Why Do Cells Divide?

Cell Size Limitations Getting things into cell at an efficient rate Nutrients Water Oxygen Removing things from the cell quickly wastes DNA limits cell size If cell is too big then DNA cannot make enough proteins to support the cell

What limits the size of cells? Surface Area to Volume Ratio - How much space is on the outside (cell membrane) compared to the space on the inside of the cell. As the surface area of something increases, it’s volume increases faster The larger a cell becomes, the less efficient it is Cells that grow too large no longer have enough surface area to take in nutrients and remove waste

Ratio of Surface Area to Volume in Cells Cell Size Surface Area (length x width x 6) 1 cm x 1 cm x 6 = 6 cm2 2 cm x 2 cm x 6 = 24 cm2 3 cm x 3 cm x 6 = 54 cm2 Volume (length x width x height) 1 cm x 1 cm x 1 cm = 1 cm3 2 cm x 2 cm x 2 cm = 8 cm3 3 cm x 3 cm x 3 cm = 27 cm3 Ratio of Surface Area to Volume 6 / 1 = 6 : 1 24 / 8 = 3 : 1 54 / 27 = 2 : 1 The volume of the cell increases faster than its surface area How does a cell most efficiently move material without getting too big?? It divides!!

Cells get old and worn out Another reason to divide – replace old parts Just like anything else, cells get worn out. They need repair, and, just like an old car, eventually need replacement. The best way to fix what ails a cell is to replace that cell all together.

What does a cell need to do first? In order to reproduce, a cell must make copies of its DNA and organelles. The new cell needs all the stuff the old cell has.

DNA DNA must be copied in a process called DNA replication. After replication, the DNA is all stringy and tangled (called chromatin), but must be separated into a new cell. Before this can happen, the DNA must coil up into chromosomes.

Chromosomes Threadlike structures made up of DNA that coil around proteins called histones. Contains genetic information that is passed form parents to offspring. chromosomes Genes (DNA)

Chromatids One of two identical parts of a duplicated chromosome The two identical chromatids are known as sister chromatids and are held together at a central point called the centromere Centromere Sister chromatids

Number of Chromosomes Fruit Flies: 8 Carrots: 20 Turkey: 82 White Ash: 138 Fern: 480 Humans: 46 http://i.pbase.com/u9/dannysmythe/large/4319077.Carrot.jpg http://www.news.wisc.edu/newsphotos/images/fruit_fly_research03_6801.JPG

Soma – what? The 46 human chromosomes are found in most human cells These cells are called somatic cells AKA body cells Some cells in the body only have 23 chromosomes These are called gametes 2 types: eggs and sperm

Karyotype Visual representation of the chromosomes in a cell HUMAN CHROMOSOMES

Genetic Abnormalities

The Cell Cycle © Pearson Education, Inc.