Cell Cycle

Cell division is the basis of reproduction for every organism. It also replaces worn-out or damaged cells.

CELL CYCLE – an ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division into two cells.

Interphase – most of the cell cycle is spent in interphase.

G1 (gap 1) – cell grows

S (synthesis)– cell continues to grow and copies its chromosomes

G2 (gap 2) – grows some more and completes preparations for division

Mitotic phase (M Phase) – cell acutally divides. Consists of mitosis and cytokinesis.

Interphase-Cell synthesizes new molecules and organelles.

-by G2, the cell has doubled its contents and contains two centrosomes.

-In the nucleus – chromosomes are duplicated but can not be distinguished individually. They are still loose chromatin.

-nucleus contains nucleoli (making ribosomes)

Prophase

NUCLEUS – the chromatin becomes tightly coiled and folded, forming chromosomes that can be seen with a light microscope. Nucleoli disappears.

CHROMOSOMES – each chromosome appears as two identical sister chromatids joined together (centromere)

CYTOPLASM – spindles (microtubules) begin to form – growing out from the centrosomes. Centrosomes move away from each other.

Prometaphase/MetaphasePROMETAPHASE

NUCLEUS – nuclear membrane breaks apart and disappears.

CYTOPLASM – Centrosomes are at opposite poles. Spindle fibers extend out and reach the chromosomes.

CHROMOSOMES – Each chromosome has a kinetochore (at the centromere). Spindle fibers attach to the kinetochore. Spingle fibers move the chromosomes toward the center of cell.

METAPHASE

CHROMOSOMES – the chromosomes convene on the metaphase plate, an imaginary plane equidistant between the two poles.

AnaphaseCHROMOSOMES –

-Centromeres or each chromosome come apart. Sister chromatids are seperated and are considered daughter chromosomes.

-Proteins on the kinetochores (powered by ATP) “walk” the daughter chromosomes (centromere first) along the spindle fiber toward opposite poles.

-spindle fibers attached to chromosomes shorten.

CELL

-cell becomes enlongated.

TelophaseCELL

-elongation continues

NUCLEUS

-daughter nuclei appear at the two poles. Nuclear membranes (envelopes) from around the chromosomes.

-Nucleoli reappear

CHROMOSOMES

-chromatin of the chromosomes uncoils.

CYTOPLASM

-spindles disappear

Cytokinesis“Division of the cytoplasm”

ANIMAL CELL

-occurs by a process called cleavage. The first sign is the appearance of a cleavage furrow (a shallow groove in the cell membrane). Furrow deepens and eventually pinches the parent cell into two.

PLANT CELL

-During telophase, vesicles containing cell wall material collect at the middle of the parent cell. The vesicles fuse together, forming a membrane called the cell plate. Cell plate grows outward. Membrane around the cell plate fuses with the cell membrane and the cell plate’s contents join the parent cell wall.