Biol 253 Cell Cycle

Front 1

what is the first stage of mitosis?

Back 1

Prophase
Interphase is the resting phase between successive mitotic divisions of a cell, or between the first and second divisions of meiosis

Front 2

Explain Telophase

Back 2

The final phase of cell division, between anaphase and interphase, in which the chromatids or chromosomes move to opposite ends of the cell and two nuclei are formed.
Cytokinesis usually occurs at the same time that the nuclear envelope is reforming, yet they are distinct processes.

Front 3

Explain Prophase

Back 3

The first stage of cell division, before metaphase, during which the chromosomes become visible as paired chromatids and the nuclear envelope disappears

Front 4

Cell division in eukaryotes is more than just separating replicated
chromosomes (mitosis): Explain

Back 4

* mitosis and cytokinesis involve changes to membrane structure,
including breakdown and re-formation of the nuclear envelope.
* cytokinesis requires organelle replication and separation.
* mitosis requires replication of centrosomes (in animal cells).

Front 5

Three sub phases of Interphase?

Back 5

G1
S
G2
make up 90% of cell cycle

Front 6

Name the 3 cell cycle checkpoints

Back 6

i) G1 to S (is environment favorable?)
ii) G2 to M (Is all DNA replicated?)
ii) metaphase to anaphase. (Are all chromosomes attached to spindle?)

Front 7

genus for frogs?

Back 7

Xenopus
xeno=strange, pous=foot

Front 8

cdc?

Back 8

cell
division
cycle

Front 9

whats special about xenopus and sea urchin's cdc?

Back 9

G phase is skipped
synchronous

Front 10

cyclins?

Back 10

a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes
Made and destroyed during cell cycle

Front 11

MPF

Back 11

a heterodimeric protein composed of cyclin B and cyclin-dependent kinase (CDK1, also known as Cdc2 or p34 kinase) that stimulates the mitotic and meiotic cell cycles.

Observed in Xenopus to oscillate in parallel with cell cycle

Front 12

HeLa cells

Back 12

an immortal cell line used in scientific research
derived from cervical cancer cells taken on 1952 from Henrietta Lacks, a patient.

Front 13

Yeast

Back 13

Unicellular
Fungi

Front 14

budding yeast?

Back 14

S. cere visi ae

budding cerevisiae BC

Front 15

fission yeast?

Back 15

S. pombe

Fission Pombe FP

Front 16

whats different about budding yeast cdc?

Back 16

G2 phase skipped (S leads into M)
Daughter nuclei moves into bud formed

Front 17

Greatest advantage of studying yeast?

Back 17

Hapliod
usefull for isolating mutants as no second gene to screen for mutant.

Front 18

explain conditional mutants

Back 18

alternation between two conditional states, using a trigger. e.g. Temp
Permissive: Cell cycle progress' normally
Restrictive: cycle blocked at same stage
*** the mutant gene must act AT or BEFORE the stage where the cycle is blocked: Yeast used to identify proteins responsible for 3 cdc check points

Front 19

which cycling is in MPF?

Back 19

cyclin B
and Cdk

Front 20

CAKs?

Back 20

Cdk-activating kinases
fully activate Cdks after cyclins have partially activated
*** Adds a phosphate group to the T loop

Front 21

phosphate group?

Back 21

PO4 3−
transferred by Kinase

Front 22

Kinase

Back 22

phosphotransferase, is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates

Front 23

CKIs

Back 23

Cdk inhibitor proteins (Cki's)
block Cdk activity by preventing access to the active site of the Cdk.
Bind at or near active site
p27

Front 24

S cyclins are present until?

Back 24

S cyclins induce S phase and are present until mitosis
completely gone by the metaphase/anaphase transition

Front 25

M cyclins increase in concentration during..

Back 25

G2 phase
are lost during mitosis at the metaphase/anaphase transition

Front 26

two classes of cyclin required for G1 to S phase check point

Back 26

G1/S and S

Front 27

G1/S cyclins are present when?

Back 27

During G1

Front 28

which checkpoint is not cyclin dependant?

Back 28

metaphase to anaphase

Front 29

how many classes of cyclins are there in eukaryotes?

Back 29

four:
G1
G1/S
S
M (B cyclin and cdk 1)

Front 30

other names for cdk 1

Back 30

Cdc2 and Cdc28

Front 31

How was the human cdc2 (Cdk1 and cdc28) gene isolated?

Back 31

cDNA transferred to fission (pombe) yeast using plasmids.
Yeast were cdc2 mutants which grew long
Dividing colonies - short - were isolated

Human Cdk1 can function in yeast. This is why it was originally called Cdc2

Front 32

what is Wee1?
how does it function?

Back 32

a CKI (Cdk inhibitor)
deactivates cdk1 (cdc2 or 28) by phosphorylating it.
Regulates transition from G2 to M phase

DEACTIVATES

Front 33

What reactivates Cdk after Wee1

Back 33

cdc25 phosphatase

reactivation = earlier cell division

Front 34

what regulates Wee1

Back 34

Nim1/Cdr1
Cdr2

Front 35

when do G1 cyclins occur and what do they do?

Back 35

Occur only at the very start of the cell cycle in G1 phase
cause the activation of subsequent cyclins.
G1/S, S M cyclins

Front 36

what are mitogens?

Back 36

extracellular signals that trigger cell division
growth factors
used to regulate growth

Front 37

how do mitogens work

Back 37

signalling cascades: Reception-transmission-response
Receptor signals RAS which signals MAP kinase cascade
Gene expression produces Myc
up regulation of Myc transcription factor results in expression of G1 cyclins!!!

Front 38

what is a transcription factor?

Back 38

a protein that binds to specific DNA sequences, thereby controlling the flow (or transcription) of genetic information from DNA to mRNA

Front 39

explain the MAP kinase cascade

Back 39

a series of MAP Kinases are phosphorylated
amplifying a signal received at the plasma membrane
MAP Kinase phophorylates various proteins
result is either a change in protein activity or a change in gene expression

Front 40

what is a GTPase?

Back 40

hydrolase enzymes that can bind and hydrolyze guanosine triphosphate (GTP).

Front 41

what is RAS and what does it do?

Back 41

GTPase molecule
acts as a molecular switch inside the cell
active when bound to GTP

Front 42

name the molecules involved in RAS signalling

Back 42

GPP - a di phospate molecule (GDP)
GEF - removes GPP
GAP - hydrolyses phosphate on GPP (GTP becomes GDP) and RAS is turned off
GPP+P turns RAS on

Front 43

what do mitogens up-regulate

Back 43

Myc transcription factors

Front 44

what do G1 cyclins activate and how?

Back 44

Activate E2F protein
by phosphorylation

Front 45

how do G1 cyclins allow S phase gene expression

Back 45

activates E2F protein which phosphorylaes Rb protein, rendering it inactive.
Rb= retinoblastoma

Front 46

proteins that deactivate Rb....?
name one

Back 46

allow the cell cycle to occur by activating E2F
G1 cyclin

Front 47

how does the cell cycle continue once Rb is deactivated?

Back 47

an activated E2F protein drives TRANSCRIPTION of G1/S and S cyclins, and of itself (E2F via +ve feedback loop)

Front 48

3 ways E2F is activated?

Back 48

G1 cyclin deactivates Rb (retinoblastoma)
E2F activates transcription of itself ( +ve feedback loop)
G1/S and S cyclins activate E2F ( +ve feedback loop)

Front 49

what are telomeres

Back 49

a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes

Front 50

what does telomerase do?

Back 50

is an enzyme
that adds DNA sequence repeats ("TTAGGG" )
to the 3' end of DNA strands in the telomere regions
which are found at the ends of eukaryotic chromosomes

Front 51

where does DNA replication begin?

Back 51

at multiple points on each chromosome called REPLICATING ORIGINS

Front 52

How do cells prevent re-initiation of of DNA synthesis? S phase?

Back 52

Cycling of APC/C, S- and M-Cdk

1) Chromosome replication requires the pre-replication complex (pre-RC). This is formed by the APC/C during G1.
2) S-cyclin disassembles the pre-replicative complex ( cdc6 and mcm proteins) when it triggers DNA synthesis.
3) broken down.

Front 53

Explain the initiation of DNA replication

Back 53

At the start of G1 phase, the APC/C complex initiates pre-replication complexes....
1-Protein Complex ORC (origin recognition complex) binds to replication origins
2-cdc6 and Mcm form the pre-replication complex (pre-RC)

Front 54

Explain DNA synthesis

Back 54

S-cyclins cause initiation of DNA synthesis during S phase
1-S-cyclin triggers the release of cdc6 via phosphorylation (followed by degradation)
2- Pre-initiation complex phosphorylates ORC forming the initiation complex
3- Replication complex replicates DNA

Front 55

what is endomitosis and endoreduplication and when is it used?

Back 55

S phase, without Mitosis, causing polyploidy
checkpoint that usually prevents DNA synthesis without mitosis is "over-ridden"
very common amount plants
Megakaryocytes: a bone marrow cell responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting.

Front 56

Ubiquitin?

Back 56

Ubiquitin is a small regulatory protein that has been found in almost all tissues (ubiquitously) of eukaryotic organisms. Among other functions, it directs protein recycling

Front 57

The DNA Damage checkpoint - general

Back 57

An activation pathway triggers protein phosphorylation causing gene transcription of a CKI

Front 58

The DNA Damage checkpoint - detailed

Back 58

chk1/chk2 kinase activation
p53 phosphorylation and DEactivation
cdc25 reverses the deactivating effect of the Wee1 kinase on Cdk-cyclin
p53 binds to p21 gene which encodes a CKI (Cdk inhibitor protein) causing the expression of CKI
CKI blocks cell division by blocking cyclin

Front 59

Give details of Centrosome replication

Back 59

During G1 the CENTRIOLES split
During S phase each replicates forming two centrosomes
each centrosome is semi-conserved
***controlled by cyclins!

Front 60

what do centrosomes do?

Back 60

they nucleate MT's allowing for chromosome separation

Front 61

sister chromatids are held together by what?

Back 61

Cohesion protein

Front 62

what and where are the 3 cell cycle checkpoints?

Back 62

1- G1 (Restriction) Checkpoint is located at the end of the cell cycle's G1 phase, just before entry into S phase.
2- G2 Checkpoint is located at the end of G2 phase, triggering the start of the M phase (mitosis)
3- Metaphase Checkpoint occurs at the point in metaphase where all the chromosomes have aligned at the mitotic plate

Front 63

Damage of p53 causes what?

Back 63

loss of control over the cell cycle
***allowing DAMAGED DNA to be replicated - cancer yo!

Front 64

what is responsible for the onset of mitosis?

Back 64

Activating M cyclins during G2

Front 65

name the three checkpoints

Back 65

G1 to S (two classes of cyclins required)(proceed to S phase)
G2 to M (proceed to M phase)
Metaphase to anaphase (proceed to separate chromosomes)

Front 66

what partially and fully activates Cdk?

Back 66

Cyclin = partially
CAK = fully (Cdk activating Kinase)

Front 67

what prevents M cyclin from activating Mitosis too early?

Back 67

CKI's
block Cdk activity by preventing access to the active site of the Cdk
what CKI?

Hint 67

Wee 1 of course

Front 68

mitosis results from the action of what phosphatase?

Back 68

cdc25 (Reactivates M-Cdk)
is there feedback loop?

Hint 68

yes, +ve
M-Cdk further activated Cdc25

Front 69

deficient Cdc25 or excess Wee 1 causes what?

Back 69

Elongated cells.
Why?

Hint 69

Increase in G2 and delayed division

Front 70

When does chromatin condense?

Back 70

During cell division - Mitosis

Front 71

At the end of S phase the sister proteins are held together by a protein called?

Back 71

Cohesin

not cohesion

Front 72

Cohesin is partly removed when?

Back 72

During chromatin condensation
yes but when is that?

Hint 72

during Prophase

Front 73

when is cohesin added?

Back 73

G1 phase
before replication

Front 74

what protein regulates condensation?

Back 74

Condensin
but how is it activated?

Hint 74

phosphorylation by M-Cdk
Condensin 2

Front 75

Name the Intermediary Filament that give internal support to the nucleus

Back 75

Lamins
provide structural support

Front 76

where does the nuclear envelope go during cell division?

Back 76

it collapses back into the ER

Front 77

what trigger the nuclear envelope breakdown?

Back 77

Phosphorylation of Lamins by the M-Cdk.
Makes them soluble so the no longer provide support to the membrane.

Ah but what triggers it to reform?

Hint 77

DEphosphorylation of lamins.
When the M-Cdk are no longer active.

Front 78

Name the three arrays of MT spindle

Back 78

Astral - like the stars
Kinetochore
Interpolar - join to other sides MT's

Front 79

5 processes stimulated by M cyclin phosphorlation

Back 79

1- chromosome condensation
2- nuclear envelope breakdown (and reformation)
3- assembly of MT spindle
4- increased MT dynamics by modulating MAPs
5- reorganisation of the cytoplasim

Front 80

3 processes triggered by the APC/C complex?

Back 80

Chromosome separation
breakdown of S and M cyclins
formation of the prereplicative complex at origins of replication

Front 81

what is the only stable kinetochore configuration?

Back 81

Kinetochore on each chromaTID to be attached to OPPOSITE spindle poles

Front 82

an improperly attached chromosome associates with which protein?

Back 82

Mad2

Front 83

what does APC/C stand for?

Back 83

Anaphase PROMOTING complex/ CYCLOSOME.
which checkpoint?

Hint 83

Metaphase anaphase

Front 84

how does the APC/C work? Basic

Back 84

protein destruction. Targets...
1- S and M cyclins
2- Securin

also initiates REPLICATIVE COMPLEXES for DNA replication

Front 85

how does APC/C work? Detail

Back 85

protein degradation through polyubiquitination
chain of Ubiquitin added to protein, targets it for detruction

what destroys it?

Hint 85

Proteasome does

Front 86

what activates the APC/C complex?

Back 86

Cdc20

Front 87

how does cohesion get broken down?

Back 87

cdc20 binds and activates APC/C
APC/C ubiquinates SECURIN which releases SEPARASE.
Separase cleaves Cohesin, releasing the sister chromotids

Front 88

targeted destruction of what allows formation of the prereplicative complex?

Back 88

Cyclins

Front 89

How does APC/C get deactivated?

Back 89

M-Cdk activates APC/C
APC/C destroys cyclins which detroys M-Cdk.

Author of its own demise!
Designed obsolescence

Front 90

If APC/C destroys cyclins, how does the cell cycle restart?

Back 90

G1 cyclins do not suffer from APC/C targeting. Bam!

But how do G1 cyclins come about?

Hint 90

Mitogens yo!

Remember G1 stimulate the other cyclins, G1/S and S. Boosh!