cell cycle Flashcards
explain the what happens to cohesins when microtubules bind to centromeres
cyclins break down along the length of the chromosome apart from at the centromere
these cohesins break down last to prevent aneuploidy
name some cohesinopathies
Roberts syndrome
Conerlia de Lange syndrome
Non-disjunction of chromosomes
what are CDKs?
cyclin dependent kinases - regulate progression of the cell cycle
what activates CDKs?
cyclins
what does the retinoblastoma protein do?
inhibits E2F proteins by binding to them
stops cells from going past G1 into S phase
what happens when Cdk2 is activated?
inactivates Rb by phosphorylation so E2F is released so the cell can enter S phase
explain the role of p53 in controlling the progression of the cell cycle
p53 is a transcription factor
binds to the gene for p21
p21 controls whether or not cyclin-Cdk2 can activate E2F by phosphorylating Rb
how does the mutation of the RB1 protein lead to cancer?
mutation means no functional Rb
no Rb binds to E2F
E2F doesnt stop cell from entering S phase
uncontrolled proliferation –> cancer
what are the three cell cycle checkpoints?
end of G1
G2-M transition
Mitosis (metaphase)
what happens at the end of G1 checkpoint?
checks cell size, growth factors and DNA damage
controlled by p16 which inhibits CDK 4/6 so it cant interact with cyclin D
what happens in the G2-M checkpoint?
checks DNA replication, damage and cell size
stops cell cycle if there’s damage
what happens in the mitosis checkpoint?
checks that the chromosomes are attached to the spindles
what are the three main types of chemotherapy?
anti-mitotics
biologics
antihormonal drugs
what are the two classes of anti-mitotics?
vinca-alkaloids
taxanes
what do vinca alkaloids do?
prevent microtubule formation
metaphase cannot occur
what do taxanes do?
prevent the microtubule disassembly
cells cant enter telophase
what are biologics?
monoclonal antibodies
when are anti-hormonal chemotherapies used for?
hormone driven cancers
caused by overexpression of a receptor or sensitive to a hormone
what stages form interphase?
g1
s
g2
what happens during G1 and G2?
no DNA synthesis
environment is monitored
what happens in G1?
Monitors internal and external environmental conditions to ensure it is suitable for mitosis.
what happens in G2?
double checks DNA has been copied properly. Any mistakes are repaired, if they are unable to be repaired the cell undergoes apoptosis
what happens in S phase?
DNA replication
2n to 4n
what are the stages of mitosis?
o Prophase o Metaphase o Anaphase o Telophase o Cytokinesis
what happens in prophase?
- DNA condenses into visible chromosomes
- nucleoli disappears
- nuclear membrane breaks down
- chromosomes join at the centromeres
- centrioles move to the poles in pairs
- microtubules radiate and attach to chromosomes
what is the kinetochore?
how microtubules attach to the centromere of a chromosome
describe the structure of the kinetochore
inner region - binds to centrosome (present throughout cell cycle)
outer region - interacts with microtubules (made during cell division)
what happens during metaphase?
- Kinetochore / microtubules are used to pull chromosomes apart – one from each pair of sister chromatids pulled towards opposite ends
- Chromosomes line up in the middle
- Centrosomes are at the polar ends of the cell
what happens in anaphase?
- Sister chromatids are separated by the microtubules
- Chromatids are pulled to polar ends
- When chromosome reaches centrosome the poles separate further by elongation of the polar microtubules
what is cohesin?
a protein to hold sister chromatids together
what is aneuploidy?
presence of abnormal number of chromosomes
how can aneuploidy occur?
if kinetochore doesnt attach to the microtubules properly so the sister chromatids dont separate
if cohesin doesnt break down so the chromatids dont separate
what happens in telophase?
- chromosomes arrive at polar ends
- uncoiling of chromosomes
- nuclear envelope reforms
- cell’s pinched until it cleaves and forms 2 daughter cells
what happens in cytokinesis?
- Cytoplasm splits between the 2 cells
* Cell divides
what is the purpose of meiosis?
specialised cell division to make gametes
when does recombination occur?
prometaphase I of meiosis
what happens in prophase I?
Recombination/crossing over.
o Microtubules and proteins extend across the cell. Membrane around the nucleus of the cell erodes and the chromosomes are set free
what happens in metaphase I?
Chromosome pairs line up. Random assortment
what happens in anaphase I?
spindles pull chromosome pairs apart
what happens in telophase I?
Chromosomes finishing moving to their opposite poles
what happens in prophase II?
Chromosomes condense, forming an X structure. Membrane around nucleus dissolves and chromosomes are released. Centrioles duplicate and meiotic spindle is formed.
what happens in metaphase 2?
- Chromosomes line up.
- Centrioles are located at the poles of the cell.
- Meiotic spindle attaches itself to each of the chromatids.
what happens in anaphase 2?
chromatids are split and divided and pulled to the two opposite poles of the cell
what happens in telophase 2?
Same as telophase I with the addition of cytokinesis, resulting in four gametes with distinct genetic information. Chromosomes finish moving to the poles
