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Mitosis and Meiosis. The continuity of life is based on the reproduction of cells, or cell division. Cell Reproduction. Two types of cell division in eukaryotic cells: one called mitosis and the other meiosis Cell division in prokaryotic (bacteria) cells: is called binary fission
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Mitosis and Meiosis The continuity of life is based on the reproduction of cells, or cell division.
Cell Reproduction • Two types of cell division in eukaryotic cells: one called mitosis and the other meiosis • Cell division in prokaryotic (bacteria) cells: is called binary fission • Words of Wisdom: Understand the process, and you will understand the words.
Key Ideas • Question: Why do cells divide? • Question: How do cells divide?
Why don’t cells get giant? • Remember cell membranes? • Input of nutrients and gets rid of wastes. • Think about Geometry…volume of a cube is going to increase faster than the surface area. The cell membrane is a surface area issue.
Dividing a Eukaryotic Cell • Example: skin cell Skin cell A skin cell will divide to form two skin cells. The genetic information must be the same. • Before a cell can divide, its genetic information must be organized and it must be doubled.
Organizing Genetic Material • DNA • Chromatin – DNA wrapped around histone proteins (help maintain the shape of chromosome and aid in the tight packing of DNA) • Continues coiling • Chromosome – 2 molecules of DNA
Understanding Chromosomes • FYI: • Chromosomes only exist during cell division • The DNA has doubled by replicating itself
How Are Chromosomes Categorized? • Sex chromosomes – c`somes that determine the sex of an organism. For example in humans X female Y Male. Normal females have two X c`somes and normal males have an X and a Y c`some. • Autosomes – all the other c`somes. For example in humans 44 c`somes are autosomes and 2 are sex c`somes. Total of 46 c`somes.
Homologous Chromosomes • Homologous chromosome – two copies of each autosome produced by sexual reproduction • Same size, same shape • For example, if one c`some in a pair of homologous c`somes contains a gene for eye color so will the other c`some in the homologous pair.
Karyotype • Karyotype – a photomicrograph of the c`somes in a dividing cell found in a normal human. • Used to examine an individuals c`somes. • Made by sampling a person’s blood. • White blood cells from the sample are treated with chemicals to stimulate mitosis.
Diploid and Haploid Cells • Diploid – cells having two sets of c`somes. Have both autosomes (homologous c`somes) and sex c`somes. • All normal human cells, except reproductive cells (sperm and egg cells) are diploid cells. • Abbreviated as 2n • Haploid – human sperm and egg cells. Contain only one set of c`somes. They have half the number of c`somes that are present in diploid cells. • Human haploid cells have only one c`some of each homologous pair and only one sex c`some. • Abbreviated as 1n • When a sperm cell (1n) and an egg cell (1n) combine to create the first cell of a new organism, the new cell will be diploid (2n).
Key Ideas Answered • Question: Why do cells divide? • Answer: To maintain their volume to surface ratio. • Question: How do cells divide? • Answer: 1. The cell organizes its genetic information and doubles it. • Chromosomes are formed by DNA packing around histone proteins • This period of the cell cycle is called Interphase where the: • Cell grows, DNA replicates, and cell prepares to divide
Examining the Eukaryotic Cell Cycle • 90% of a cell’s life is spent in Interphase! • Interphase Divided into three phases: G1 Phase – where cells function, cell grows in size S Phase – DNA is replicated G2 Phase – where a cell can grow some more before it divides • A cell spends only 10% of it’s life dividing! Some never divide! • Onward to Cell Division!!!
