Mitosis and Meiosis Flashcards
What drives the cell cycle
Cyclin-dependent kinase
How does Cdk do its job
Phosphorylating specific substrates
What happens during mitosis prophase
Chromosomes condense
Centromeres migrate to poles
Spindle starts to form
What happens during mitosis pro-metaphase
Nuclear envelope breaks down
Chromosomes attach to spindle
Mitosis metaphase
Sister chromatids linked to opposite spindle poles
Chromosomes align along equatorial plane
Mitosis anaphase
Sister chromatids separate
Daughter chromatids pulled to opposite ends of cell
Mitosis - telophase
Chromosomes arrive at poles
Nuclear membrane reforms
Chromosomes decondense
Centrosome:
Microtubule organizing center, contains a pair of centrioles
What holds sister chromosomes together
Cohesin
What helps DNA coil
Condensin
What triggers nuclear envelope breakdown
It goes to vet school
JK. Cdk phosphorylation of lamins, which provide the structural integrity
How do microtubules attach to the chromosomes
Attach to the kinetochore which is bound to the DNA
What are the names of improper spindle alignment
Syntelic
Merotelic
Monotelic
What is proper spindle attachment/orientation called
Amphitelic
Syntelic attachement:
Both kinetochores attached to the same pole
Merotelic attachments
Uneven number of microtubules between poles (more attached to one pole than the other pole)
Monotelic attachments
Microtubules only attach to one kinetochore
Astral microtubules:
orient spindles, pull centrosomes apart
Kinetochore microtubules
Pull chromatids apart
Polar microtubules
Extend the entire length of the spindle
Is tension between centromeres good or bad
Good. It means there’s a stable attachment
How do microtubules pull chromosomes apart
Fast subunit subtraction at kinetochore –> MT shortened –> kinetochore pulled toward pole
What is APC
Anaphase promoting complex
What activates APC
Cdk
What is APC’s job
To activate separase by cleaving securin
Why does separase need to be activated
Separase degrades cohesin which holds the sister chromatids together. Anaphase cannot happen until cohesin has been degraded
What happens if the chromosomes aren;t correctly aligned going into anaphase
APC is never activated –> separase never activated –> cohesin keeps sister chromatids together –> no anaphase
What is cytokinesis
Cytoplasmic division
When does cytokinesis occur
Anaphase-telophase
What is the contractile ring
Actin and myosin filaments that form inside the plasma membrane at the metaphase plate
What is the goal of meiosis
To produce haploid gametes from diploid parent cells
What aspects of meiosis contribute to genetic diversity
-Independent assortment of maternal & paternal homologs during meiotic division I
-Crossing over during prophase I
What is the primary driver of proper chromosome segregation in meiosis
Crossing over
Sparknotes of meiosis I
Duplicated homologs pair up
At least one cross-over occurs per pair
Homologs align on spindle
Homologs segregate to opposite poles
Sparknotes of meiosis II
Spindle reforms
Chromosomes align
Chromatids segregate to opposite poles
Prophase I:
Homologous chromosomes pair up
Protein elements established between homologs
Recombination (crossing over)
Where on the chromosomes does recombination occur
At recombination nodules–large protein complexes containing recombination proteins
Steps of recombination:
Double-stranded DNA break
Resected so that 3’ end overhangs
Overhanging 3’ end invades homologous chromatid
Double Holliday junction forms
Resolvase cuts joined molecules to produce recombined chromosomes
What is the site of completed cross-over called?
Chiasma
Two pairs of homologous chromosomes are called a…
bivalent
Non-disjunction:
Failure of chromosomes to separate and segregate properly at anaphase I or II
What holds pairs of homologs together
Chiasma(s/e)? is it Latin? who knows
cohesins at arms
What holds sister chromatids together
Cohesins at the centromere
Where do oocytes arrest during meiosis
Prohpase I
What is special about oogenesis in terms of divisions
They are asymmetric–one set is discarded (1st and 2nd polar bodies)
When does meiosis initiate in the male
After puberty
Why are there so many more sperms than oocytes?
Because it takes more energy and resources to create an oocyte and sperm exploit maternal investment. Classic.
Mitosis vs meiosis: where does it happen
Mi: somatic cells
Me: germ cells
Mitosis vs meiosis: what is the result
Mi: 2 diploid cells
Me: 4 haploid cells
Mitosis vs meiosis: what happens to the # chromosomes/cell
Mi: maintained
Me: halved
