant by polarity?

Answer 9

polynucleotides have a 5’ phosphate knob and a 3’ hydroxyl hole
allows us to tell which end is which

Question 10

what is the sequence hypothesis?

Answer 10

DNA backbone is invariant and identical, the only determining factor in the structure of a protein is the sequence of base pairs within it.

Question 11

how does an alpha-helix differ from a DNA helix?

Answer 11

DNA helices are right handed double helices

Question 12

what is the role of the phosphodiester backbone in DNA?

Answer 12

acts as a frame, allowing hydrogen bonds to successfully form between bases.

Question 13

what is meant by complementary base pairing?

Answer 13

specific purine and pyrimidine bases hydrogen bond to each other due to the high specificity of their structure

Question 14

how many base pairs are there is one helical turn?

Answer 14

10

Question 15

what is a major and minor group?

Answer 15

each turn of DNA has a major and minor groove, proteins bind to major grooves

Question 16

what properties does supercoiling give to the genetic material?

Answer 16

more compact, less viscous, less prone to breakage

Question 17

what are topoisomerases?

Answer 17

enzymes that interconvert topoisomers using ATP

Question 18

what is meant by hyperchromicity?

Answer 18

constituents of DNA have a higher UV absorption independently, hydrolysis of DNA leads to an increase in UV absorption

Question 19

what are exonucleases?

Answer 19

enzymes that degrade DNA strands at one end or the other

Question 20

what are endonucleases?

Answer 20

enzymes that cut double stranded DNA at internal sites

Question 21

how do sequence specific endonucleases generate blunt ends?

Answer 21

cutting straight across

Question 22

how do sequence specific endonucleases generate sticky ends?

Answer 22

making staggered cuts

Question 23

what are the requirements of DNA Polymerase I?

Answer 23

dNTPs, Mg, template strand and primer strand with 3’ hydroxyl

Question 24

what other functions does DNA polymerase I have?

Answer 24

3’ -5’ prime exonuclease (can go back and remove a nucleotide) and nuclease activity (can find single stranded breaks and remove them without breaking progressivity)

Question 25

which DNA polymerase is most processive?

Answer 25

DNA Polymerase III

Question 26

which feature of DNA Polymerase III allows it to slide along the DNA?

Answer 26

2x beta sub units which form a ‘sliding clamp’ around DNA