The molecular cell cycle

Question 1

The cell cycle – why yeast?

Answer 1

Easy for us to see under a microscope + loads of visible replications

Question 2

How can we identify and see each stage?

Answer 2

Process by which single eukaryote gives rise to two identical daughter cells.Most cells have a finite capacity for division and can be senescent at anytime- scenesent -process by which the cells irreversibly stop dividing and enter a state of permenant growth arrest without undergoing cell death.Senescent cells sit within the tissue and can change the plasticity of the tissue, the longer they sit around can be promoting a cancer

Question 3

What gene group is responsible?

Answer 3

E2F is a group of genes that encodes a family of transcription factors(TF) in higher eukaryotes

Question 4

What are the events of the cell cycle?

Answer 4

Interphase,G1,S,G2 and Mitotic Phase.

Question 5

What happens at g1?

Answer 5

Part of interphase – during the first gap – the cells grow physically larger, copies organelles and makes the molecular building blocks it will need in later steps, the availability of growth factors will control the animal cell cycle at a point in late g1 phase, called the restriction point; if growth factors are not available during g1, the cells enter a quiescent stage of the cell cycle called g0.

Question 6

What happens at S?

Answer 6

also part of interphase, the cell synthesises complete copy of DNA in its nucleus- also duplicates a microtubule structure calles the centromere- the centromere help sepearte dna during the M phase.

Question 7

What happens at G2

Answer 7

During the second gap phase, the cell grows more – makes proteins and organelles and begins to reorganise its content in preparation for mitosis . G2 ends as mitosis begins.

Question 8

What happens at the mitotic phase?

Answer 8

The cell divides its copied DNA nd cytoplasm to make 2 new cells.Mphase involves 2 distinct division- related processes.
Mitosis and cytokinesis
In the prophase of mitosis, chromosomal Material condenses to form compact mitotic chromosomes.The cytoskeleton is disassembles and mitotic spindle is assembled.
In the prometaphase, the chromosmomal microtububles attach to kinetochores of chromosomes and are moved to spindle equator.
In metaphase- chromosomes are aligned along the metaphase plate and are attached to both poles by microtubules
In anaphase- the centromeres split and chromatids separate moving the chromosomes to opposite single poles.
In telophase, the chromosomes cluster at opposite poles.The nuclear membrane assembles around the cluster which daughter cells formed by cytokinesis.

Question 9

What are the 4 nucleotides?

Answer 9

Adenine Guanine, Thymine, cytosine

Question 10

What Is non mutagenic replication?

Answer 10

Non muatnigenic replication of every
nucleotide is essential once per cycle, only one copy should be made and no
muations!

Question 11

Which nucleotides are pyrimidines?

Answer 11

Thymine and cytosine

Question 12

Which nucleotides are purines?

Answer 12

Adenine and guanine

Question 13

Why do we incorporate radiolabelled nucleotides?

Answer 13

3h-thymidine) are in cooperated
into cells at DNA replication. Using X ray or antibody staining, cells in S- phase may be identified. Flow cytometric detection of cells stained with DNA dyes allows the discrimination of cells with variable DNA content. Cells in G1 phase – peak 1 contain half the DNA of cells after DNA replication in G2 and M(peak 2), cells in the process of replication (S- Phase) contain an intermediate quantity.

Question 14

What is the role of Cyclins and what do CDKs stand for?

Answer 14

In order to drive the cell cycle forward. Cyclin dependant kinases. A cycline must activate or inactivate target proteins inside the cell.- cyclins drive the event of a cell cycle by partnering with a family of enzymes called cdks. A lone cdk is inactive but when a cyclin is involved it becomes activated -making it a functional enzyme and allowing it to modify target proteins.

Question 15

What is the cdk required for a cell cycle to take place and what is the name of an important example of one of them?

Answer 15

Cdk 1 is required to drive through the cell stages.Cyclin B1 and A2 are essential for a normal cell cycle

Question 16

Which cdks act on which part of the cycle

Answer 16

At G1 phase – CDK 4 and CDK 6 binds to cyclin D- Cyclin d levels are influenced by extracellular signals(mitogens,growth factors and survival factors)- The main target of cdk 4 and 6 is retinoblastoma protein RB,dysfunction of Rb(stuck in on position)may lead to uncontrolled proliferation,where mutations are likely. G1/S phase – CDK 2 binds to Cyclin E, S - phase – CDK2 binds to cyclin A,M/G2 phase:CDK1 (aka cdc25) binds to cyclin B1

Question 17

Give the two examples of cdk inhibitors

Answer 17

proteins that bind to CDK cyclin complexes
and completely block their activity, Wee1 kinase inhibits phosphorylation of threonine 14 and tyrosine 15 on CKD1, inhibiting cell cycle progression Cdk1 phosphatase reverses the change of Wee1, leading to active CDK

Question 18

How are cdks acativated?

Answer 18

CDKS are activated by activating the phosphorylation of threonine around position 160.

Question 19

How do cell cycle check points navigate the cell cycle?

Answer 19

The availability of cyclins controls the activity of CDKs and promotes cell progression.CDKs become active via cyclin- binding – when complexed with M -phase cyclin, mitosis machinery is triggered, when complexed with s- phase cyclin DNA replication Machinery is triggered.

Question 20

What happens at the G1 checkpoint of the cell cycle?

Answer 20

Cell size,growth factors and dna damage are checked.If the cell doesn’t meet requirements- it will leave the cell cycle and enter g0 – resting state.

Question 21

How does p53 effect this?

Answer 21

Dna damage causes p53 levels to rise,causing transcription of p21, p21 binds to PNCA – a component of dna replication machinery – preventing its activity. By ensuring that cells don’t divide when their dna is damaged, p53 prevents mutations when p53 is defective or missing,mustations can accumulate quickly,potentially leading to cancer.Out of all the human genome p53 is the most mutated and often mutated in cancers

Question 22

What happens at the G2 phase of the cell cycle?

Answer 22

Unreplicated or damaged DNA are checked, if errors found the cell will pause for repairs.Topoisomerase 2 is responsible for repairing dna at this stage.If the checkpoint mechanisms detect a problem with DNA, cell cycle is halted and the cell attempts to either complete dna replication or repair the damaged DNA. If damage is irrepairable,the cell may undergo apoptosisor programmed cell death

Question 23

How does this affect cdc25? g2

Answer 23

A signal is sent to a series of protein kinases which phosphorylate and inactivate cdc25.This de-phosphorylation of M-CDK is blocked and it does not activate, preventing entry into mitotic phase

Question 24

What happens at the Mphase of the cell cycle?

Answer 24

aka spindle checkpoint – chromosomal misalignment(ie.chromosme not attached to the spindle)will stop the cycle.If a chromosome is misplaced,the cell wall will pause mitosis allowing time for the spindle to capture the stray chromosome

Question 25

What is the restriction point?

Answer 25

If no gf -cell goes into g0

Question 26

What is PI3K signalling a form of?

Answer 26

endocrine signalling

Question 26

At what stages can the cycle be stopped?

Answer 26

G1,M,G2

Question 27

Where does it work and what does it act on?

Answer 27

The pituitary gland releases a growth hormone which acts on tyrosine kinase receptors.

Question 28

What is a kinase?

Answer 28

An enzyme that transfers phosphate group to a protein or other target and a receptor tyrosine kinase transfers phosphate groups specifically to amino acid tyrosine,activating it

Question 29

-

Answer 29

-

Question 30

What is HER 2 signalling and where does it work and what does it affect specifically?

Answer 30

Member of the human epidermal growth factor,HER EGFR ERBB family.The her 2 receptor is a transmentrane tyrosine kinase receptor that consists of extracellular lignands binding domain,a transmembrane region and an intracellular or cytoplasmic tyrosine kinase domain.

Question 31

What does it activate? HER 2 signalling

Answer 31

It is activated by the formation of homodimers or heterodimers with other epidermal growth factors (egfr) proteins.Further downstream molecular signalling cascades are activated, such as ras/raf/mitogen activated protein kinase MAPK,the phosphoinositide 3-kinase/Akt and the phospholipase cy(PLCy)/protein kinase C (PKC) pathways that promote cell growth and survival and cell cycle progression

Question 32

What is the MAPK pathway?

Answer 32

When growth factor ligands bind to their receptors, the receptors pair up and act as kinases.The activated receptors trigger a series of events. Ras is activated- KRAS (K-ras and ki- ras) is a gene that acts an on/off switch in cell signalling.When it functions normally,it controls cell proliferation.when it is mutated,negative signalling is disrupted.Guanine nucleotide exchange factors GEFs are recuited.GEF becomes capable of interacting with Ras proteins at the cell membrane to promote a conformational change and the exchange of GDP for GTP.Raf is recruited to the cell membrane and activation stimulates a signalling cascade by phosphorylation of MAPK which successively phosphorylate and activate downstream proteins such as ERK1 and ERK2. Transcription factors are activated promoting cell growth and division

Question 33

What is an oncogene and how can that affect the progression of breast cancer.

Answer 33

Over expression of this oncogene has been show to play an important role in the development and progression of certain aggressive typesof breast cancer.The protein has become an biomarker and target of therapy for approx. 30% of BRCA pts,Her 2 positive brca are activated by promoting cell growth and division