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The cell cycle and cell division
The cell cycle
Interval between cell formation by the division of a mother cell and reproduction—its own division.
In eukaryotic cells
consist of:
– Interphase
– Mitotic
(M)-phase
Interphase
• Comprises about 90% of cell cycle.
• Made up of:
G1-phase – cell growth and preparation for S phase (supply of nucleotides, RNA and protein synthesis)
(G0-phase) – rest phase
S- phase – DNA replication
G2- phase - cell growth and preparation for M-phase (tubulin synthesis)
Chromosome afterS-phase
A chromosome is made up of DNA and histone protein complex called chromatin.
Chromatin is a long, thin fiber that is folded and coiled to form chromosomes.
The regulation of cell cycle
Checkpoints
The cell division
Prokaryotic cells – direct method of division
Eukaryotic cells
• Amitosis (direct method of division)
• Mitosis (indirect method of division)
• Meiosis (reduction division)
Mitosis
– division ofsomatic cells
(karyokinesis):ProphaseMetaphaseAnaphaseTelophase
Cytokinesis
Prophase• chromatin condenses into chromosomes = consist from
2 chromatids (sister chromatids),
• nucleolus disappears
• nucleolar envelope breaks down
• formation of spindle fibers (microtubules)
Late prophase,Prometaphase
Mitosis
A spindle fibers attach centromeres to centrioles by kinetochores.
Metaphase• formation of definitive spindle fibers
• chromatin is in maximum of condensation
• chromosomes move to the equatorial plate (center of cell)
In the end of metaphase centromere starts to disapear.
Mitosis
Anaphase• spindle fibers shorten
• chromatids separate and move apart
After separation, chromatids are considered as chromosomes = cell contains twice as normal chromosomes.
At the end of anaphase – the equal number of chromosomes on the poles.
Mitosis
Telophase
• decondensation of chromosomes at the poles
• reconstruction of nucleolus and nuclear envelope
Mitosis
Cytokinsis
• the division of the cytoplasm
• actin and myosin II contract to generate the force that divides the cytoplasm in two cells = the contractile ring
• Interphase
• Meiosis I
• Cytokinesis
• Interphase
(without S-phase)
• Meiosis II
• Cytokinesis
Meiosis
a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells.
Meiosis I
Stages of Prophase I:
leptotene – condensation of chromosomes
zygotene – pairing homologous chromosomes = bivalent or
tetrad chromosome bound by synaptonemal complex,
pachytene – crossing over (recombination) = nonsister
chromatids of homologous chromosomes exchange segments,
diplotene – degradation of synaptonemal complex,
homologous chromosomes stay connected to
each other by chiasmata,
diakinesis – nucleolus disappear,
the nuclear envelope breaks down.
Meiosis I
Me
iosi
s II
:
The cell death
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