BIO 105 1st Edition Lecture 8Cell DivisionLecture Outline:I. Be able to identify Mitosis and Meiosis and its’ characteristicsII. Know the different phases of the cell cycleIII. Know the characteristics of cancer cells Division Mechanisms- Eukaryotic Organismso Mitosiso Meiosis- Prokaryotic Organismso 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 zygoteo 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 chromosomeo Results of Mitosis1. Two daughter cells2. With same chromosome number as parent cell3. 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 typeo Gametes (egg and sperm) are produced only in gonads (ovaries and testes)- Each eukaryotic species has characteristic number of chromosomes-o 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 noto Preparatory Stage- cells are NOT dividingo Centrioles are formed Cytoplasmic Division- Usually occurs between late anaphase and end of telophase- Two Mechanismso 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 divisionso Meiosis I- the first division- separates homologous chromosomeso 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 MeiosisMitosis MeiosisDNA replication occurs only once prior DNA replication occurs only once priorRequires only 1 division Requires 2 divisionsProduces 2 daughter cells Produces 4 daughter cellsDaughter cells are diploid (2n) Daughter cells are haploid (1n)Daughter cells are genetically identical to parent cellsDaughter cells are genetically variable (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 parents1. Crossing over during Prophase I2. 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 mayo Manufacture their own growth factorso Have abnormality in signaling pathwayo Have problem in cell cycle control system- Cancer cell may divide indefinitely it they have a continual supply of nutrientso 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