BIO 105 1st Edition Lecture 8 Cell Division Lecture Outline I II III Be able to identify Mitosis and Meiosis and its characteristics Know the different phases of the cell cycle Know the characteristics of cancer cells Division Mechanisms Eukaryotic Organisms o Mitosis o Meiosis Prokaryotic Organisms o Fission Cell growth and Division Each minute the human body needs to make about 300 million new cells Purposes of Cell Division o Cell Reproduction Differentiation development of from fertilized egg or zygote o Cell Enlargement need new cells to make more skin bone muscle tissue etc o Cell Repair to repair and replace worn out and used up cells Cell Types Somatic Cells divided by mitosis body cells chromosome number is diploid 2n two of each type of chromosome o Results of Mitosis 1 Two daughter cells 2 With same chromosome number as parent cell 3 Cells identical to parent cells Germ Cells divided by meiosis reproductive cells eggs and sperm chromosome number is haploid n half the number of chromosomes one of each chromosome type o Gametes egg and sperm are produced only in gonads ovaries and testes Each eukaryotic species has characteristic number of chromosomeso Human Somatic Cells 46 Chromosomes 23 pairs one each from mom and dad o Human Gametes sperm eggs have 23 half Human Basics We inherited 23 chromosomes from each parent and we end up with a total of 46 chromosomes 23 pairs Phase one interphase Usually the longest part of the cycle 90 of the cell cycle Cell increases in mass doing its work repair and preparing materials to divide Number of cell components and organelles doubles for division DNA is duplicated Interphase During interphase cells may appear to be inactive but they are not o Preparatory Stage cells are NOT dividing o Centrioles are formed Cytoplasmic Division Usually occurs between late anaphase and end of telophase Two Mechanisms o Cell plate formation plants o Cleavage animals Asexual Reproduction Single parent produces offspring All offspring are genetically identical to one another and to parent Meiosis Two Divisions Two consecutive nuclear divisions o Meiosis I the first division separates homologous chromosomes o Meiosis II the second division separates sister chromatids DNA is copied ONCE but Cell divides TWICE DNA is NOT duplicated between divisions End up with 4 different haploid cells Comparison of Mitosis and Meiosis Mitosis Meiosis DNA replication occurs only once prior DNA replication occurs only once prior Requires only 1 division Requires 2 divisions Produces 2 daughter cells Produces 4 daughter cells Daughter cells are diploid 2n Daughter cells are haploid 1n Daughter cells are genetically identical to Daughter cells are genetically variable parent cells different from parents Fertilization Male and female gametes sperm and egg unite and nuclei fuse Fusion of two haploid nuclei produces diploid nucleus in zygote Which of the two gametes unite is random adds to variation among offspring Factors Contributing to Variation among Offspring why we look different from parents 1 Crossing over during Prophase I 2 Random alignment of chromosomes at Metaphase I 3 Random combination of gametes at fertilization which egg fuses with which sperm Cancer Cells No cell cycle controls Cancer cells do not stop dividing when growth factors are depleted they may o Manufacture their own growth factors o Have abnormality in signaling pathway o Have problem in cell cycle control system Cancer cell may divide indefinitely it they have a continual supply of nutrients o In contrast nearly all mammalian cells divide 20 to 50 times under culture conditions before they stop age and die The abnormal behavior of cancer cells begin when a single cell in a tissue undergoes a transformation that converts it from a normal cell to a cancer cell Tumor a mass of abnormal cells Benign tumor abnormal cell remains at the originating site