L12- DNA review

Question 1

a replicate chromosome is what shape

Answer 1

x-shaped

- two chromatids

Question 2

shot arms

Answer 2

p arms

Question 3

long arms

Answer 3

q arms

Question 4

telomere found

Answer 4

on the ends of chromosomes

Question 5

how many diff types of chromosomes

Answer 5

4

Question 6

name diff types of chromosomes

Answer 6

1) Metacentric
2) submetacentric
3) acrocentric
4) telocentric

Question 7

metacentric

Answer 7

centromere in the middle of the p and q arms

Question 8

submetacentric

Answer 8

centromere further up P arm

Question 9

acrocentric

Answer 9

centromere even further up p arm

Question 10

telocentric

Answer 10

centromere right at top of p arm

Question 11

DNA helicase

Answer 11

unwinds and separates double stranded DNA as it moves along the DNA. It forms the replication fork by breaking hydrogen bonds between nucleotide pairs in DNA.

Question 12

replication only progresses in

Answer 12

5’ to 3’ end

Question 13

DNA polymerase has to add to

Answer 13

3’ end

Question 14

primer binds to the

Answer 14

3’ end of the strand- acting as a starting point for replication by polymerase

Question 15

primers are

Answer 15

oligonucleotides generated by DNA primase

Question 16

once both continuous and discontinuous strands are formed exonucleases

Answer 16

remove all RNA primers from original strand- primers then replaced with appropriate bases

Question 17

function of exonuclease domain in DNA polymerase

Answer 17

• RNA degradation (primers)
• DNA proofreading
  o Work by scanning directly behind as DNA polymerase adds new nucleotides to the growing strand
• Transcriptional regulation

Question 18

exonuclease cleave…

Answer 18

nucleotides off one at a time from the end (exogenous) of the polynucleotide chain by hydrolysing phosphodiester bonds

Question 19

exonuclease and cancer

Answer 19

• If exonucleases are mutated they will not perform their regular function of proofreading DNA and cleaving wrongly transcribed DNA
  o E.g. a gene controlling cell division may be mutated and the exonuclease would not be able to recognise and correct it
   E.g. tumour suppressor gen

Question 20

DNA gyrase (topoisomerase)

Answer 20

unwinds and rewinds DNA strands to prevent the DNA from becoming tangled or supercoiled.

Question 21

DNA ligase

Answer 21

• joins DNA fragments together by forming phosphodiester bonds between nucleotides.

Question 22

DNA polymerases can only make DNA in the ……. why may this pose a problem

Answer 22

5’ to 3’ direction, and this poses a problem during replication.

A DNA double helix is always anti-parallel; in other words, one strand runs in the 5’ to 3’ direction, while the other runs in the 3’ to 5’ direction.

This makes it necessary for the two new strands, which are also antiparallel to their templates, to be made in slightly different ways.

Question 23

leading strand

Answer 23

runs 5’ to 3’ towards the replication fork.

This strand is made continuously, because the DNA polymerase is moving in the same direction as the replication fork.

This continuously synthesized strand is called the leading strand.

Question 24

DNA demythylation and histone acetylation

Answer 24

increases amount of active chromatin (euchromatin)

Question 25

methylation of histone groups

Answer 25

decreases amount of active chromatin, increasing amount of heterochromatin

Question 26

why do major and minor grooves exist in alpha helical structure

Answer 26

Two different types of grooves as sugar is asymmetrically bonded to base pair
- DNA- protein binding will bind to major groove- more space to binds

Question 27

Question 2: Azidothymidine (AZT) is used to treat HIV and AIDS and has the structure shown below (the azido group is shaded). Suggest how the drug works.

Answer 27

AZT looks like a funny deoxyribonucleoside

• Therefore can be incorporated into a DNA strand
• Forms hydrogen bonds with other bases (similar shape to thymine)
• AZT lacks 3’OH therefore elongation by polymerase cannot occur after

Question 28

a high does of AZT would

Answer 28

Would stop all DNA replication- including human. Therefore cells with a high turnover rate e.g. cells that line the gut will not be renewed
- Can cause digestive problems