The Eukaryotic Cell Cycle Flashcards
What is a cell cycle?
series of cyclic events for cell duplication and division, essential for all
living things to reproduce/grow
What type of cells rarely divide?
- muscle cells
- nerve cells
What type of cell divides only once a year or two?
cells in the liver
What type of cells divide twice a day?
cells in the gut
What are the four phases of cell division?
- G1
- S phase
- G2
- M phase
What is the G0 phase?
a resting phase where non dividing cells reside
What is M phase comprised of?
- mitosis
- cytokinesis
Where does the cell cycle control system checkpoints occur?
- between G1 and S phase
- between G2 and M phase
- between metaphase and anaphase
What do these checkpoints do?
It ensures that all the events required in each phase
are completed before the next one begins
▪ If not, it halts the cell cycle
▪ or enter the G0 resting phase (outside cell cycle)
▪ or activate apoptosis
What is a cdKS?
Cyclin-dependent kinases
What happens in Cdk activation?
- Cdks require specific cyclins to become active
- cyclins regulate the activation of Cdks
- Cdks have to be phosphorylated to be active
What happens in the G1 phase?
Period of metabolic activity, cell growth, and
general repair to prepare the cell for division
What happens in the S phase?
In the S phase, each chromosome (nuclear
DNA) is replicated
▪ S-Cdk activates helicases and other enzymes
to initiate DNA replication
▪ Chromosomes are not yet visible in their X-
shape; they exist as chromatin
What is a centrosome?
- centrosome is a cellular structure that controls the microtubules organisation within the cell
What happens in the G2 phase?
- rapid cell growth and protein synthesis in preparation of mitosis
- through check for unreplicated/ damaged DNA
What are the stages in M phase?
mitosis
cytokinesis
What happens in the prophase?
chromatin is condensed into distinct visible chromosomes
* all nuclear activities are ceased
* outside the nuclear, mitotic spindle assembles between the 2 chromosomes which have begun to move apart
What happens in the prometaphase?
- Nuclear envelope disintegrates
- The 2 centrosomes are at the spindle poles (opposite ends) of the cell
*Chromosomes are attached to spindle microtubules of one pole via their
kinetochores
What happens in metaphase?
- mitotic spindle is fully developed
- Kinetochores on each sister chromatid attach to opposite poles of the spindle
- The chromosomes are aligned on the spindle equator
- M checkpoint controls the proper chromosome alignment and attachment
What happens during anaphase?
- Cohesins, holding sister chromatids together, break down → X-shaped chromosomes
▪ Because kinetochore microtubules shorten and the spindle poles also move apart - Sister chromatids of each chromosome segregate (now individual chromosomes)
and are pulled toward the opposite spindle poles
What happens in the telophase?
- The two sets of chromosomes arrive at the spindle poles and decondense
- It starts the cytoplasm division → formation of the contractile ring, between poles
- Nuclear envelopes and lamina reassembles around each set of chromosomes,
➢formation of two nuclei → final event of mitosis
What happens in cytokinesis?
The cytoplasm is divided in two by the contraction of contractile ring, which
pinches the cell into two daughters → each with one nucleus (same DNA)
What is apoptosis?
Programmed cell death induced by internal and external stimuli
When does apoptosis happen?
- removing cells during embryonic development
- cells no longer needed
- cells with severe DNA damage
- cells infected by viruses (prevents damage to neighbour cells)
What is necrosis?
cell death due to acute injury
* non-controlled event → cells rupture = inflammation
What do initiator caspase do?
- can activate downstream capases
- which break down key proteins
What does not enough apoptosis lead to?
- can allow cancer cells to grow
- disease to spread
What does too much apoptosis lead to?
- excessive cell loss
- e.g Alzheimers due to loss of neurones
