Unit 12- DNA Replication

Question 1

types of replication

Answer 1

• conservative replication
• dispersive replication
• semiconservative replication

Question 2

Mesel’s and Stahl’s experiment

Answer 2

2 isotopes of nitrogen
- 14N common form; 15N rare, heavy form
- E coli were grown in 15N then to 14N media
- grown E.coli were centrifuged (density gradient)

Question 3

replicons

Answer 3

units of replication (how long from 1 origin of replication)

Question 4

theta replication

Answer 4

circular DNA, E. Coli; single origin of replication forming a replication fork, and it is usually bidirectional replication

Question 5

rolling-circle replication

Answer 5

virus, F factor of E.Coli; single origin of replication (cut one side DNA and synthesize, pealing off strand. peeled off strand loops and is copied)

Question 6

linear eukaryotic replication

Answer 6

• eukaryotic cells
• thousands of origins
• a typical replicon: ~200000-300000 bp

Question 7

requirements of eukaryotic replication

Answer 7

• a template strand
• raw material: nucleotides (dNTPs)
• enzymes and other proteins

Question 8

Direction of replication

Answer 8

• DNA polymerase adds nucleotides only to the 3’ end of growing strand
• replication can only go from 5’ to 3’
  (5’ end: phosphate side
  3’ end: OH end)
• continuous and discontinuous replication

Question 9

leading strand

Answer 9

undergoes cont replication

Question 10

lagging strand

Answer 10

undergoes discontinuous replication

Question 11

okazaki fragments

Answer 11

discontinuously synthesized short DNA fragments forming the lagging strand

Question 12

indicator protein

Answer 12

binds to origin and seperates strands of DNA to initiate replication

Question 13

DNA helicase

Answer 13

unwinds DNA at replication fork

Question 14

single-stranded-binding proteins (SSBPs)

Answer 14

attach to sing-stranded DNA and prevent secondary structures from forming

Question 15

DNA gyrase (toperasomerase)

Answer 15

moves ahead of replication fork, making and resealing breaks in the double -helical DNA to RELEASE the TORQUE that builds up as a result of unwinding

Question 16

DNA primase

Answer 16

synthesizes a short RNA PRIMER to provide a 3’-OH group for the attachment of DNA nuclotides (* multiple for lagging)

Question 17

DNA polymerase III

Answer 17

elongates a new nucleotide strand from the 3’ (moves 3’ to 5’)(new DNA in the 5’ to 3’ direction)

Question 18

DNA polymerase I

Answer 18

removes RNA primers and replaces them with DNA

Question 19

DNA ligase

Answer 19

joins okazaki fragments by sealing breaks in sugar-phosphate backbone

Question 20

*Heteroplasmy

Answer 20

when a cell has mitochondria/chloroplast that have different genes in each

Question 21

origin-recognition complex (ORC)

Answer 21

binds to replication start site to initiate DNA replication
- recruits and loads helicase
- not needed in Eukaryotes

Question 22

DNA polymerase delta

Answer 22

lagging-strand synthesis, DNA repair, translesion DNA synthesis

Question 23

DNA polymerase epsilon

Answer 23

leading-strand synthesis

Question 24

end-replication problem

Answer 24

end cant be synthesized on lagging strand as Primase doesn’t have enough space to bind and replicate ending

Question 25

telomerase

Answer 25

complement RNA template that attaches to end and overhangs. New DNA is build off overhang. Enough space for Primase to synthesize.