cell division (mitosis and meiosis) Flashcards
stem cells
can use to repair cellular loss/damage
most tissues retain a population of stem cells
terminally differentiated cells
lose the ability to undergo mitosis
cannot create more cells but have continuous differentiated function
enter G0
facultative dividers
can switch between doing it’s job and making more cells
G0 phase
cells that lose the capacity for cell division enter an extended G0 phase
can be permanent (terminally differentiated) or reversible (facultative dividers)
Mitosis phases
interphase
prophase -> prometaphase (end of prophase)
metaphase
anaphase
telophase
interphase
resting phase
time between divisions
occupies most of a cell’s life
subphases = G1 S G2
G1
1st and longest gap phase
last hours to days
hypertrophy
increase in cell size
occurs in G1
hyperplasia
increase in cell number
occurs during mitosis
S phase
= synthesis
replication of DNA -> starts at 2n ends at 4n
following replication each chromosome contains 2 chromatids connected by centromere (sisters chromatids)
G2
second gap phase
preparation for mitosis
synthesis of ATP
synthesis of tubulin for mitotic spindle
3 checkpoints for mitosis
- G1 checkpoint = end of G1 phase
determines if cell is big enough / has proper proteins for S phase
if not cell enter G0
- DNA synthesis checkpoint = during S phase
checks for correct DNA replication -> continues to M (mitosis)
- Mitosis Checkpoint = during mitosis (M phase)
checks for completed mitosis
if so cells divides and repeats cell cycle
M phase
cell division portion of mitosis
charactered by karyokinesis followed by cytokinesis
creates 2 daughter cells that are as identical as possible
karyokinesis
division of nucleolus
cytokinesis
division of cytoplasm
when do chromosomes condense in cell cycle
during S & M phases
chromosomes become visible and look like coiled snakes
when are chromosomes an unraveled mass
G1 & G0
prophase
first phase
chromosomes visibly condensed / not necessarily organized
microfilaments and microtubules of cytoskeleton disaggregate
centrioles migrate to poles of cell and form spindle apparatus with interpolar microtubules
prometaphase
late prophase
nuclear membrane and nucleoli gone
mitotic spindle attaches to chromosomes at kinetochore
metaphase
chromosomes line up along metaphase plate
anaphase
centromere split apart
chromosomes migrate to opposite ends of cell
pulled by microtubules connecting centriole and kinetochore
*Dr. M. Cole’s favorite phase
mitotic spindle
controls distribution of chromosomes in daughter cells
how do chromosomes move
through the addition and subtraction of tubulin subunits and attachment proteins (dynein and kynesin) to chromatids
Telophase
mitotic spindle disaggregates
nuclear envelope reassembles / nucleoli reappears
plasma membrane forms cleavage furrow
cytokinesis begins
Mitotic index
count # of cells going through mitosis
used to describe proportion of cells in a tissue in mitosis at any given time
important in tumors
Meiosis
reduction division = makes cells with half genetic info
haploid gametes for egg and sperm cells
occurs only in germ cells of gonads
male = spermatogenesis
female = oogenesis
fusion of gametes
produces a diploid zygote (fertilized egg)
First meiotic division
w/ pro- meta- ana- and telophase
results in formation of 2 daughter cells
how meiosis different from mitosis
during prophase 1 homolgoous pairs of chromosomes form tetrads and exchange chromatin through crossing over
results in hybrid chromatids different from parents
end of meiosis = 4 haploid gametes
Second meiotic division
brief interphase II NO DNA replication
NO crossing over during prophase II
Anaphase II centromeres spilt
Telophase II cytokinesis yields four haploid gametes EACH UNIQUE
how many viable gametes produced by gametogenesis
male = 3 or 4 viable gametes
female = 1 functional gamete (ovum)
2 or 3 non functional polar bodies
spermatogenesis begins
at puberty
oogenesis begins
during fetal development
female germ cells enter prophase I 5th month of gestation and stop
remain in prophase I until ovulation (12-50 year)
apoptosis
cell death
triggers of apoptosis
timing in fetal development
some cells have predetermined life spans (skin cells ; GI tract)
growth and regression of ovarian follicles
destruction of virus / tumor infected cells
clonal deletion in thymus = removal of t cells that react to self molecules
failure of clonal deletion
may lead to autoimmune diseases
Apoptosis begins with
pyknosis = the shrinkage of nucleus and condensation of nuclear chromatin
Autolysis
lysosomes release catalytic enzymes into the cytoplasm
when a cell is apoptosis-ing what color does it become
bright pink / eosinophilic
the final pathway of apoptosis is initiated by ____
caspace cascade
normally inactive enzymes are turned on to help with degeneration and fragmenting the nucleus
Karyolysis
chromatin in nucleus begins to degenerate
karyorrhexis
nuclear material begins to fragment and nuclear membrane disintegrates
apoptotic bodies
fragmented nuclear debris
(dead) necrotic cells phagocytosed by macrophage and neutrophils
necrosis
not natural death
death of cells as a result of inflammation traumatic injury or pathology
