dna structure and replication

Question 1

name the purines

Answer 1

A and G

Question 2

name the pyrimidines

Answer 2

T and C

Question 3

what makes up the nucleotides

Answer 3

base
phosphate
sugar

Question 4

what direction does the DNA strand run in?

Answer 4

5 prime to 3 prime

Question 5

what is at the 5 prime end?

Answer 5

a free phosphate group

Question 6

what is at the 3 prime end?

Answer 6

an unlinked OH group

Question 7

how many bonds do G and C form?

Answer 7

3

Question 8

how many bonds do A and T form?

Answer 8

2

Question 9

how many rings do the purines form?

Answer 9

2

Question 10

how many rings do the pyrimidines form?

Answer 10

1

Question 11

what is transcription?

Answer 11

DNA –> RNA

Question 12

what is translation?

Answer 12

RNA -> protein

Question 13

how does DNA form nucleosomes

Answer 13

DNA wraps around histones which form nucleosomes

Question 14

what are the core histone proteins?

Answer 14

H2A, H2B, H3 and H4

Question 15

what does topoisomerase do?

Answer 15

enzyme which prevents the supercoiling of DNA during replication

Question 16

what do quinolones and fluoroquinolones do?

Answer 16

target topoisomerase which causes DNA to supercoil and break

Question 17

what are the linker histones?

Answer 17

H1 and H5

Question 18

what type of bacteria do quinolones target?

Answer 18

Aerobic gram positive and negative
some anaerobic gram negative
Tuberculosis

Question 19

what does Trimethoprim-sulfamethoxazole target?

Answer 19

nucleotide synthesis

Question 20

what type of bacteria does trimethoprim-sulfamethoxazole target?

Answer 20

Gram positive and negative

Question 21

describe how low level mistakes in the DNA replication process are corrected

Answer 21

editing occurs in the 3-5’ direction as DNA is made by DNA polymerase in the 5’-3’ direction

mispaired nucleotide removed and correct one added

Question 22

describe base excision repair?

Answer 22

• cytosine is deaminated to form a uracil
• a single mispaired base
  enzyme comes and removes the base and breaks the sugar-phosphate backbone
• DNA polymerase adds a new base and ligase seals it

Question 23

explain nucleotide excision repair

Answer 23

pyrimidine dimer forms (caused by radiation)
forms adduct
either 12 (bacteria) or 20 (humans) nucleotides are removed from the strand either side using helicase and nuclease

DNA polyermase and ligase replace missing segment

Question 24

explain how DNA mismatch repair works

Answer 24

error in the DNA forms
MutS and MutL binds
finds a break in the DNA and cuts it there and removes it
DNA repaired

Question 25

describe non-homologous end joining

Answer 25

accidental break in the DNA and forms an overhang

enzymes break away at the overhang until the strands can join together

Question 26

describe homologous end joining

Answer 26

loss of a segment of DNA

sequence completed by copying from a second chromosome

Question 27

what is the phenotype of xeroderma pigmentosum

Answer 27

skin cancer
UV sensitivity
neurological abnormalities

Question 28

what process is affected in xeroderma pigmentosum?

Answer 28

nucleotide excision repair

Question 29

what is the phenotype of a mutation of MutS and MutL?

Answer 29

colon cancer

Question 30

what process is affected in a mutation of MutS and MutL?

Answer 30

mismatch repair

Question 31

what can a defect in BRCA2 cause?

Answer 31

breast and ovarian cancer

Question 32

what process is affected in breast and ovarian cancer?

Answer 32

repair by homologous recombination

Question 33

what is the function of linker histones?

Answer 33

locks DNA into place

allows it to be condensed into chromatin

Question 34

what are okazaki fragments and why are they formed?

Answer 34

one DNA strand goes from 5 to 3 prime
DNA polymerase cant synthesise as its reading
this strand is the lagging strand and its synthesised discontinuously
RNA primers are added at the start of every segment so DNA polymerase adds bases here
these are okazaki fragments