mitosis/meiosis Flashcards
prokaryotes divide by
binary fission
what do chromosomes look like in bacteria?
single circular chromosome
how do bacteria replicate their DNA?
from ORI sequence- create double strand- form septum, pinch in, voila! 2 daughter cells
eukaryotes have what kind of chromosomes (shape)
linear
unlike bacteria, chromosomes exist in ___ pairs
homologous
definition mitosis
chromosomal process that ensures each daughter cell gets exact, correct copy of genetic information
at what phase of mitosis do chromosomes become visible in light microscope
prophase
define DNA packing
Positively charged Histone proteins neutralize the negative charge on DNA
what is the beads on a string model?
Octamers of histone “core” proteins (nucleosomes) wrap DNA around themselves, giving it the appearance of “beads on a string”
when would you see the most condensed form of DNA
metaphase, on sister chromatids
what does 30 mm fiber refer to
the arrangement of packed nucleosomes and DNA
when would distinct chromosomes be visible
M phase of mitosis
4 phases of cell cycle
G1, G2 S, M,
what phase are non dividing cells in? can you give an example?
G0. liver cell
Interphase is what 3 phases
G1 + G2 + S
G1
rapid growth and metabolic activity of mitosis
G2
growth and preparation for cell division
S phase
DNA replication and growth
what kind of phase are neurons always in?
G0 - nondividing
what significant event happens in S phase?
synthesis of DNA
describe a replication fork and when you’d find it
in S phase, as you replicate DNA, you go from single strand -> double strand. as this is happening, bidirectionally, you get a replication bubble and fork
Kinetochore
Kinetochore structures (made of proteins) are the attachment sites for microtubules at the centromere regions
telomeres
ends of chromatids/chromosomes
what do you call DNA in the replicated form
‘sister chromatids’
how do you identify chromosomes for a karyotype?
based on their band patterns, gleaned from electrophoresis. line up from largest->smallest
name for non-sex cells
somatic cells
what phase of mitosis is essentially a reverse of prophase
telophase- rebuild nuclear envelope, recondense
when would DNA convert back to regular old chromatin?
after cytokinesis
what does the nucleus do in interphase?
- Ribosomal RNA being copied from RNA into DNA form to assemble a ribosome
what happens in interphase nucleus that would affect the chromatin?
ex- inactive B cell (in lymphocyte) and it has a lot of heterochromatin. After it is activated to participate in immune response, the gene pattern changes and now we have a lot of euchromatin instead of heterochromatin
___ are the intermediate filaments that support the inside of nuclear envelope
nuclear lamins
__ chromosomes are in each cell during mitosis
46
kinetochore complex
centrosome + microtubule site of attachment
what’s the pac-man complex?
to move the chromosome towards the poles for anaphase, the kinetochore complex ‘eats’ the microtubules- aka depolymerizes the tubulin in the microtubules
aster fibers and who has them
- only animals have aster fibers
- they are a type of mitotic spindle that are unattached microtubules hanging off the centriole
do plant cells have centrioles?
no
kinetochore microtubules
mitotic spindle running ‘pole to kinetochore’. found in both plant and animal cells
polar microtubules
mitotic spindle running pole to pole. found in both plants and animals
what proteins perform the cleavage taking telephase to cytokinesis?
actin filaments + myosin motors act to contract the cleavage furrow until the cell pinches off
reduction divsiion
stage of meiosis I , anaphase I, where the pairs of chromosomes separate (3 replicated chromes on each side of cell) centromeres have NOT split. this is the stage where the cell finally goes from 46-> 23 chromosomes
in anaphase II, how many chromosomes are at each pole
23
when does synapse occur?
meiosis : in prophase I- line up with homologous chromosomes, crossing over occurs @ chiasmata
what are the 2 parts of anaphase
anaphase A: chromosomes pulled poleward
anaphase B: poles pulled apart
when in mitosis does gene activity resume?
telophase
when in mitosis does nucleolus reappear?
telophase
phragmoplast
- instead of pinching in, plants create a cell plate in the middle of cell
- grouping of small vesicles produced in the golgi that move along microtubules to the middle of cell
- new golgi/ER complex in replicating plant cell is the phragmoplast
when you enter prophase I of meiosis, are chromosomes already replicated?
yes
when in meiosis does crossing over occur
prophase I
what event precludes crossing over
synapse
The Thompson seedless grape is triploid, with three copies of each chromosome. Which phase of the cell cycle would you expect triploid cells to be unable to complete.
homologous chromosomes must pair in meiosis I. Triploid cells would be unable to complete meiosis I.
The stage of meiosis where cells become haploid
Separation of homologous pairs occurs at anaphase I. Even though each chromosome has two chromatids, the total number of chromosomes is 23 for humans after anaphase I of meiosis I. Recall that the number of chromosomes is determined by the number of centromeres
name the 3 mitotic spindle fibers
- aster fibers
- pole to pole fibers
- pole to kinetochore fibers
telocentric
centromere hangs out at end of chromosome
name for when centromere is in middle of chromosome
metacentric
name for when centromere is at top of chromosome
acrocentric
when would gene expression happen
interphase
of centrioles present in metaphase
4; 2 at each end (count each guy as its own!)
number of chromosomes/chromatids present at metaphase 2
chromosomes: n
chromatids: 2n
chromosomes / chromatids: anaphase 2
46, 46
chromosomes/chromatids: metaphase I
2n, 4n
chromosomes/chromatids: prophase I
2n, 4n
chromosomes/chromatids prophase II
n, 2n
mitosis: # chromosomes/chromatids in metaphase
2n, 4n
how does division in binary fission work
•split in two between plasma membrane attachment sites (involves forming a septum and pinching-in)
specific structure to which microtubules attach
kinetochore
test cross (who vs who?)
SsYy x ssyy
amount dna division versus prophase
1:2 (you get sister chromatids in prophase, 2x the DNA!)
how many chromatids are present in anaphase?
- they are all replicated, no single chromatids
