DNA-replikasjon, kromosomer Flashcards

1
Q

Hvor lang tid tar det for en mammalsk celle å gjennomføre en komplett cellesyklus?

A

En gjennomsnittlig animalsk celle gjennomfører en komplett cellesyklus i løpet av ca 24 t, og de ulike fasene er som følger:

  • G1: 12 t
  • S: 6 t
  • G2: 6 t
  • M: 30 min
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2
Q

Hva er kromosomer?

A
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3
Q

Hva må skje med kromosomene før celledelingen?

A
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4
Q

Hvilke ulike former for DNA-replikasjon har man?

A
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5
Q

Hva er DNA-et sitt rolle ved cellereplikasjon?

A

Det er enorme mengder DNA som må replikeres i kroppen.

Hvis en antar at antall celler i kroppen ligger opp mot 10^13, og at lengden på DNAet i hver celle er ca 1.5m, vil vi ha > 10^13 m DNA i kroppen.

Dette tilsvarer mer enn 1010 km, som er nesten 100 x mer enn avstanden til solen.

I løpet av et helt liv vil alle cellene i kroppen være skiftet ut mange ganger, så lengden på DNAet dannet vil være astronomisk.

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6
Q

Hva viste Meselson og Stahl når det kom til DNA-replikasjon?

A

Semiconservative was not the only model of DNA replication.
Other proposed models included conservative replication and dispersive replication.

Conservative replication proposed that after replication, one DNA molecule consists entirely of newly synthesized DNA whereas the other molecule is entirely original DNA.

Dispersive replication suggested that each DNA molecule after replication might consist of segments of new and old DNA interspersed.

It would be difficult to devise a mechanism by which this latter outcome might occur, but until evidence to the contrary was produced, it had to be considered.

To distinguish between these possibilities, Meselson and Stahl did the following experiment:

First, they grew bacteria for many generations in a growth medium containing 15N. This is a heavy isotope of nitrogen (in contrast to the normal isotope, 14 N), which over many generations would be incorporated into all nitrogen-containing molecules of the cells, including DNA.

DNA isolated from these cells could be distinguished from normal DNA because it would have a higher density.

The bacteria grown in heavy nitrogen were then transferred to growth medium containing 14 N for one round of replication.

This lighter isotope would incorporate into any newly synthesized DNA. If semiconservative replication occurred, then each DNA molecule after replication would contain heavy nitrogen and light nitrogen, and would therefore have a density intermediate between the two.

Conservative replication would produce one DNA molecule containing heavy nitrogen and one molecule containing light nitrogen, so there would be two different densities.

Dispersive replication would
produce a single intermediate density, just like semiconservative.

I E. coli celler tar det ca 42 minutter å replikere hele kromosomet på 4.6 mill basepar; det vil si at det dannes ca 1000 basepar pr sek.

Hos mennesket går denne prosessen mye langsommere, og det dannes ca 100 bp pr sek.

Hele det humane genom på 3 x 10^9 bp trenger ca 8 t på å kopieres, noe som betyr at det må dannes minst 1000 replikasjons”bobler” i det humane genomet.

Elektronmikroskopiske analyser av replikerende DNA, har imidlertid vist at antallet ligger mellom 10 000 og 100 000

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7
Q

I hvilken retningen skjer kromosomal DNA replikasjon?

A
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8
Q

Hvor starter DNA replikasjonen?

A

“Smelteforsøkene” ble verifisert etter oppdagelsen av restriksjonsenzymene.

Ved å behandle virus-DNAet med et enzym som kutter på en bestemt plass, fant en at replikasjonen alltid startet på et punkt med samme avstand til kuttstedet.

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9
Q

Hvordan initiseres en DNA replikasjon?

A

Initiation begins at a single site, oriC, with a complex of proteins and a primer mRNA:

  • The oriC gene in E. coli has 4 sites with the consensus sequence; TTAT(C/A)CA(C/A)A, which binds DnaA.
  • 20-40 monomers of DnaA.ATP bind to oriC as a first step to initiation of DNA replication (only this active form allows in vitro initiation)
  • Immediately following replication, the DNA is in a hemimethylated state, and oriC binds to the cell membrane for 8-10 minutes.

DnaA:

  • DnaA is a stable protein that has several forms: Unbound, bound to either ATP or ADP, bound to cardiolipin, and bound to the chromosome
  • The dnaA gene is autoregulated and located near oriC
  • DnaA appears to not binds hemimethylated DNA

Elongation and the C Period:

  • Replication of the DNA proceeds in a bidirectional manner with another set of proteins
  • The C Period is roughly constant at about 45 minutes for many growth conditions
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10
Q

I hvilken retning skjer DNA-syntesen?

A
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11
Q

Hvilket protein er viktig for dannelsen av nytt DNA?

A
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12
Q

Hva er det som sikrer at rett nukleotid blir satt inn?

DNA-replikasjon

A
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13
Q

Hva skiller de ulike DNA polymerasene fra hverandre?

A
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14
Q

Hva mener man med av DNA-replikasjonen er semikontinuerlig?

A
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15
Q

Hva er topoisomerase?

A
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16
Q

Hva danner “lagging strand” under DNA-replikasjonen?

Orientering i samme retning

A
17
Q

Hva skiller eukaryot DNA-replikasjon fra prokaryot?

A
18
Q

Hvordan foregår prosesseringen av Okazaki-fragmentene?

A
19
Q

Hva skjer ved enden av kromosomene?

A
20
Q

Hvilke mekanismer sørger for korrekt DNA-replikasjon?

A
21
Q

Hvordan er den overordnete kontrollen av DNA-replikasjonen?

A