Cell division & Death - Week 5 Flashcards
Name the stages of mitosis & outline the key events that occur at each step
-Prophase- chromosomes condense
-Metaphase- chromosomes align at the equator, sister chromatids attach to opposite poles by Kinetochore complex.
-Anaphase: cohesive links between sister chromatids released & kinetochore microtubules shorten-(results in sister chromatids being pulled at opposite poles)
-Telophase: daughter chromosomes reach the poles & new nuclear envelope forms from individual chromosomes
Describe the roles that the cytoskeleton plays in co-ordinating in some stages in mitosis (4 points)
- nuclear lamina needs to disassemble prior to mitosis
- Actin cytoskeleton is involved in ring contraction during cytokinesis
- Microtubules have the major role in cellular arrangement
-kinetochore microtubules- attach to the chromosomes during: Prometaphase, metaphase(motor proteins +&- pull chromosomes around until aligned) & anaphase(the microtubules shorten & motor proteins move the chromatids towards the centrosome)
State when the three checkpoints in the cell cycle occur and describe what checks occur at each checkpoint
1) restriction point (end of G1)- environmental check (growth factors, cell size..)& DNA damage check
2) G2-M transition- check (cell size), DNA damage check, replication complete)
3) Meta-Anaphase transition- checks if chromosomes are attached
Explain why it is necessary to undergo meiosis for the production of
reproductive gametes
as the parents randomly distribute one set of chromosomes to each gamete, recombination increases the possibilities of having many different genes.
how is the cell cycle controlled
-Cyclins: needed to turn on the Cyclin Dependant Kinases (Cdks), Levels of cyclins rise and fall (cycle) during cell cycle.
Different Cdk-cyclin complexes regulate
transition through different stages of cell cycle e.g. M-Cdk regulates G2-M transition (active) & meta-anaphase transition (degraded)
-Kinases phosphorylate target proteins
e.g. M-Cdk phosphorylates:-
Nuclear lamins to trigger their depolymerisation
Microtubule accessory proteins: increases the microtubule instability
Chromosome condensation complex is activated by M-Cdk
Explain what is meant by the terms haploid and diploid
haploid= One copy of each chromosome
Diploid= Two copies of each chromosome (except sex chromosomes in males)
Explain how the alignment of homologous chromosomes during meiotic
prophase I enables recombination between maternal and paternal copies
-homologous chromosomes align & linked by synaptonemal complexes
- pairs of chromosomes coil; crossing over
What homologous chromosomes mean?
Two chromosomes in a pair – normally one inherited from the mother and one from the father.
Fully describe the differences between the products of mitosis and meiosis
-meiosis produces 4 haploid gametes, mitosis produced 2 diploid cells
- meiosis has 1 copy of each chromosomes per gamete, mitosis produces 2 copies of each chromosome per cell
-meiosis produces 4 genetically different cells, mitosis produces 2 genetically identical cells
Summarise the main differences between programmed cell death (apoptosis) and necrosis
necrosis- is accidental death following acute insult (e.g trauma, lack of blood), cell swells & bursts- contents release & cause inflammation
apoptosis-cells die in an organised manner and are engulfed & digested- no inflammation
Give examples of programmed cell death in development and in protecting the adult organism
apoptosis, autophagic cell death is used cells that have been around in the body long enough that they’re kind of worn out if not cancer can occur
Describe the key morphological and biochemical changes that occur during apoptosis
- cell surface ‘bleb’ appearance
- shrinkage of cell & nucleus
-cleavage of nuclear proteins and DNA/ DNA fragmentation - nucleus fragmentation
Outline the role of caspases in triggering apoptosis
caspases are firstly synthesised as inactive procaspase- small number of inhibitor caspase activate a cascade generating lots of effector (executioner) caspases- activation by cleavage
what does the caspases cascade do & what is it
the caspases are cell death proteases that promotes structural change
What sets off the caspase cascade? (include intrinsic and extrinsic pathway)
intrinsic pathway:
Switched on by damage or stress
Damaged mitochondria release cytochrome c (electron carrier) Cytochrome c in the cytoplasm activates one of the initiator caspases (9)… which activates the cascade
extrinsic pathway:
Proteins from other cells bind to Death Receptors on the cell surface
Death Receptors aggregate and cause caspase 8 to be cleaved… which activates the cascade
