The Cell Cycle & Mitosis

“Omnis cellula e cellula.”“Every cell from a cell.”

—Rudolph Virchow, Germany, 1855

Fig. 12-2a

100 µm Reproduction: An amoeba,A single celled eukaryote, divides into two cells. Each new cell will be an individual organism.

Fig. 12-2b

200 µm

Growth and Development: A sand dollar embryo just after the fertilized egg divided.

Fig. 12-2c

20 µm Tissue Renewal: Bone marrow cells form new blood cells.

The Cell Cycle • The life of a cell

from the time it first formed from a dividing parent cell until its own division into two cells.

• Consists of interphase, mitosis & cytokinesis.

Interphase• The cell grows (increases in mass),• Copies cytoplasmic organelles and• Produces proteins• Duplicates chromosomes• 90% of cell cycle is in interphase

MitosisInterphase Prophase Metaphase Anaphase Telophase

Replication Alignment Separation

Fig. 12-6

G2 of InterphaseCentrosomes(with centriolepairs)

Chromatin(duplicated)

Nucleolus Nuclearenvelope

Plasmamembrane

Early mitoticspindle

Aster Centromere

Chromosome, consisting of two sister chromatids

Prophase Prometaphase

Fragmentsof nuclearenvelope

Nonkinetochoremicrotubules

Kinetochore Kinetochoremicrotubule

Metaphase

Metaphaseplate

Spindle Centrosome atone spindle pole

Anaphase

Daughterchromosomes

Telophase and Cytokinesis

Cleavagefurrow

Nucleolusforming

Nuclearenvelopeforming

Replication • DNA replicates during interphase.

The Mitotic Spindle• Spindle fibers

made of microtubules and proteins that controls chromosome movement during mitosis.

• Assembled at centrosome in animal cells (MTOC)

Alignment (Prophase & Metaphase)

• Microtubules extend from centrosomes and some attach to kinetochores on the chromatids

• Microtubles move the chromatids until their centromeres lie on the metaphase plate.

Separation—Anaphase & Telophase

• Kinetochore microtubules shorten and pull the chromatids apart

• The chromosomes are pulled to opposite poles of the cell

In animal cells, cytokinesis occurs by forming a cleavage furrow which deepens until the parent cell is pinched in two.

In plant cells, a cell plate forms in the middle of the cell.