CELLULAR BIOLOGY Flashcards
- Cell Cycle - Cell Death
What are the phases of the cell cycle?
- G1 phase
- S phase
- G2 phase
- M phase
- G0 phase
Which phases of the cell cycle are collectively referred to as interphase?
- G1 phase
- S phase
- G2 phase
What is the G0 phase of the cell cycle
A non-dividing state
What is quiescence?
Cells in G0 phase temporarily and can return to G1 phase in response to external stimuli
List the different tissue categories based on the rate those tissues undergo cell division/go through the cell cycle
give examples for each
- Labile tissues: frequently dividing cells e.g. skin cells
- Stable tissues: cells which divide in response to stimuli e.g. liver cells
- Permanent tissues: non-dividing cells e.g. neurones, skeletal muscle and cardiac muscle cells
What is senescence?
Cells is senescence are metabolically active but can no longer divide
How do cells enter senescence?
Telomeres one each end of the chromosomes shorten with each cell division, eventually these telomeres are shortened so much that the cell stops dividing and enters senescence
Which cell types do not enter senescence?
- Stem cells
- Pathogenic cells
- Neoplastic cells
How do certain cells prevent senescence?
The telomerase enzyme synthesises telomeres back onto each end of the chromosomes
How does the G1 checkpoint regulate the cell cycle?
Checks for:
- cell growth
- nutrients
- presence of growth factors (mitogens)
- DNA damage/mutations
How does the G2 checkpoint regulate the cell cycle?
Checks for:
- Completion of DNA replication
- DNA damage/mutations
How does the M checkpoint regulate the cell cycle?
Checks for:
- chromosome attachment to spindle fibres at the metaphase plate during metaphase
What are the two tumour suppressor proteins?
- p53
- pRb (retinoblastoma)
How does p53 regulate the cell cycle?
- DNA damage/mutations stimulate p53
- p53 stimulates the cell to enter G0 phase (to allow for DNA repair) or apoptosis
How does pRb (retinoblastoma) regulate the cell cycle?
- Un-phosphorylated Rb inhibits the transcription factor E2F
- The presence of mitogens stimulates cyclin D synthesis
- Cyclin D forms are activated complex with CDK-4 and CDK-6 known as the Cyclin D/CDK-4&6 complex
- This complex phosphorylates Rb, causing the transcription factor E2F to dissociate from Rb and activate gene transcription, allowing the cell to move from G1 to S phase