Cell Cycle Flashcards
What are the 4 main stages of the cell cycle?
- G1
- S
- G2
- M
The cell cycle can also be divided into 2 phases what are these 2 phases?
- Interphase (cell not dividing, G1, G0, S, G2)
- M phase (mitosis)
The cell can go into a resting phase out of G1 what is this phase called?
G0
What are mitogens?
- Extracellular signalling molecules, usually proteins
- Stimulate cell division
- Function via cyclin dependent kinases (Cdks)
What is the difference between a mitogen and a growth factor?
Some molecules are both mitogens and GFs. Terms sometimes used interchangeably
Mitogen
- Stimulates growth via cell division
Growth factors
- Stimulates growth in size
What phase are most cells in our body?
G0
Give examples of cells in a permanent G0 state?
- Neurons
- Skeletal muscle cells
Give an example of cells which are often in G0 but may divide if stimulated?
Liver cells
Give examples of cells which may enter and exit G0 many times in their lifespan?
- Fibroblasts
- Lymphocytes
What cells are known as labile cells and rarely/never enter G0?
- Bone marrow
- GI epithelial cells
- Hair follicles
Most effected by many forms of chemotherapy
What are the 5 major phases of mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What is the shortest (most rapid) portion of the cell cycle?
M phase
- Mitosis
What occurs in prophase?
- Chromosomes condense
- Spindle fiber forms
What occurs in prometaphase?
Chromosomes organize on mitotic spindle
What occurs in metaphase?
Chromosomes line up on metaphase plate
What occurs in anaphase?
Chromosomes separate
What occurs in telophase/cytokinesis?
- Spindle breaks down
- Cell divides
Give some examples of points at which there is a checkpoint / restriction point in the cell cycle?
- G1-S (prior to S phase entry)
- G2-M (prior to Mitosis)
- M phase (prior to anaphase/cytokinesis)
Cyclin dependent kinases rely on cyclins which are regulatory proteins.
What do cyclin-Cdk complexes do?
Phosphorylate regulatory proteins
- Activate E2F proteins (transcription factors)
- Allow progression through cell cycle by binding to DNA prometer regions -> progression to S phase
What extracellular proteins activate Cdk?
Explain how this process works
Mitogens
- Interact with cell surface receptors
- Activate intracellular pathways
- Increase G1 cyclin levels
- Increase cdk activity
What do cyclin-Cdk complexes activate specifically?
E2F proteins
- Transcription factoes which activate genes for S phase
What proteins can inhibit E2F and therefore progression to S phase?
Retinoblastoma proteins (Rb)
What is Rb known as?
A tumor suppressor
What do cyclin-Cdk complexes phosphorylate specifically?
Retinoblastoma proteins
- Activating E2F (TFs)
What can arrest cell division at G1-S checkpoint?
DNA damage
- Allows for repair and prevension of mutant cells/cancer
What are 2 pathways which cause cell cycle arrest at the G1-S checkpoint?
- ATM pathway (ds breaks)
- ATR pathway (ss breaks)
What do ATM and ATR pathways lead to?
Phosphorylation of proteins
- Causes cell cycle / growth arrest at G1/S point
What is ATM pathway triggered by?
Double strand breaks
What is the ATR pathway triggered by?
Single strand breaks
A mutation in ATM pathway leads to what condition?
Ataxia Telangiectasia
What protein is stimulated (phosphorylated) by the ATM/ATR systems?
p53
p53 induces the transcription of what proteins?
p21 proteins
What does p21 (activated by p53) bind to to cause arrest of the cell cycle?
Cdks
- They therefore cannot activate E2F proteins
-> Arrest of cell cycle
What are p53/p21 known as?
Tumor suppressors
What is p53 generally stimulated by to cause arrest of the cell cycle?
DNA damage
Retinoblastoma is a mutation of what gene?
RB1
- Codes for Rb protein
- Abnormal Rb -> unregulated cell growth
Li-Fraumeni syndrome is a mutation of what gene?
TP53
- Codes for p53 protein
What are the main cancers that are caused by Li-Fraumeni Syndrome?
SBLA
- Sarcoma
- Breast
- Leukemia
- Adrenal gland
