Mitosis Flashcards
How is the cell system controlled in eukaryotic cells?
Intracellular control: checkpoints at end of G1/ G2 and M phase
Requires cyclin dependant protein kinases
Intercellular control:
Mitogens/ growth factors (stimulate cell growth)
Survival factors (promote cell survival and inhibit apoptosis)
Explain the role of growth factors in the control of the cell system
They are signalling molecules which bind to the cell surface
- activate pathways which control genes
-have multiple effects but they are MITOGENIC (they stimulate mitosis or cell division)
-act by stimulating cells to enter G1 or G0
Maintain correct cell number in an organ. system
Discuss which pathways the growth factors activate in intercellular control
- RTKs, RAD and MAPK
- These pathways result in the activation of Myc
- Myc acts increase the expression of G1 cyclin kinases
- STIMULATES DNA SYNTHESIS
What does MYC do?
- Increases expression of G20kinase
- INCREASES DNA SYNTHESIS
What is the impact of excessive Myc?
-Produces Arf
What does Arf do?
Binds to the p53 inhibitory protein which results in cell cycle arrest of apoptosis
What is cell cycle arrest?
- DNA damage activates kinase proteins
- The kinases phosphorylate p53
- p53 activates p21
- p21 causes cell cycle arrest or apoptosis
What is the difference between meisosis 1 and meiosis 2?
1= segregation of homologous chromosomes (crossing over) 2= segregation of non homologous chromosomes
What are the 5 stages of Prophase 1?
- Leptotene: chromosomes visible
- Zygotene= homologous chromosomes pair up
- Pachytene= crossing over
- Diplotene= chromosomes move apart but bivalents still attached
- Diakeneses= transition to metaphase
What is independent assortment?
-Random orientation of homologous chromosomes at metaphase of meiosis 1
What is recombination?
Crossing over= recombination of genes
A recombinant chromosome contains genes from 2 parents
What is X chromosome inactivation?
One of the X chromosomes a female inherits is inactivated during embryonic development
-Involves methylation of the DNA and expression of XIST
What does Aneuploidy result from?
The fertilisation of gametes in which the chromosomes have remained linked together
What is the definition for a monosomic zygote?
-Has only one copy of a particular chromosome
What is a trisomic zygote?
-Has 2 copies of a particular chromosome
