L6-8: DNA Structure, Replication and Mutation

Question 1

Four hypotheses of origin of life on earth

Answer 1

1. synthesis in reducing atmosphere
2. meteorites (panspermia)
3. synthesis in deep ocean vents
4. RNA

Question 2

what are control regions on DNA

Answer 2

specific sequences not in triplets

Question 3

diff. in the ribose b/w DNA and RNA

Answer 3

dna= h
rna= oh

Question 4

how are polymers of nucleic acids linked

Answer 4

5’ phosphate + 3’ OH

Phosphodiester bond

Question 5

what is Z dna

Answer 5

left handed

Question 6

two strands in replication

Answer 6

leading and lagging

Question 7

what is the short segments in lagging strand called

Answer 7

okazaki fragments

Question 8

what is the first step of DNA repliction

Answer 8

helicase unwinds at origin

Question 9

explain step 2: dna primase and rna primer

Answer 9

dna primase synthesises short short of RNA primer= adds several nucleotides to ss to kick off rpelication

Question 10

explain step 3: dna polymerase

Answer 10

DNA polymerase adds nucleotide to 3’ hydroxyl end of RNA primer

Question 11

explain step 4 b: lagging strand

Answer 11

okazaki fragments primed in several spots using RNA primer + dna polymerase adds nucleotides
dna ligase joined fragments by sugar phosphate backbone

Question 12

explain 4 proteins in replication machine

Answer 12

SS DNA binding proteins= stabalise ss
helicase= unwinds = ss
sliding clamp= holds dna polymerase on dna
clamp loader= assembles clamp using atp

Question 13

2 ways changes in DNA sequence occur

Answer 13

1. DNA replication errors

2. environmental factors

Question 14

what is DNAs high fidelity caused by

Answer 14

1. base pair structures
2. primer requirements of dna polymerase
3. dna polymerase proof reads

Question 15

3 types of environmental factors effecting dna sequences changing

Answer 15

chemical
radiation
mobile dna

Question 16

two forms of nucleotide instability

Answer 16

1. depurination: loss of G or A= gap

2. deamination= loss of amino group = C > U

Question 17

Two mutagenic chemical mutations

Answer 17

alkylation: electrophiles add alkyl groups to nitro bases
intercalation: compound inserts into double stranded helix

Question 18

wat does uv light do to dna

Answer 18

attach two adjacent thymine= thymine dimer

Question 19

two ways gamma and x rays attack dna bonds

Answer 19

directly
indirectly
= results in single and double strand breaking

Question 20

when do mobile genetic elements insert into dna

Answer 20

recombination

- breaking and rejoining of DNA during = nonhomogous recom + homo recom

Question 21

what are transposons (tn)

Answer 21

linear dna that insert into dna sequences

Question 22

two types of transposition mechanisms

Answer 22

1. cut and past

2. replicative transposition

Question 23

2 dna repair mechanisms

Answer 23

mismatch pair (correct dna polymerase mistakes)
homologous recombination = repairs double stranded brakes

Question 24

how does mismatch repair

Answer 24

'mis paired nucleotides'
four steps
1.  Excision by nucleases
2, Re-synthesis by repair DNA polymerase
3. Ligation of the DNA backbone by DNA ligase

Question 25

how does homologous recombination repair

Answer 25

exonuclease removes nucleotides ss 3' overhang and migrate into recipient rna polymerase = new strand rotation of crossed strands

Question 26

what is holliday junction

Answer 26

crossed strands during homo recom

Question 27

enzymes in hr

Answer 27

exonuclease + dna polymerase