DNA replication and cell cycle

Question 1

cell cycle phases

Answer 1

g1
g2
m
s

Question 2

S phase processes

Answer 2

Unfold chromatin structure
copy DNA completely and accurately
Refold DNA back into chromatin

Question 3

DNA replication elongation

Answer 3

how the replication fork moves through a region of DNA
is in semi discontinuous fashion
leading and lagging strands

bi directional

Question 4

Proteins active at replication fork

Answer 4

helixcase to open dna strand
polymerase / pcna and rpa for leading strand

polymerase
primase
pcna
dna ligase
etc for lagging strand

Question 5

Helicase

Answer 5

unwinds the dna strand
made up of 6 proteins called mcm
complexed with cdc45 and GINS complex - CMG
Specific regions of genome may have their own helicases

ws for ribosomal repeates

Question 6

Leading strand factors

Answer 6

polymerase - synthesises DNA
Rpa- single stranded binding protein - protects it
Pcna - processivity factor for the polymerase - keeps polymerase associated to dna

Question 7

Lagging strand factors

Answer 7

Okasaki fragment initiation by DNA polymerase alpha
Primase - synthesis of RNA primer
Polymerase- DNA synthesis

Question 8

lagging strand factors 2

Answer 8

polymerase alpha starts of process then polymerase switching occurs.

Question 9

lagging strand factors 3

Answer 9

joining of okasaki fragments by rnaseh, fen1 and dna2
rfc,pcna,polymerase
and with DNA ligase it all becomes connected

Question 10

Initation of replication

Answer 10

DNA component- origin of replication
protein components - the machinery of initiation

Question 11

origin of replication

Answer 11

ARS - autonomously replicating sequences

Question 12

Initation proteins

Answer 12

ORC - origin recognition complex
Cdc6
Cdt1
MCM complex

Question 13

The initation pathway

Answer 13

ORC binds to DNA
recruites CDT1 and CDC6
CDT1 loads MCM proteins onto chromatin - preRC complexs formed

other proteins then joined and pre initiation complex formed
then elongation

Question 14

Termination

Answer 14

replication forks stop when they hit each other.

Question 15

Replication fork barriers

Answer 15

Termination sites where forks stop

Question 16

general points

Answer 16

all origins do not fire at same time
genome is divided into early and late replicatin regions

early - euchromatin

late - silent and heterochromatin

Question 17

Replication occurs in replication factories

Answer 17

enzymes are held onto frame works
points of replication seem to be cluseted into 300 sites - multiple forks at each site called rep factories

Question 18

Linear chromosomes habe specialised end

Answer 18

causes shortening of chromosomes
telomeres are at end
replicated by telomerase that add extra repeates at end

Question 19

mechanics of mitosis

Answer 19

prophase - chromosome condensation
metaphase - chromosome congression
anaphase ab- sisterchromatid seperation and cleavage furrow formation

telophase - dna seperates into two different nuclei

Question 20

chromosome condensation

Answer 20

dna is compressed to make it shorter and fatter.
main protein in this is condensin - structure two globular hand and hinge to attach to dna and flex.
condensin may form rings around chromatin
either by random or similar to cohesin action

Question 21

metaphase structures

Answer 21

kinetochore
spindle
spindle pole bodies

Question 22

the kinetochore

Answer 22

region on chromosome attached to spindle
complex structure - multiple regions
DNA - centromeric heterochromatin - very repetitive

proteins - many types, structural, sequence specific and molecular motors

Question 23

the spindle and spindle pole bodies

Answer 23

pole bodies - two tubues of tubulin at right angles to each other surrouned by pericentriole material where microtubules are ennucleated

spindle - microtubulin made of a and b tublin and has plus/minus end. has directionality

Question 24

spindle dynamic

Answer 24

spindle pole duplicates to give two.
new ones moive to edge assisted by motors
spindle generated
invades region of chromosomes and looks for kentichore.
microtubules sento to cytoplasm to anchor

Question 25

Anaphase

Answer 25

chromosome pulled toward poles by molecular motors and microtubule shortening a- toward poles b- poles move apart

Question 26

telophase

Answer 26

two new nuclei form and the chromosomes decondense next cytokinesis

Question 27

systems help in understand mitosis

Answer 27

biochem and genetics in yeast - condensation and kinetochore structure spindle stuff - biochem on xenopus invitro extracts

Question 28

control of cell cycle

Answer 28

phosphorylation and cdks

Question 29

identification of cdks

Answer 29

yeast cell division mutants xenopus oocytes and eggs

Question 30

cdk kinases

Answer 30

2 sub units kinase subunit cyclin subunit-controller and determines specificity

Question 31

cyclin cdk complexes

Answer 31

redundacies in cyclin so we can llose some types and still allows for cell sruvival

Question 32

what do cdks do

Answer 32

phosphorylate key groups of proteins - changes activity state of proteins and drives cell into next phase of cell cycle e.g. replication initation protein some proteins repressed or activated cdks can have diff effects on same proteins modiifcation not permenant cdk needed to be present to sustain

Question 33

cell cycle characterised ?

Answer 33

by cyclin activity one cdk can modify next cdk to be active / next cdk can decrease the cdk before it

Question 34

how is cyclin cdk activity is controlled ?

Answer 34

by transcription , proteolysis - act on clclin not cdk modification, inhibition, cell localisation - act on cdk/cyclin complex

Question 35

cyclin transcriptional control

Answer 35

growth factors - activate transcription factors - activation of cyclin genes or activation of other cell cycle controlled proteins

Question 36

proteolysis of cyclin

Answer 36

negative effect at g2 to m phase transition cyclin b is broken down by first being modified by ubiquitin chain then proteosome breaks it down

Question 37

modification of cdk/cyclins

Answer 37

positive or negative negative - wee1 kinase for cdc2 inactivation positive - cdc25 phosphotase - activates cdc2

Question 38

cdk inhibitors

Answer 38

sic, rum sp p21 - cdk 1/2 p28 - cdk 1/2/4/5

Question 39

variation to basic cycle 1

Answer 39

meiosis 2 rounds of nucler division

Question 40

polymitosis

Answer 40

cell carries out multiple rounds of mitosis with no intervening dna replication happens in polyploid tissue

Question 41

polyploidisation

Answer 41

mutliple rounds of replication with no intervening mitosis form clumps of dna or polytenisation

Question 42

amplification

Answer 42

multiple initations causes a nested structure extra dna added to dna through recombination