Cell Division Chapter 8 http://www.youtube.com/watch?v=Q6ucKWIIFmg

Cell Division Doubling organelles and proteins DNA replication Nuclear division Cytoplasmic division

Cell Increase and Decrease Maintain homeostasis Cell numbers kept in check by this mechanism Through cell division of somatic cells and cell death Cell division – interphase, mitosis and cytokinesis Cell death – apoptosis

Cell Increase and Decrease Somatic cells Asexual reproduction increase in number of somatic cells Increase in number unicellular organisms Germ cells Sexual reproduction requires the production of eggs and sperm

Chromosomes

Mitosis verse Meiosis?? Mitosis Meiosis Division of somatic cell nuclei Meiosis Division of gamete nuclei

Cell Cycle – Somatic cells Set of stages that involves cell growth and nuclear division Consists of: Interphase G1 S G2 Meiotic stage Mitosis and Cytokinesis http://www.cellsalive.com/cell_cycle.htm

Interphase When the cell carries on its usual functions Main stages: Gap before DNA synthesis begins S Time when DNA duplicated*************** G2 Gap between time DNA duplication ends and mitosis begins

Interphase in Meiosis? Meiosis is a "one-way" process Cannot be said to engage in a cell cycle as mitosis does Preparatory steps that lead up to meiosis are identical in pattern and name to the interphase of the mitotic cell cycle

Cytokinesis in Animal Cells Cytoplasmic cleavage Accompanies mitosis Separate process Cleavage furrow forms between daughter nuclei Contractile ring contracts deepening the furrow Continues until separation is complete

Human DNA in somatic cells 22-23 pairs of homologous chromosomes Difference? Autosomes (1-22) Sex chromosomes (23) Somatic cells have 46 chromosomes Diploid 2n

Human DNA in gametes Due to reductional division Halves the diploid number (2n) to a haploid number (n) 23 total chromosomes

DNA Replication Duplicated chromosome Sister chromatids Composed of 2 sister chromatids held together by a centromere Sister chromatids Genetically identical When separate, each daughter nucleus gets a chromosome DNA copied DNA divided

Division of the Nucleus Nucleus must be divided Parent cell’s DNA into 2 nuclei 2 ways nucleus can divide: Mitosis Meiosis

Maintaining the Chromosome Number Mitosis Maintaining the Chromosome Number

Mitosis Mitosis 4 main stages: Prophase Metaphase Anaphase Telophase

The Cell Cycle 1. Prophase – Mitosis begins! Threadlike form Spindle fibers appear DNA start to condense Aster formed Nuclear envelope starts to break apart Centrioles move to opposite sides of the cell

The Cell Cycle 2. Metaphase Duplicated chromosomes aligned midway between the poles Associated with spindle fibers

The Cell Cycle 3. Anaphase Sister chromatids separate from each other and move to opposite poles Become daughter chromosomes

The Cell Cycle 4. Telophase Return to threadlike form as in prophase New nuclear envelope separates each chromosome cluster 2 new nuclei!!!!! http://www.cellsalive.com/mitosis.htm

Reducing the Chromosome Number Meiosis Reducing the Chromosome Number

Meiosis Mechanism for dividing the nucleus of germ cells Oogonia and spermatogonia 2n Meiosis must take place prior to formation of gametes Sperm and eggs n First stage in sexual reproduction

Meiosis Overview Occurs in the life cycle of sexually reproducing organisms Reduces the chromosome number 2 divisions, 4 daughter cells Cells are diploid at beginning of meiosis TWO consecutive divisions Result is 4 haploid nuclei Divided into: Meiosis I Meiosis II

Comparisons between males and females Spermatogenesis Begins at puberty and continues throughout life Oogenesis Begins in the fetus Primary oocytes are arrested in prophase I At puberty, one primary oocyte continues the process of meiosis during each menstrual cycle

Reducing the Chromosome Number Genetic Recombination Promotes genetic variability Occurs in Two Ways Crossing Over Independent Assortment of paired chromosomes

How Plant Cells Divide Occurs in meristematic tissues Same phases as animal cells Plant cells do not have centrioles or asters 27

Plant Cells

Cytokinesis in Plant Cells Flattened, small disk appears between daughter cells Golgi apparatus produces vesicles which move to disk Release molecules which build new cell walls Vesicle membranes complete plasma membranes 29

Cell Division in Prokaryotes Binary Fission Prokaryotes have a single chromosome Chromosomal replication occurs before division Cell elongates to twice its length Cell membrane grows inward until division is complete 30

Comparisons Mitosis Meiosis DNA replication occurs only once Requires only one division Produces two daughter cells Diploid daughter cells 2n Genetically identical cells produced Occurs all the time Meiosis DNA replication occurs only once Requires two divisions Produces four daughter cells Haploid daughter cells n Genetically variable cells produced Occurs only at certain times

Comparisons

Overview of the Life Cycle of Humans

Mitosis and Meiosis Gone Awry Cancer Chromosomal Abnormalities

Cancer disease of the cell cycle Cancer cells do not respond normally to the cell cycle control system can form tumors if malignant, can spread to other parts of the body

Important Terms Tumor Benign Malignant Metastasis Cancer Carcinoma Sarcoma Lymphoma

Cancer Treatment Cancer treatment can involve Radiation therapy which damages DNA and disrupts cell division Chemotherapy which uses drugs that disrupt cell division

Chromosomal Abnormalities Nondisjunction members of a chromosome pair fail to separate during anaphase produces gametes with an incorrect number of chromosomes If normal sperm fertilizes an egg with an extra chromosome result is a zygote with a total of 2n + 1 chromosomes

Chromosomal Abnormalities Down Syndrome: Trisomy 21 condition in which an individual has an extra chromosome 21 Affects about one out of every 700 children

Chromosomal Abnormalities Nondisjunction can also affect the sex chromosomes Klinefelter's Syndrome XXY males Turner Syndrome XO female