Block 2. Lecture 10. Cell division. Flashcards
3 possible cell destinies
- live and function without dividing
- grow and divide
- die( can be a good thing)
Explain diversity even though DNA in every cell is the same.
Gene expression
The same gene can produce different proteins
Varies depending on the cell function/ location.
Somatic cell division is called
Mitosis
diploid(2n) to diploid(2n)
Reproductive cell division is called
Meiosis
diploid(2n) to haploid(1n)
Why do somatic cells divide
- growth and development
- tissue renewal
- results in 2 daughter cells that are identical to parent cell
not all somatic cells divide
Give examples of somatic cells that do not divide
muscle, nerve
give examples of somatic cells that divide a lot
skin, blood, liver etc
What phase are cells in for most of the time?
interphase
What are the 3 components of interphase
G1 ( growth or gap phase 1)
S(DNA synthesis duplication)
G2( growth or gap phase 2)
what happens during DNA synthesis
DNA strands are separated at the hydrogen bonds holding the nucleotides together
new strands of DNA is synthesized opposite each of the old strands.
Phases of eukaryotic cell cycle
PMAT
Prophase( early and late stage)
Metaphase
Anaphase
Telophase and cytokinesis
Prophase
Anaphase
Chromosomes are pulled apart by microtubules to each side of the cell.
(Mitotic spindles attach to centromeres on the chromosomes. )
How many chromosomes are in each cell
46 total
23 from mom, 23 from dad
DO NOT EXIST IN PAIRS. ONLY WHEN DUPLICATED
What controls cell division making sure there are no mistakes occurring along the way
cell cycle checkpoints.
Checkpoint functions
G1:
is the DNA undamaged?
is the cell size and nutrition ok
Appropriate signals present?
if not- exit to G0
G2:
prevents cells from entering mitosis when DNA is damaged, providing an opportunity for repair and stopping the proliferation of damaged cells.
M:
Are all chromosomes attached to spindles?
What are the key proteins involved in checkpoints?
cyclin, Cdk, MPK
Where does Meiosis occur
gonads(ovaries and testes)
produces gametes which are haploid( a single set of 23 chromosomes)
Fertilization restores the diploid number of chromosomes
Produces cell genetically different from the parent cell
two stages of meiosis
miosis 1
miosis 2
Meiosis 1 differences from mitosis
where most significant differences from mitosis
PMAT
pairs of homologous chromosomes form in prophase ( pair consists of 2 DUPLICATED CHROMOSOMES 1-paternal 1 -maternal from YOUR PARENTS). In prophase nuclear envelope breaks.
Crossover happens between maternal and paternal chromosome pairs( RECOMBINATION)
During metaphase the crosslinked chromosome PAIRS split, with each DUPLICATED CHROMOSOME going to each end. SISTER CHROMATIDES REMAIN ATTACHED.
Chiasmata
the recombination that happens between non-sister chromatids in Prophase 1 of Meiosis 1
kinetochore
a place where the kinetochore microtubules attach to chromosomes/chromatids
the protein complex assembled at each centromere serves as the attachment site for spindle microtubules
tetrad
4 chromatids bound together( 2 duplicated chromosomes)
difference between meiosis 2 and mitosis
not preceded by DNA replication(happens in meiosis 1)
results in 4 haploid cells
products of meiosis
4 haploid cells genetically different from the parent cell
When does synapsis of homologous chromosome NOT occur?
mitosis
Sources of genetic variation as a result of meiosis
- crossing over at prophase 1 (1-3 crossover events per pair)
- independent assortment at metaphase( 2^23 > 8 million possible combinations)
- fusion between two gametes( > 2^23 times 2^23 combinations). WHEN THE EGG AND THE SPERM CELLS MEET THE VARIABILTY INCREASES.
how are sister chromatids attached to each other?( in some species)
by protein complexes called cohesins. Sister chromatid cohesion.
Each sister chromatid also has a centromere
cytokinesis
Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells. It occurs concurrently with two types of nuclear division called mitosis and meiosis, which occur in animal cells.
Where does the material for mitotic spindles come from?
While the mitotic spindle assembles, the other microtubules of the cytoskeleton partially disassemble, providing material to be used for the construction of the spindle.
they elongate by incorporating more subunits of the protein tubulin
in what phase does the nuclear envelope dissociates?
late prophase
when do mitotic spindles start to form
early prophase
what are mitotic spindles made out of
consists of fibres made of microtubules, made of the protein tubulin,
where does the assembly of mitotic spindles happen
the assembly of spindle microtubules starts at the centrosome( the pair of centrioles at the center of the centrosome are not essential for cell division).
what happens to centrosomes during interphase?
they duplicate
How many centromeres does a duplicated chromosome have?
1 shared between 2 chromatids
BUT each individual chromosome will have it before replication.
difference between kinetochore and centromere
The main difference between centromere and kinetochore is that centromere is the region where the two sister chromatids are held together after the replication of chromosome where kinetochore is the protein complex on the chromosome where spindle fibers are attached during cell division.
Homologous chromosomes
Homologous chromosomes are chromosomes that share: The same structural features (e.g. same size, same banding patterns, same centromere positions) The same genes at the same loci positions (while the genes are the same, alleles may be different)
