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 Cell defenses and the sunshine vitamin. Scientific American. 297: Egger, G. et al., Epigenetics in human disease and prospects for epigenetic therapy. Nature. 429: Jaenisch, R. and A. Bird Epigenetic regulation of gene expression: how the genome integrates intrinsic and environmental signals. Nature Genetics Suppl. 33: