DNA replication and the cell cycle Flashcards Preview

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Flashcards in DNA replication and the cell cycle Deck (48):
1

telomere

highly repetitive DNA that allows the end of the chromosome to be replicated- also protects it from degradation

2

centromeres

repetitive dna which forms the spindle attachment site in mitosis

3

origin of replication

special sequence where duplication of DNA begins; each chromosome will have many origins

4

features of the chromosome that reflects their need to replicate and partition

telomere
centromere
origin of replication

5

DNA pol
vs
RNA pol

-dna polymerase is far more accurate - due to it having a longer lifespan
-DNA polymerase has a proof reading mechanism- it can detect if it has incorporated the wrong base--> CAN GO BACK AND REMOVE FALSE NUCLEOTIDES AND THIS IS DONE BY EXONUCLEASE

6

does RNA polymerase have a proof reading mechanism

no

7

evidence of semi conservative dna: Meselson and Stahl

- they proved this by growing bacteria for many generation in DNA that contained a heavy isotope of nitrogen called N15- which became incorporated in the DNA- DNA became more dense
-they then grew it for a number of generations in normal nitrogen
-all dna became less dense
-proved half dna was conserved

8

what is needed for dna syntehsis

DNA polymerase and Mg2+
dNTPs (deoxynucleotides)
single stranded template of DNA
-primers 3" OH group- short single strand of DNA with a hydroxyl group

9

dna synthesis occurs

5' to 3' because DNA polymerase acts on the 3'-OH of the existing strand for adding free nucleotides

10

what provides energy for polymerisation

when nucleotide joins the growing DNA polynucleotide- 2 phosphates are lost--> leaving one to join

11

complementary base pairs are joined via

h bonds between single stranded dna

12

dna polymerase requires

a primer with a 3'OH residue to extend from

13

bacterial genomes are..

small, compact, circular
-no histones
-associated with Mg2+ and polyamides

14

eukaryotic genomes

large
arranged as a liner chromosomes
histones

15

what determines the speed of replication

sliding clamp- around 50bp per s in eukaryotes. In bacteria around 1000bps

16

what loads the sliding clamp on the DNA

clamp loader
-sliding clamp encircles the double stranded dna and ensures high productivity

17

enzymes at the replication fork

helicase
ss binding protein
primate
DNA polymerase
sliding clamp
nucleases
dna ligase

18

helicase

unwinds double stranded DNA

19

ss binding protein

stabilises ssDNA

20

primase

synthesises RNA primer

21

dna polymerase

synthesis of new dna strand

22

dna polymerase

proof read

23

siding clamp

keep dna polymerase on DNA

24

nucleases

trim the okazaki fragments

25

dna ligase

join okazaki fragments

26

okazaki fragments

Okazaki fragments are short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication. They are complementary to the lagging template strand, together forming short double-stranded DNA sections

27

single stranded binding proteins

prevents base-pairing until DNA polymerase arrives- however does mot mask the nucleotide -- otherwise single stranded dna may base pair with itself and become folded

28

which protein detects incorrect base pairing in newly synthesises DNA

mismatch repair protein MutS- detects incorrect base pairing in newly synthesised DNA

29

mismatch protein mechanisms

erro in newly made strand
-mistmatch proofreading proteins attach-nut s to strand and MutL to the Mut S.
-dna is scanned and detects nick in new dna
-this area is removed
-this area becomes single stranded and the correct nucleotides will join
-repaired dna

30

DNA synthesis is ...

bidirectional from sites of origin- there may be a number of sites of origin--> forms replication bubbles

31

what forms replication bubbles

the bidirectional nature of dna synthesis

32

s phase

dna replication

33

m phase

mitosis

34

G1 and G2

where checking mechanism occur and events that occur between replication and division

35

where is the site of dna replication

replication fork

36

events at replication fork

-both strands copied at replication fork
-5' to 3'
-leading strand will have continuous synthesis (only needs to be initiated one)
-lagging strand will have discontinuous synthesis (multiple rounds of initiation and synthesis

37

leading strand

continous synthesis- only needs to be initiated once

38

lagging strand

discontinue synthesis- multiple rounds f imitation and synthesis

39

however bacterial dna has...

one origin of replication

40

what loads histones onto newly synthesised DNA

histone chaperons --> to condense the new dna into chromosomes

41

helcase unwinding of dna causes

supercoiling ahead of the replication fork which needs to be unwound by TOPOISOMERASE- by breaking and reforming phosphodiester bonds

42

which enzymes undoes supercoiling before the replication fork

topoisomerase- breaking and reforming phosphodiester bonds

43

why do leading and algid strand occur

due to the antiparallel nature of dna--> synthesis is occurring in the opposite direction on each stand. Lagging strand is more complicated because it is synthesises 3' to 5' meaning a diff type of dna polymerase is used

44

why is lagging strand more complicated

synthesised from 3' to 5'- meaning a diff dna polymerase is used

45

what is the lagging strand also referred to

OKAZAKI FRAGMENTS

46

synthesis of the lagging strand

1. primase synthesises short RNA oligonucleotides (primers) copied from dna
2. dna polymerase elongates RNA primers with new dna
3. nucleases remove RNA at 5' end of the neighbouring fragment and dna polymerase fills in the gap
4. dna ligase connects adjacent okazaki fragments

47

how many basepairs per second in bacteria

1000bps

48

how many BP per second in eukaryotes

50bps