Cell Cycle, Mitosis, & Meiosis Flashcards
set of proteins the cell possess…
…determines the functions the cell can perform
G1
stockpile nucleotides, ATP, enzymes to replicate DNA
S
replicate DNA
G2
synthesize microtubules and other proteins needed for cell division, stockpile ATP and enzymes for mitosis/meiosis
M
mitosis or meiosis
G0 (G Zero)
cell stops replicating and dividing
reasons for G zero phase
suffered damage to DNA; lack of growth factors, nutrients or other molecules that are necessary for cell cycle to continue in environment; telomeres are short (time for cell to die and be replaced); some go to G0 after fully differentiated and remain in G0 until they die (neurons lack centrioles so they can’t divide red blood cells lack nuclei)
specifics of G1
phosphorylation of certain proteins (ex: retinoblastoma RB protein); at the end of G1 cell makes sure it has stockpiled all the enzymes it needs to replicate DNA before it goes into S phase
specifics of G2
cell must accumulate certain level of complex called mitosis-promoting factor (MPF) and activate it by dephosphorylation in order to enter the M phase; at end of G2 cell checks for DNA damage presence of DNA damage keeps MPF inactive and halts the cell in G2; cell also checks length of telomeres
telomere length
indicator of cell age; telomeres shorten every cell cycle
spindle assembly checkpoint
during late metaphase cells checks to be sure every chromosome is properly aligned at equatorial plane and that every centromere has been contacted by a spindle fiber; everything alined properly = MPF will be inactivated so cell can . proceed toward end of mitosis
stages of mitosis
prophase, prometaphase, metaphase, anaphase, telophase (cytokinesis)
cytokinesis
occurs during telophase - cytoplasm and organelles are divided between 2 daughter cells
end of interphase
spindle fiber apparatus (green/yellow) is not yet organized; chromatin is decondensed - no discernable chromosome in the nucleus; nuclear membrane is intact
prophase
chromatin condenses into visible chromosomes and migrates toward equatorial plate; DNA was replicated in S phase = each chromosome now has 2 sister chromatids; by late prophase you can see 2 separate sister chromatids under microscope; nuclear envelope disintegrate centrosomes move to poles of dividing cell; spindle fibers grow out of the centrosomes toward centromeres of chromosomes
early prophase
chromosomes begin to condense; centrosomes begin to move toward opposite poles of dividing cell
late prophase/prometaphase
centrosome have migrated to poles; chromosomes are condensed; nuclear membrane is gone; spindle fibers are reaching in and binding to chromosomes
metaphase
at the end chromosomes are in most condensed configuration and aligned at equatorial plane; nuclear envelope still disintegrated; spindle fibers bound to kinetochore at centromere of each chromatid - binding occurred during late prophase; cell undergoes spindle-assembly checkpoint to be sure every chromatid has been bound by spindle fiber
late metaphase
chromosomes are aligned at equator; spindle fibers are bound to the chromosomes via kinetochores; each chromatid is bound by spindle fiber
anaphase
sister chromatids separate and are pulled toward opposite poles; each chromatid is now chromosomes; nuc envelope still disintegrated; centrosomes and spindle fibers still very visible
middle of anaphase
spindle fibers have bound chromosomes by connecting to kinetochores at their centromeres and are drawing chromosomes apart
separase
degrades cohesin to allow separation of sister chromatids which allows sister chromatids to segregate apart during anaphase
cohesin
hold sister chromatids together at centromere until enzyme separase degrades cohesin (end of metaphase - beginning of anaphase)
dynein
motor protein that pulls the sister chromatids apart; sits on two spindle fibers and pulls on 2 spindle fibers that are connected to chromosomes
telophase
sister chromatids (now chromosomes) have been pulled completely toward 2 poles during anaphase - no movement necessary; chromatin decondenses; nuclear envelope reforms; spindle fibers degenerate to some degree; new cell membrane material is synthesize so 2 daughter cells are now separate functional cells
early mid telophase
nuclear membrane not yet reformed; chromatin still somewhat condensed; cells only beginning to cleave apart, new cell membrane not yet visible
after S phase of interphase
each chromosome contains 2 sister chromatids
number of chromosomes =
number of centromeres; each chromatid is separate molecule of DNA
2 sister chromatids held together at centromere =
one chromosome but 2 DNA molecules
meiosis vs. mitosis
only spermatogonia and oogonia undergo meiosis during M phase other cells undergo mitosis
meiosis
produces 4 haploid daughter cells (one set of chromosome per cell) while mitosis produces 2 diploid daughter cells (2 sets of chromosomes per cell)
recombination
occurs between homologous chromosomes during meiosis which results in child inheriting some chromosomes that contain combination of gene alleles that came down from the grandfather and grandmother
chromosomes doubled in interphase
held together along entire length by protein cohesin; enzyme separase will dissolve cohesin to allow 2 homologous chromosomes to separate during anaphase I and sister chromatids to separate during anaphase II
end of interphase
spindle fiber apparatus (green/yellow) is not yet organized; chromatin is decondensed - no discernable chromosomes in nucleus; nuclear membrane intact
stages of meiosis prophase I and prometaphase I
leptotene, sygotene, pachytene, diplotene, diakinesis; non sister homologous chromatids (one from each member of the homologous chromosome pair) physically cross over at points of contact and exchange material (i.e. homologous recombination occurs)
leptotene
step one of prophase I: chromatin condenses
zygotene
step 2 of prophase I: chromatin condenses homologous chromosomes pair up and engage in synapsis (aligning very close to each other) to produce bivalents aka tetrads
bivalents
2 chromosomes
tetrads
4 chromatids
pachytene
step 3 of prophase I: chromatin condenses synaptonemal complex develops between homologous chromosomes (homologous chromosomes come into contact w each other at one or more place sin each p and q arm)
diplotene
step 4 of prophase I: 2 chromosomes in each bivalent begin to separate but remain joined at the chiasma (i.e. the places where the crossing over took place)
diskinesis
step 5 of prophase I: chromatin condenses further the 2 chromosomes in the bivalent separate farther apart the 2 chromosomes now remain joined only at the ends
early prophase I
centrosomes begin to move toward opposite poles of dividing cell; chromosomes begin to condense
last prophase I (prometaphase I)
centrosomes have migrated to the poles; chromosomes now condensed; nuclear membrane has disappeared; spindle fibers are reaching in to bind chromosomes
homologous recombination in prometaphase I
original chromosome pair in spermatogonium or oogonium; chromosomes double 2 of the 4 chromatids cross over; recombination occur 2 chromatids exchange portions; after 2 cell divison gametes w non recombinant chromosomes and gametes w recombinant chromosome
metaphase I
bivalents are aligned in tetrads along equatorial plane; spindle fibers connect to chromosomes by the kinetochores at their centromeres; cell checks to be sure every chromatid is bound by spindle fiber
late metaphase I
chromosomes are aligned at the equator; spindle fibers are binding the chromosomes
anaphase I
enzyme separase degrades cohesin that hold 2 homologs together but leaves cohesin that is holding sister chromatids together at the centromere intact; 2 chromosomes in each bivalent migrate apart from each other toward opposite poles of diving cell
middle of anaphase I
spindle fibers draw chromosomes apart
protein shugoshin
prevent separation of sister chromatids; protects cohesin at centromeres only from degradation by separase this holds sister chromatids together at centromeres during anaphase I of meiosis so they don’t separate until anaphase II; shugoshin must be degraded during metaphase II so sister chromatids can separate during anaphase II
telophase I
chromosomes have migrate completely to opposite poles; cytokinesis
early-mid telophase
nuclear membrane has not yet reformed; chromatin is still somewhat condensed; cells only begin to cleave apart new cell membrane is not yet visible
interkinesis
nuclear membrane reforms spindle fibers degenerate chromatin decondenses; several proteins are necessary for chromatin condensation in prophase II get phosphorylated and assembled into complexes including some of the cohesins (there are several version of cohesin) and condensin II
reduction division
first cell division; reduces number of chromosomes in cell by half
equational division
second cell division; no change in the number of chromosomes per cell
prophase II
chromatin condenses nuclear envelope degenerates spindle fibers form
metaphase II
chromosomes align at equatorial plane and spindle fibers connect to chromosomes (at kinetochore at the centromere); half the chromatids are recombinant chromatids and half are nonrecombinant chromatids
anaphase II
sister chromatids migrate apart from each other toward opposite poles of the diving cell
telophase II
nuclear membrane reforms, spindle fibers disappear, chromatin decondenses
products of meiosis
chromatin is now decondensed; if chromosomes are drawn as they would appear if they recondensed you can see how half your gametes contain nonrecombinant chromosome from that pair and the other half contain recombinant chromosomes
genetic diversity
maintained by meiosis - recombination creates new gene allele combinations on chromosomes
gene conversion
occurs when the sequence of one allele of a gene is changed and actually becomes the sequence of other allele
heteroduplex DNA
strand from one homolog bound to a strand from the other homolog at the end of recombination
homologous recombination & gene conversion model one
(1) single strand break in each homolog broken ends join w broken ends of other homolog (2) strands that reached across and connected w strand from other homolog now return to original place Holliday junction moves down chromosome (no DNA synthesis necessary)
homologous recombination & gene conversion model two
(1) double strand break in one homolog some nucleotides are removed from each strand (2) one strand of each homolog is used as template to synthesize DNA to fill gap in strand from the other homolog
heterozygous gene & heteroduplex
bubble in heteroduplex DNA bc there will be places where the bases are not complementary to each other and will not bond to each other; DNA repair proteins recognize bubbles like these as things that need to be repaired = cut mismatched bases out of one of DNA strands then use remaining strand as template to synthesize new DNA; for each mismatch it is equally likely that the red strand or blue strand will be cut out
spermatogenesis
produces 4 viable sperm
oogenesis
produces one viable egg
spermatogenesis & oogenesis
right after fertilization zygote/embryo undergoes several rounds of cleavage & cell division w no replication of cytoplasm & organelles; sperm has donated only its DNA and centrosome so all cytoplasm and organelle that are available to be divided among newly created cells come from the egg; when cell divides all cytoplasm and organelles migrate into one daughter cell; cell that gets the cytoplasm and organelles becomes egg other daughter cell is polar body - usually dies off
divisions of oogenesis
1st meiotic divison = 2ndary oocyte and 1st polar body (both haploid each chromosome has 2 chromatids); 2nd meiotic division creates ovum and 2nd polar body (both are haploid; each chromosome contains one chromatid)
time course of sperm
men make sperm at puberty and make them continuously for a variable time period
time course for oogenesis
primary oocytes begin meiosis from 7 months gestation to shortly after birth but they stop at diplotene; meiosis resumes at puberty but only a handful of primary oocytes resume meiosis each month and they stop in metaphase II; meiosis finishes after fertilization occurs
