1.2 Eukaryotic Cell Growth and the Cell Cycle

Two Stages: INTERPHASE – G 1, S, G 2 MITOSIS (incl. CYTOKINESIS) 1.2 Cell Growth and the 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 PROPHASE Chromosomes 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 PROMETAPHASE The nuclear membrane dissolves, marking the beginning of prometaphase. The chromosomes attach to spindle fibres and begin moving.

MITOSIS METAPHASE Spindle fibres align the chromosomes along the middle of the cell nucleus - metaphase plate.

MITOSIS ANAPHASE Spindle fibre contracts, separating the chromatids, moving them to opposite poles of the cell.

MITOSIS TELOPHASE New 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 bio/activities/cell_cycle/01m.html - classifying stages of mitosis bio/activities/cell_cycle/01m.html bio.cornell.edu/BioG101_104/tut orials/cell_division/CDCK/cdck.html bio.cornell.edu/BioG101_104/tut orials/cell_division/CDCK/cdck.html Cell division construction kit html - htm

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 ell_cycle/cells.html - clear and at the level required. ell_cycle/cells.html cell_cycle/01m.html - classifying stages of mitosis cell_cycle/01m.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 Cycle G1 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.