3

Question 1

Purines?

Answer 1

guanine and adenine

Question 2

pyrimidines?

Answer 2

Thymine,Cytosine and Uracil

Question 3

Bond between Thymine and Adenine:

Answer 3

2 bonds: 1= c=o of T and NH2 of A 2=NH of T and N of A

Question 4

Bond between Cytosine and Guanine

Answer 4

triple bond

Question 5

Explain DNA replication initiation steps and why replication can occur simultaneously along different locations in eukaryotes but not bacteria?

Answer 5

1) origins of replication are targeted by Initiator proteins
2) these then allow the other proteins necessary for DNA replication to bind the same region such as Helicase
2) Each helicase unwinds and separates the DNA helix into single-stranded DNA
3) As the DNA opens up, Y-shaped structures called replication forks are formed
4) These are extended in both directions as replication proceeds creating a replication bubble.

(In eukaryotes there are multiple ORIs which allow replication to occur simultaneously in hundreds to thousands of locations along each chromosome)

Question 6

Up to how many ORIS are they in a human cell?

Answer 6

100,000

Question 7

What genome organisation do archea have?

Answer 7

single circular chromosome

Question 8

Do archaea have plasmids?

Answer 8

yes

Question 9

Do Archaea’s circular chromosomes have multiple ORIs?

Answer 9

yes

Question 10

Can Archaea produce asexually and how?

Answer 10

Yes they can reproduce asexually by binary reproduction,binary fission,fragmentation or budding.

Question 11

What is Archaea cell division process controlled by?

Answer 11

The cell cycle.

Question 12

In the cell division process in Archaea what happens to the chromosomes?

Answer 12

they are replicated to produce 2 daughter chromosomes which are then separated when the cell divides

Question 13

Do Archaea have DNAP that resemble those of eukaryotes or bacteria?And the same for proteins?

Answer 13

the DNAP resemble those of eukaryotic enzymes however the proteins involved in irect cell division are similar to those in bacterial systems.

Question 14

Before synthesis is initiated in all life what group needs to be free?

Answer 14

a free 3’OH group

Question 15

What is the primase used by Archaea highly derived from?

Answer 15

The primase used by archaea is a highly derived version of the RNA recognition motif (RRM). It is structurally similar to viral RNA dependent RNA polymerases, reverse transcriptases, cyclic nucleotide generating cyclases, and DNA polymerases involved in DNA replication and repair. Once the RNA primase has performed its job, DNA synthesis continues in a similar fashion by which the eukaryotic system and the DNA is replicated.

Question 16

Explain the difference between the leading and the lagging strand.

Answer 16

The leading strand is the template strand of the DNA double helix that is oriented so that the replication fork moves along it in the 3’ to 5’ direction. The lagging strand is the strand of the template DNA double helix that is oriented so that the replication fork moves along it in a 5’ to 3’ manner.

Question 17

What do initiator proteins allow?

Answer 17

DNA to melt ≪ 90°C

Question 18

What does helicase do?

Answer 18

continues melting using ATP

Question 19

what is the error rate of DNA replication in E.coli and homosapiens?

Answer 19

10^-9

Question 20

what is the speed of replication in e.coli?

Answer 20

1,000 nt s^-1

Question 21

what is the speed of replication in Homo sapiens?

Answer 21

50 nt s^-1

Question 22

what are ORI’s rich in?

Answer 22

AT rich

Question 23

nucleoside

Answer 23

sugar, base no phosphate

Question 24

What is the Klenow fragment?

Answer 24

Klenow fragment is part* of the bacterial DNAP-I repair polymerase used as a model system. Primer-removing exonuclease domain removed by hydrolysis.
Shaped like a right hand

Question 25

which bases are capable of amino-imino ro keto-enol tautomery?

Answer 25

All four bases are capable of either of these therefore are prone to these sort of lesions.

Question 26

Why does DNAP have to be unidirectional?

Answer 26

The DNAP has to be unidirectional because during 5ʹ3ʹ synthesis it is the dNTPs that bring in the energy (P-P-P group) needed to make the new phosphodiester-bond in the backbone of the DNA. When the exonuclease removes a mismatched base it exposes a ‘clean’ 3ʹ OH group, to which another dNTP can be attached, so polymerisation can immediately recommence after proofreading activity. However, if the strand were synthesised in the 3ʹ5ʹ direction, it would be the P-P-P already on the daughter strand that would provide the energy for polymerisation. Removal of a mismatched base would result in a ‘clean’ 5ʹ OH group, which would terminate polymerisation, so you’d need some complex and inefficient system to re-add the P-P-P and re-start polymerisation.

Question 27

Components of the replisome?

Answer 27

DNAP,helicase, primase,priming site and primer.

Question 28

Explain eukaryotic termination?

Answer 28

ends at telomere region. Ends are removed until genes are affected

Question 29

Where do you find telomerases?

Answer 29

stem and sex cells