15. Cell cycle, mitosis, meiosis, mechanics of cell division Flashcards
cell cycle, meiosi
cell cycle
The life of eukaryotic cells, which lasts from the formation of the cell to the next cell division.
It can be divided into two phases, the resting period and the subsequent cell division (M-phase).
The resting period can be further divided into three phases: first growth phase (G1), synthesis
phase (S), second growth phase (G2).
meiosis
Cell division which reduces the number of chromosomes. The number of chromosomes of the
4 progeny cells is half of the number in the parent cell, and their genetic constitution is a mixture
of the parents. Meiosis consists of two divisions, the first (after crossing over) separates the
homologous chromosomes, while the second splits the sister chromatids of each chromosome.
interphase, mitosis
interphase – and its subphases
A period NOT containing the M-phase of the cell cycle of proliferative cells, which can be
divided into further parts: G1 phase is the growing stage of the cell; S phase is the part of DNA
and histone synthesis, and G2 phase localized directly before mitosis, in which direct
preparatory processes occur to the mitosis.
mitosis, karyiokinesis – and its subphases
Nuclear division, within the M-phase of cell cycle in proliferating cells, which produces two
nuclei with type and number of choromosomes identical to the parent cell. It can be divided
into further subphases based on their specific biochemical and morphological happenings:
prophase, prometaphase, metaphase, anaphase and telophase.
mtoc , centriolo cycle
MTOC (centrosome)
It is composed of 2 centrioles and the pericentriolar material which surrounds them. The
gamma-tubulin rings embedded into the pericentriolar material are the nucleation sites of
microtubules. In interphase cells there is one centrosome which in proliferating cells localizes
either near the nucleus and - in terminally differentiated cells - at the membrane, where (the
mother centriolum) nucleates the formation of the primary cilium.
centriole cycle
Centrioles of the centrosome are duplicated in a semiconservative manner. In the S-phase of
the cell cycle the two centrioles localized in the centrosome separate and move away from each
other, and a new, daughter centriole starts to bud at right angle from both of them. These
daughter centrioles reach their final size at the end of G2 phase. In the prophase of mitosis the
thus formed two centrosomes migrate toward the opposite poles of the cell and organize the
formation of the mitotic spindle. All this can occur also in enucleated cells and also under the
arrest of DNA synthesis
kinetocore, mitoci spindle
kinetochore
It is the protein structure assembled on the centromere of chromatids where the kinetochore
microtubules of the spindle attach during mitotic and meiotic cell division, to pull the
chromatids apart.
mitotic spindle
It consists of polar (interpolar), kinetochore and astral (unattached) microtubules. These
connect the poles to each other, to the kinetochor of chromosomes, and to submembrane cell
cortex, respectively. Their role is to segregate the chromosomes’ two chromatids equally into
the two daughter cells upon mitosis.
cohesine, securine, separase, cytokines
cohesin, securin, separase
Proteins which play roles in the separation of sister chromatids in the anaphase of mitosis. The
APC is activated directly before the onset of anaphase and ubiquitinates securin, which keeps
the separase in inactive form, so it is degraded in the proteasomes. The activated separase
enzyme degrades the cohesion complexes which keep the sister chromatids together. The
separated sister chromatids are then moved to the two poles of the cell by the spindle.
cytokinesis
The M-phase of the cell cycle can be divided into two overlapping parts, mitosis (more
accurately called karyokinesis) and the division of the cytoplasm (cytokinesis). Cytokinesis
begins in the anaphase B of part of M-phase and ends in the telophase of M-phase.
