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