FtsZ filamenting temperature-sensitive mutant Z; protein that is
important in cell division (binary fission), assembles a ring at
the future septum site, prokaryotic homologue to the protein
tubulin (main component of microtubules) in eukaryotes.
G1 cell prepares to divide; may accumulate molecular changes
(e.g. produce more proteins) that cause it to advance through
the rest of the cycle. Once finished, cells reach a restriction
point and are committed to a pathway that leads to cell
division. Past this point, cells advance to the S phase.
S synthesis phase in which the chromosomes are replicated,
chromosomes are now chromatids (or monad), joined to each
other at the centromere region (bound to kinetochore proteins),
to form a pair of sister chromatids (or dyad).
G2 cell accumulates the materials necessary for nuclear and cell
division, preventing cells with damaged DNA from undergoing
mitosis, checked at checkpoint G2/M, with the acting
mechanisms during the checkpoint converging on the inhibition
of the mitotic complex CDK1-cyclin B.
MTOCs microtubule-organizing centres, structures found in eukaryotic
cells from which microtubules grow. In animal cells, the spindle
apparatus is formed from two MTOCs called centrosomes
(each located at a spindle pole, each containing two right-
angles centrioles). Types of microtubules in spindle apparatus:
1. Astral microtubules
Emanate outward from the centrosome toward the plasma
membrane, important for the positioning of the spindle
apparatus within the cell.
, 2. Polar microtubules
Project toward the chromosomes. Polar microtubules that
overlap with each other play a role in the separation of the
two poles (push the poles away from each other)
3. Kinetochore microtubules
Attach to the kinetochores, protein complexes bound to the
centromeres of chromosomes, pull the chromosomes in.
MITOSIS
Prophase nuclear membrane begins to dissociate into small vesicles and
the nucleus becomes less visible, chromatics are condensed into
compact structures, two centrosomes move apart, spindle
apparatus begins to form.
Prometaphase centrosomes move to opposite ends of the cell, establish
two spindle poles, nuclear membrane is completely
fragmented into vesicles, allowing the spindle fibres to
interact with sister chromatids, kinetochore microtubules
connect to kinetochore proteins, if not: the microtubule
depolymerizes and retracts to the centrosomes, by the
end of this phase the spindle apparatus is fully formed.
Metaphase sister chromatids pairs align themselves along the
metaphase plate, at this point, each pair of chromatids is
attached to both poles by kinetochore microtubules.
Anaphase connection that is responsible for holding the pairs of
sister chromatids together is broken, the two poles (in the
cell) move farther apart due to the elongation of polar
microtubules, which slide in opposite directions (done by
motor proteins).
, Telophase chromosomes reach their respective poles and decondense,
nuclear membrane reforms to produce two separate nuclei.
Cytokinesis shortly after anaphase, a contractile ring (myosin motor
proteins, actin filaments) assembles at the cytoplasmic
surface of the plasma membrane, myosin hydrolyses ATP,
which shortens the ring, thereby constricting the plasma
membrane to form a cleavage furrow that ingresses,
continuing until the cell is divided into two daughter cells.
PROPHASE of MEIOSIS I
Leptotene replicated chromosomes begin to condense and become visible
with a light microscope.
Zygotene synapsis, in which homologous chromosomes recognize each
other and begin to align themselves along their entire lengths
(in most species, this involves the formation of a synaptonemal
complex that forms between the homologous chromosomes).
Pachytene homologs are completely aligned, associated chromatids
or bivalents (tetrad) each contain two pairs of sister
chromatids, crossing-over takes place (multiple times)
and a chiasma is formed.
Diplotene synaptonemal complex has largely disappeared, chromatids
within a bivalent pull apart slightly.
