How Cells Divide

All organisms grow and reproduce and pass on hereditary information from 1 generation to the next

Cell division is necessary for:

growth

healing

cell replacement

reproduction

The process is complex requiring the replication of chromosomes and proper separation into daughter cells

What controls this process is key to understanding the molecular basis of cancer and other diseases.

Bacterial cell division = Binary Fission

• One mother cell divides to form 2 daughter cells• Each daughter cell is a “clone” of the mother cell that

produced it• First, the single chromosome replicates; makes a copy of

itself• As DNA replication completes, the 2 copies of

chromosomes separate to opposite sides of the cell• The cell divides in half with the aid of FtsZ protein that

resembles both tubulin and actin proteins• The Cell Cycle does not operate in prokaryotic cells

The process of

Binary fission

FtsZ protein acts to create a septum between dividing bacteria

Eukaryotic chromosomes

• Number of chromosomes varies; typically between 10 and 50

• Humans have 46 chromosomes (23 pairs of homologous chromosomes)

• Most eukaryotic species are diploid (2N), with haploid (N) gametes

• Composed of chromatin (40% DNA/60% protein)• Chromosomes are packaged within nuclei

around histone proteins

SEM of duplicated human chromosomes just prior to mitosis

Levels of chromosome organization

The life cycle of a eukaryotic cell:the Cell Cycle

• Since eukaryotic cells are fundamentally different than prokaryotic cells as they:– Contain multiple chromosomes– Are many times contained in multi-celled organism

• Therefore:– cell division is controlled– process of duplicating (replicating) chromosomes is

controlled

General diagram of the Cell Cycle

The Cell Cycle is divided into 5 phases

• G1 = Gap phase 1 –• S = Synthesis phase• G2 = Gap phase 2• M = mitosis• C = cytokinesis

Articles for Review #4

Tavera-Mendoza, L.E. and J.H. White. 2007. Cell defenses and the sunshine vitamin. Scientific American. 297: 62-72.

Egger, G. et al., 2004. Epigenetics in human disease and prospects for epigenetic therapy. Nature. 429: 457-461.

Jaenisch, R. and A. Bird. 2003. Epigenetic regulation of gene expression: how the genome integrates intrinsic and environmental signals. Nature Genetics Suppl. 33: 245-251.