1.2 Eukaryotic Cell Growth andthe Cell Cycle

Two Stages:

INTERPHASE – G1, S, G2

MITOSIS (incl. CYTOKINESIS)

1.2 Cell Growth andthe Cell Cycle

INTERPHASE

The cell is preparing for mitosis.

Chromosomes are not clearly visible in the nucleus.

Nuclear membrane intact.

When complete cell is ready for mitosis

MITOSIS

PROPHASEChromosomes condense, become visible.

Nucleolus disappears.

Centrioles start to migrate to opposite ends of cell

Fibres extend from centrioles across the cell to form the mitotic spindle (made of microtubules).

Chromosomes start to condense and appear

MITOSIS

PROMETAPHASEThe nuclear membrane dissolves, marking the beginning of prometaphase.

The chromosomes attach to spindle fibres and begin moving.

MITOSIS

METAPHASESpindle fibres align the chromosomes along the middle of the cell nucleus - metaphase plate.

MITOSIS

ANAPHASESpindle fibre contracts, separating the chromatids, moving them to opposite poles of the cell.

MITOSIS

TELOPHASENew membranes form around the daughter nuclei.

The chromosomes disperse and are no longer visible, nucleoli reappear

The spindle fibres disperse

Cytokinesis or the partitioning of the cell may also begin during this stage.

Mitosis Practice sheets

http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/01m.html - classifying stages of mitosis

http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/cell_division/CDCK/cdck.html

Cell division construction kit http://www.cellsalive.com/

cell_cycle.html -

CYTOKINESIS

In animal cells,

Ring of actin around centre of cell contracts, pinching the cell into two daughter cells, each with one nucleus.

In plant cells,

A cell plate is synthesized between the two daughter cells as the cell wall extends, the cell membrane is laid down on either side of it.

Web pages

http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells.html - clear and at the level required.

http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/01m.html - classifying stages of mitosis

http://www.cellsalive.com/cell_cycle.html -

The nucleus - membrane bound organelle that contains the genetic information in the form of chromatin, highly folded ribbon-like complexes of DNA and a class of proteins called histones.

When a cell divides, chromatin fibers are very highly folded, and become visible in the light microscope as chromosomes. During interphase (between divisions), chromatin is more extended, a form used for expression genetic information.

The DNA of chromatin is wrapped around a complex of histones making what can appear in the electron microscope as "beads on a string" or nucleosomes. It is the packaging of these nucleosomes which is responsible for condensing of chromsosomes during the first stage of mitosis (prophase).

Cell CycleG1 stage stands for "GAP 1".

The S stage stands for "Synthesis, when DNA replication occurs.

G2 stage stands for "GAP 2“

M stage stands for "mitosis", and is when nuclear (chromosomes separate) and cytoplasmic (cytokinesis) division occur.