Mitosis chapter 10

Cell Growth and Reproduction

Sec. 10-1, 10-2, 10-3

There is a limit on how big cells can grow. DNA in the nucleus cannot handle the demand of a large cell. Materials cannot be exchanged efficiently. Smaller cells have a larger surface area to volume ratio, therefore cells reach a certain size and undergo cell division. Before cell division, the cell replicates its DNA.

Chromosomes

Chromosomes are not visible in the cell except during cell division.

At the beginning of cell division the DNA materials condense into a chromosome. Each chromosome is copied and then consists of 2 sister chromatids. The chromatids are attached at a centromere.

Cell Cycle

The cell spends most of its life growing in a step called interphase (part of the cell cycle).

Interphase

          G1 phase cells increase in size and create organelles

          S phase chromosomes are duplicated  

G2 phase organelles and molecules required for cell division   created

          Mitosis starts when all the chromosomes are replicated and conditions are right to make 2 new cells.

Prophase

-longest of the stages of mitosis

-Centrioles form near the nuclear envelope and move toward opposite poles.

-Centrioles, lying in the region called centrosome, organize the spindle fibers.

-Condensed chromosomal material attaches to the spindle fibers via the centromere.

Metaphase

-Chromosomes line up at the middle of the cell.

Anaphase

-Sister chromosomes split at the centromere and migrate toward opposite poles.

Telophase

 -chromosomal material begins to disorganize, nuclear envelope from around it, spindle fibers disappear

-mitosis is complete.

Cytokinesis

-in animals, the cell membrane pinches in the middle and forms 2 new cells

-in plants, cell plate forms between the 2 nuclei, eventually cell membrane and cell wall develop

Cell division is regulated by proteins called cyclins. There are internal and external regulators (proteins) that regulate the cell cycle.