CANCER 3 Flashcards
What causes cancer? Control between cell death and proliferation of cells?
Cancer is caused by instability of the genome.
Throwing away of bits of core machinery results in CELL DEATH.
Throwing away of machinery which aims to inhibit proliferation and therefore prevent growth = CANCER
What is the overall aim of the cell cycle? How is this achieved?
Aim is to produce 2 daughter cells that are accurate copies of the parents
How is this achieved?
Growth cycle of cells (increase in cell mass)
Division or chromosome cycle :
-Genome replication
-Genome partition
What is the enzymatic cascade?
Cascade in the activity of enzymes which aims to get the cell cycle going. Happens by
DESTRUCTION of PREVIOUS enzymes
ACTIVATION of the next cohort along of enzymes needed.
What are the time lengths of the cell phases?
G1 – 10 hours
S – 7.5 hours
G2 – 3.5 hours
M – 1 hours
How can the length of time taken for S phase be determined?
Can be done using an in vivo assay.
32P (RADIOACTIVE ISOTOPE of phosphorus) istaken up by a cell and incorporated into the DNA sugar-phosphate backbone
Black spots on a film can be seen where radioactivity (32P) present.
DNA synthesis can then be seen – can determine the number of cells synthesising DNA (~35%)
Whatever the doubling time of the cell (time for replication) – 35% of that time is S phase
35% of 20 hours = 7.5 hours
How can we determine the length of time taken for M phase?
MORPHOLOGICAL MARKERS can be used
Anti-tubulin antibodies stained by epifluorescence microscopy
Can visualise the formation of the mitotic spindle and metaphase plate (imaginary structure where mitotic spindle forms and attaches)
5% of cells in test seen to be in metaphase
5% of 20 hours = 1 hour therefore metaphase takes 1 hour
Why do tumours form?
Tumours result because cells have lost the ability to assemble and create tissues of normal form and function OR cells are diseased
What is hyperplasia?
Invasive, abnormal tissue growth containing excessive number of cells
Using Xenopus to investigate properties of tumour cells?
Oocytes grow without dividing for month – arrested in G2 phase of the cycle (diploid)
1.5 mm in diameter
Each cell division in the early embryo 13 mins
Produces eggs on demand
Injection of progesterone will trigger release of eggs
Rapid G1 and S phases – every cell division takes 30mins
First 8 cells cycle generations – no change in size in the embryo
Centrifugation of Xenopus egg creates a protein and lipid extract in the test tube
Concentrated cell extract preserves the functional mRNA
Extract can carry out protein synthesis itself
Add any source of chromatin or DNA (acquires histones) added will acquire a nuclear envelope – forming nuclei that can carry out DNA replication and mitosis
You can observe and measure this replication and division
All the growth of the egg cells happens prior to fertilisation as an oocyte
Cyclins and using them to study the cell cycle?
Cyclins are proteins that are expressed at different levels during the cell cycle
Cyclins bind to specific kinases (Cdks) to activate
Cdks phosphorylate many proteins that are specific to certain stages of the cell cycle
RAO AND JOHNSON - fusion of cells and comparison of interphase and mitotic cells?
Take cells and infect them with virus that causes cells to fuse together
Creates cells with multiple nuclei
Fused cells in interphase along with cells in mitosis
Fusion of interphase and mitotic cells causes interphase cells to enter mitosis prematurely regardless of where they are in the cell cycle
Means that Mitosis is somehow dominant ?
Musui - use of an egg and an oocyte / transferring cytoplasm from one to the other?
Took an oocyte (arrested in G2 gap 2 resting phase)
When eggs laid by female they are in metaphase of a meiotic division – set of chromosomes aligned on a metaphase plate, just before anaphase – this means that they are ready for fertilisation
Took cytoplasm from a mature egg and injected it into an oocyte
This induced entry into M-phase in the oocyte under the influence of MPF (maturation promoting factor)
White spot appears at the top of the animal hemisphere during maturation of an oocyte to an egg
Isolated fractions with MPF activity were exposed and incubated with histone H1 and radioactively labelled ATP – there was protein kinase activity in these fraction
MPF is a protein kinase as RADIOACTIVE PHOSPHATE was transferred to the histones by the contents of the fraction.
PRINCIPLES OF THE CELL CYCLE
- activity of kinases?
- cdks
- how else are cdks controlled other than cyclins?
The simple 2 phase cell cycle control system is a protein kinase based machine
Transition into M phase driven by the action of activated cdk
Regulation of the activity of Cdks not controlled alone by the binding of cyclins
Additional regulation going on
Screening yeast and mammalian cDNA libraries for genes similar to Cdc2 (responsible for mitosis) and cyclin B led to the identification of a lot of similar genes to cdks
What causes the cell cycle to be irreversible?
Periodic destruction of a key component - cyclin
Function of cyclins
Activate catalytic subunit to allow progression of the cell cycle
Target catalytic subunit (cdk) within the cell to specific substrates
