1. Cell Division
Mitosis

2. Think About This All living organisms age……
What changes are occurring when organisms live?

3. In the case of multicellular organisms, as organisms age, they grow more and more cells.
When they begin dying, they lose more and more cells.
The process whereby cells divide is called cell division.
It is important to remember that cells do not grow infinitely larger in size as organisms grow but they grow larger in number.

4. Limits of Cell Growth
Organisms are limited in size by their surface area to volume ratio.
If cells are too large, they would have too difficult of a time transporting materials in and out of the cell.

5. Why do cells divide?
Reproduction
Growth
Repair

6. From One Cell to Trillions of Cells

7. The Cell’s Genome
The cell’s entire hereditary endowment of DNA is called its genome.
A cell must replicate and distribute an identical copy of its genome to each one of its daughter cells.
A typical human cell has about 3 meters of DNA- a length about 300,000 times greater than the cell’s diameter.

8. Chromosomes
Each chromosome is made out of tightly packed chromatin fiber.
Chromatin is made out of complexes called nucleosomes which are DNA strands coiled around histone proteins.
Humans have 23 pairs or 46 chromosomes in each somatic cell (all cells excluding gametes).

9. Chromosome Structure
Each chromosome is composed of a centromere and chromatids.
After DNA replication, there are two sister chromatids.
Sister chromatids are pulled apart during mitosis, one going into each daughter cell.

10. DNA
core of
histone
One nucleosome
Fig. 8.3, p. 129

11. one chromosome (unduplicated)
one chromatid
two sister
chromatids
one chromatid
one chromosome (duplicated)
Fig. 8.2, p. 128

12. Chromosomes