cell cycle Flashcards
what is the cell cycle?
period of time between birth of cells and its production of daughter cells
how long does the cell cycle last?
at least 12 hours
what 2 phases does the cell cycle consist of?
interphase and mitotic phase (mitosis)
what is interphase?
-interval between the end of mitosis and beginning of the next
-(cell is either resting or performing its specialised work not in mitosis)
-chromosomes aren’t visible (uncoiled)
what are cyclins?
cell cycle protein molecules that help fainting the cell cycle →increases/decreases concentration
what are the 3 cyclins present in the cell cycle
cyclins:
-E (G1)
-A (S)
-B (G2)
what do cyclins do?
cyclins activate and act with cyclin dependant kinases (CDK’s)
what happens to cyclins and CDK’s after the cell cycle?
-they are degraded
-residues are taken up by ubiquitin (cytoplasm caretaker protein)
what is the G1 phase?
-growth phase→cells respond to growth factors (irreversible)
-makes molecular machinery for another cell cycle
when does G1 phase occur?
-between end of mitosis and S phase
what is G1 phase controlled by? (cyclin)
cyclin E and CDK’s
how long does G1 phase last?
-lasts for less an 2 hours or more than 100 hours
What is S phase?
-DNA is replicated
when does S phase occur?
-after G1 phase before G2 phase
what is S phase controlled by? (cyclin)
cyclin A and CDK’s
how long does S phase last
7-8 hours
what is G0 phase?
-Contain cells that do not divide but increase in number (quiescent cells)
-cells do not enter S phase
what can happen to quiescent cells during G0 phase?
→growth factors can stimulate quiescent cells to leave G0 and re-enter the cell cycle
→proteins encoded by Rb (tumour suppressor proteins) block the cell cycle in G1
what is the G2 phase?
-cell prepares for division
-ends with the breakdown of the nuclear membrane and the onset of chromosome coiling
when does the G2 phase occur?
-end of S phase and beginning of mitosis
what is the G2 phase controlled by? (cyclin)
-cyclin B and CDK’s
how long does G2 phase last
2-4 hours
what are the 2 routes cells can take after mitosis?
→Enter the cell cycle again
→Enter the G0 phase
what 2 things does the mitotic phase include
-mitosis
-cytokinesis
what happens at the end of G1 phase?
G1 checkpoint
-cell checks to see if:
→DNA is not damaged
→right proteins are synthesized
what happens during prophase?
-chromosomes are first visualized. + splits longitudinally into 2 chromatids at the centromere.
-centrioles are separated to opposite poles by microtubules of the achromatic spindle
how long does metaphase last for?
20 minutes
how long does prophase last for?
1.5 hours
what happens during prometaphase?
-nucleus membrane and nucleolus disappear
-chromosomes entangled in meshwork of microtubules
what happens during metaphase?
-chromosomes align at the metaphase plate or equator of the spindle and attach to spindle fibres
-centromere for each chromosome has bilateral disc→kinetochores
what do colchicine do?
-stops the cell division at metaphase
-prevents the formation of microtubules of the spindle
-important for karyotyping
what happens during anaphase?
-Spindle fibres contract
-sister chromatids separate and reach the opposite poles of the cell
what is nondisjunction?
-chromosomes fail to migrate properly in anaphase, so one daughter cell receives extra chromosomes and the other is deficient in this chromosome
what is an isochromosome?
-centrome splits transversely
-chromosomes of unequal length
what happens during telophase?
-nuclear membrane reforms and nucleolus appears
-Cytoplasm divides and two complete cells are formed
-chromosmes uncoil
what is cytokinesis?
cleavage furrow develops around the equator region and daughter cells separate
