Chapter 9 Flashcards
What are the 4 phases of the cell cycle?
G1, S, G2 and M
What happens in the S phase?
Replication of genome
What happens in the M phase?
Segregate the replicated genome into two daughter cells
What is G0?
A quiescent state in which a cell cease proliferation because of insufficient nutrients, lack GF or upon differentiation.
What is a replication fork?
When DNA polymerase is attached to ssDNA, and replicate the DNA so leaving 2 dsDNA in its wake.
How does a cell ensure that each stretch of DNA is replicated only once?
By allowing each DNA replication origin site to “fire” once pr. cell cycle. Each initiation site will be bound by a pre-prereplication complex which assemble after mitosis, and when it is bout the origin site is licensed for replication.
Define cytokinesis
The process where a mother cell splits into two daughter cells.
What are the phases of mitosis?
Prophase, prometaphase, metaphase, anaphase, telophase (some include an interphase before prophase)
Which factors are deciding if a cell is allowed to enter S-phase?
A combination of extra and intracellular signals, in addition to proximity to neighboring cells. The external ligands are usually referred to as growth factors
What is the restriction point and where in the cell cycle does it occur?
It determines the cellular response to DNA damage or other mistakes/deficiencies PRIOR TO REPLICATION- ie. it is there to repair mutations that has occurred independently of mistakes that can occur during replication (from UV light, carcinogens, radiation etc)
What happens to the restriction point in cancer cells?
The control over the restriction point is loosened, as the cells proliferate without the appropriate combination of extracellular signals.
Name two molecular mechanisms which are particularly central to cell-cycle regulation
Cyclin-dependent kinases and E3 ubiquitin ligases
How are CDKs activated?
By binding to CYCLIN, which leads to phosphorylation of the CDK and their activation. CYCLIN also influences substrate selection by the CDK and specify the intracellular location of CDK activity
Which cell function is dependent on ubiquitin mediated proteolysis?
Destruction of important cell cycle proteins
Name the different cyclin and CDK combinations which have been best documented?
CDK 1 + A/B
CDK 2 + A/E
CDK 4/6 + D
CDK 7 + H (works as an activator for other CDKs)
Name 2 important inhibitory control mechanisms of CDKs
MYT1 and WEE1, and CDK inhibitors such as INK4/CIP/KIP
How does the intracellular level of cyclins vary through the cell cycle?
No variation of cyclin D throughout the cell cycle, high levels of A and B through S and G2, very low through M and G1.
When is the cells restriction point in the cell cycle?
In G1- will need to pass through the restriction point to enter S-phase
What may be the causes for a cell to arrest in G1?
DNA damage, lack nutrients, excessive contact neighbour cells, too small in size, lack of extracellular growth factor stimulus
Where in the cell cycle are the checkpoints?
G1, S and G2/M
How is cell arrest induced in G1 due to genome damage?
DNA damage autophosphorylate ATM/ATR, together with DNA-PKs they activate multiple proteins which form a platform on which repair proteins can assemble. They also stabllize P53, which works as a transcription factor for p21 which is and CDK D/E, cyclin 1 inhibitor resulting in cell cycle arrest.
What are the 2 cell states and which CKDs are high when?
Anaphase to S1 - low CKD 1 and 2, high APC/C
What is the molecular basis of the restriction point in G1?
Growth factors stimulate cyclin D-CDK 4/6 which phosphorylates the 3 proteins Rb, p130 and p 107- they are released from the transcription factor E2F = allow E2F to promote transcription of Cyclin E and Cyclin A. This overturns the G1 state resulting in elevated CDK 1+2 activity and the cell enter S-phase.
Which known oncogene is involved in cell growth?
c-MYC
How can c-myc stimulate the cell cycle?
By activate transcription of cyclin D1, cyclin D2 and CDK4 or by suppress genes encoding for 21 and p15
Which cell signalling network regulate cell growth and are often involved in the oncogenic process?
mTOR, PI3K through AKT and TORC1 activation or downregulation of PTEN
Which effect associated with altered cell metabolism or hypoxia has been hypothesed being involved in producing building blocks for cell growth, adding to the theory of why cancer cells alter the glycolysis metabolism?
The Warburg effect
Which morphological changes are seen in a cell undergoing apoptosis?
Rounding, plasma membrane blebbing, cytoplasm shrinkage, alteration of membrane symmetry, condensation and fragmentation of the nucleus
Which morphological changes are associated with necrotic cells?
Swelling of the cell and cytoplasmic organelles, followed by focal membrane rupture
What is anoikis?
apoptosis induced by lack of cell-matrix interactions
How is cyclin dependent kinases regulated in the cell?
- Activation is dependent on temporal expression and destruction of cyclins
- The cyclin/CDK complex is regulated by phosphorylation
- The cyclin/CDK activity can be repressed with phosphorylation of serine/threonine resiudes
- CDKs are also regulated by CDK inhibitors - INK4a family (mainly work on CDK4 and 6 to inhibit biding to cyclin D) and CIP/KIP (inhibit mulitple CKDs)
How does the cell overcome the restriction point?
GF result in phosphorylation of Rb, causing release of E2F- which allow transcription of DNA replication factors and cyclin E+A - cyclins needed for activation of CDKs in S phase- called the molecular switch
Is restriction point and G1 check point the same?
Yes
What is checked at the 3 checkpoints in the cell cycle?
- The integrity of the DNA is assessed at the G1 checkpoint.
- Proper chromosome duplication is assessed at the G2 checkpoint.
3, Attachment of each kinetochore to a spindle fiber is assessed at the M checkpoint.
Explain the restriction point:
GF activate cyclin D/CDK 4/6 by phosphorylation - which will phosphorylate Rb - letting go of E2F.
When released E2F works as transcription factor for DNA synthesis factors and Cyclin A and E needed for the cell to proceed through the restriction point.
Which kinases are responsive to DNA damage?
AKT and ATR
What is the limiting factor of proliferation in normal tissue - cell cycle events or cell growth to a size where the cell large enough to divide=
Cell growth
Which cellular pathways are most important for stimulation of cell growth?
IP3K - AKT - mTOR & c-MYC activation
What type of. gene (Onco or TSP) is CDKN2A, and which canine cancer is it familial?
Histiocytic sarcoma
How can aneuploidy contribute to cancer?
- Cause greater genetic variation
- May cause alteration in protein expression resulting in advantage allowing rapid adjustment to stressors
How can aneuploidy occur?
- genomic instability - fail to properly segregate one sister chromatid to each daughter cell
- extra centrosomes- result in spindle formation with more than 2 spindles resulting in 3 or more daughter cells
- tetraploid cells can arise if anaphase or cytokinesis fail
