Maintenance and use of genetic information

Question 1

Definition of replication fork

Answer 1

Area where DNA replication takes place

Consists of 2 strands of DNA, leading and lagging

Question 2

Definition of leading strand

Answer 2

Strand of template DNA that is continuously being replicated in the 3’-5’, to form a strand that is in the 5’-3’ direction

Question 3

Definition of the lagging strand

Answer 3

Strand of template DNA that is not continuously being replicated in the 5’-3’, to form a strand that is in the 3’-5’ direction

Question 4

Definition of Okazaki fragments

Answer 4

Short DNA sequence which is discontinuously sysntheisied, creates long lagging strand

Question 5

Definition of helicase

Answer 5

Unwinds DNA strands

Question 6

Definition of topoisomerase

Answer 6

Released supercoils in DNA which could snap and cause serious DNA damage

Question 7

Definition of single strand binding protein

Answer 7

Stabilizes single stranded DNA by preventing it from reforming a double helix

Question 8

Definition of primase

Answer 8

Makes RNA primer so DNA synthesis can begin

Question 9

Definition of DNA polymerase

Answer 9

Synthesizes DNA

Question 10

Definition of exonuclease

Answer 10

Removes RNA primer

Question 11

Definition of DNA ligase

Answer 11

Links adjacent Okazaki fragments

Question 12

Definition of mutations

Answer 12

Incorporation of incorrect nucleotides into new DNA chain

Question 13

Definition of end replication paradox

Answer 13

Small amount of DNA lost from each end of a linear chromosome after each round of DNA replication

Question 14

Definition of telomerase

Answer 14

Extends DNA without chromosomal template as it has its own RNA template

Question 15

Definition of point mutation

Answer 15

Single

Question 16

Definition of silent mutation

Answer 16

No effect, same AA formed due to degenerate nature of AA

Question 17

Definition of missense mutation

Answer 17

AA formed is different

Question 18

Definition of nonsense mutation

Answer 18

AA codon replaced by stop codon

Question 19

Definition of indel

Answer 19

Small scale insertions/deletions

Question 20

The cell cycle

Answer 20

G0
-quiescent

G1
-organelle duplication

S
-DNA synth

G2
-error check DNA

M
-mitosis

Question 21

Describe the steps taken to initiate and start DNA synthesis

Answer 21

Initiator proteins bind to specific sequences => unzipping

Replication fork formation
DNA helicase = breaks HB
Single strand binding protein = stop reformation of helix
Topoisomerase = breads PDB in 1 strand, prevent supercoiling

Question 22

Describe DNA synth in the leading strand

Answer 22

RNA polymerase lays down primer, taken over by DNA polymerase

DNA polymerase synthesizes continuously

Question 23

Describe DNA synth in the lagging strand

Answer 23

RNA polymerase lays down primer, taken over by DNA polymerase

DNA polymerase synthesizes discontinuously until primer reached

Primer degraded by exonuclease

Gap filler by DNA polymerase

Adjacent Okazaki fragments joined by DNA ligase

Forms lagging strand loop

Question 24

Describe the end replication paradox found in the leading strand

Answer 24

Primer lost, small region not replicated

Loss of info prevented via telomeres

Question 25

Describe how telomerase acts

Answer 25

Template RNA on telomerase anneals to DNA of lagging strand

Telomerase adds bases

Telomerase translocates, maintaining base paring

DNA polymerase adds bases on leading strand side

Question 26

Describe how telomerase action differs between somatic and gametic cells

Answer 26

Somatic

• swicthed off => lose useful DNA in ageing
• primary tumors have active telomerase

Gametic
-active

Question 27

What are the types of mutations possible
What are the consequences of them
-point
-indels
-chromosomal

Answer 27

Point

• silent => same AA
• missense => diff AA
• nonsense => stop codon

Indels

• 3x => inframe
• not 3x => frame shift
• introns => :)
• exons => :(

Chromosomal

• inversion
• deletion
• duplication
• translocation

Question 28

What are the different causes of mutations and their consequences

• spontaneous
• induced (physical)
• induced (chemical)

Answer 28

Spontaneous

• DNA replication errors (poor proofreading/repair)
• Replication slippage (gain/loss of repeats)
• Deamination (C=>U)

Induced (physical)

• Ionisation => strand breaks
• UVB => thymine dimers

Induced (chemical)

• Nitrous acid (C=>U)
• Alkylation (G mod)
• Radicals (strand breaks

Question 29

Describe the process of DNA repair

• How frequently does repair happen
• In what cells does repair happen more frequently

Answer 29

Remove area around damage via nuclease, helicase

Resysnthesis via DNA polymerase

High fidelity of synthesis
-high replication rates => higher cancer risk in epithelial cells (intestinal carcinomas)

Question 30

Describe the relative nos of replication forks found between eukaryotes and prokaryotes

Answer 30

Prokaryotes
-1 origin => 2 forks

Eukaryotes
-many origins => many forks

Question 31

How would you access genetic info when the chromatin is highly condensed

Answer 31

Decondensed for transcription

• nucleosome sliding
• DNA pulls away from nucleosome

NEED ATP

Question 32

What 3 factors regulate expression of genes

What happens when regulation becomes faulty

Answer 32

Tissue specific expression
Ext signals change expression
Regulation in time and space (esp in development)

Cancer due to

• inappropriate cell div, angiogenesis
• inappropriate cell growth inhibition