Agricultural Biotechnology Agri 06 Lecture Notes PDF

UNIVERSITY OF SOUTHERN MINDANAO Agricultural Biotechnology Agri 06 College of Agriculture  Lecture 2 The Foundation and Blueprint of Life Objectives After finishing this lecture, you should be able to: Explain why cells are the foundation of life;...

UNIVERSITY OF SOUTHERN MINDANAO Agricultural Biotechnology Agri 06 College of Agriculture  Lecture 2 The Foundation and Blueprint of Life Objectives After finishing this lecture, you should be able to: Explain why cells are the foundation of life; Compare prokaryotic and eukaryotic cell; Compare mitosis and meiosis; Compare DNA and RNA; Explain the central dogma of molecular biology Predict outcomes of monohybrid and dihybrid crosses  Cells are the foundation of life All the processes involving growth, reproduction, and maintaining the well-being of the organism happen at the cellular level All living organisms come from previously existing cell Allows the continuity of life and the transfer of genetic materials from one generation to another  Cells have chemical components Inorganic molecules water mineral ions Organic molecules nucleic acids carbohydrate proteins lipids  The organic components in cells Nucleic Acids – repeats of nucleotides Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) Polysaccharides (complex carbohydrates) – polymers of glucose Monosaccharides- glucose, fructose, ribose Dissaccharides – sucrose, lactose Polysaccharides-carbohydrates Proteins- polymers of amino acids Fats/lipids- polymers of fatty acids There are two basic types of cells  Plant and animal cells are eukaryotic cells Animal cell Plant cell Cells of a complex organism vary in structure and function Human nerve cell Red blood cell Sperm cell Eukaryotic cells undergo the cell cycle 1. Interphase G1- prepares for chromosome replication. S - DNA replicates and new chromosomes (sister chromatids) are formed. G2 - Cell prepares for mitosis and cell division. 2. Mitotic phase – cell nuclear division The cell cycle is divided into two major phases: Interphase Mitotic phase (M- Phase) All cellular components are duplicated during interphase before cell division Interphase S G1 G2 Mitotic phase  Chromosomes are cellular components found inside the cell nucleus Key features of the chromosome are: Centromere – central constricted region Arms (chromatids) Telomeres - special structures at the ends  homologous chromosomes contain DNA that codes for the same genes. Chromosomes occur in pairs in most animals and crops  Animal and crop species differ in the number of chromosome pairs Species Chromosome Species Chromosome pairs pairs Man 23 Rice 12 Cattle 30 Corn 10 Horse 32 Soybean 20 Pig 19 Tomato 12 Sheep 27 Watermelon 11 Goat 30 Sugar beet 9 Chicken 39 Cassava 18 Duck 40 Barley 12  1a 1b Chromosome duplication occurs during the S phase of interphase 1a 1b 1a 1b 1a 1b The mitotic or mitosis phase occurs in somatic cells Somatic cells - are any cell of a living organism other than the reproductive cells Examples: Root cells, stem cells, leaf cells Muscle cells, neurons, red blood cells, skin cells Mitosis has four distinct stages Prophase Metaphase Telophase Anaphase  Prophase Chromosomes shorten, thicken, and become visible by light microscopy. Centrioles move apart and mitotic spindle begins to form. Centrioles migrate to opposite sides of nucleus and nuclear envelope begins to disappear.  Metaphase Nuclear envelope disappears completely. Replicated chromosomes held together at the centromere are aligned on equator of the spindle (metaphase plate).  Anaphase Centromeres split and daughter chromosomes migrate to opposite poles. Cell division (cytokinesis) begins.  Nuclear envelopes Telophase reform, chromosomes become extended and less visible, and cell division continues. Cytokinesis is the cytoplasmic division that occur after mitosis: animal vs plant cells The duration of mitosis in living cells vary (Burns, 1983) Mitosis in onion root tips  Some key points to remember Mitosis ultimately produces two daughter cells genetically identical to the mother cell Barring rare mutations Processes requiring mitotic cell division Development of multicellularity Organismal growth Wound repair Tissue regeneration  Meiosis is a type of cell nuclear division that produces the sex cells or gametes Spermatogenesis - the process by which sperm cell production occurs; Oogenesis - the differentiation of the ovum (egg cell) into a cell competent to further develop when fertilized  Gametes contain one set of chromosomes that combine during fertilization Gametes are produced from diploid cells through meiosis Gametes are haploid cells with half the number of chromosomes Fertilization restores the number of chromosomes  Haploid cells contain only one set of Chromosomes (n).  Haploid cells are formed by the process of meiosis.  Diploid, as the name indicates, contains two sets of chromosomes (2n).  Diploid cells undergo mitosis.  Meiosis is more complex than mitosis Meiosis begins after a cell has progressed through G1, S, & G2 Meiosis involves two successive divisions Meiosis I Prophase I Leptotene Zygotene Metaphase I Pachytene Anaphase I Diplotene Telophase I Diakinesis Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I Prophase I Similar to prophase of mitosis, except that homologous chromosomes pair and cross-over. Spindle apparatus begins to form, and nuclear envelope disappears. Physical exchange of chromosome pieces occur in Prophase I A tetrad 2 bivalents  Implications of physical exchange of chromosome pieces Crossing-over between maternal and paternal chromatids during meiosis I result in recombination of linked genes and provides more variation Crossing-over sites vary from one meiosis to another. Gene linkage - is the tendency of DNA sequences that are close together on a chromosome to be inherited together Meiosis I Metaphase I Chromosome pairs (bivalents) align across equatorial plane. Random assortment of maternal/paternal homologs occurs (different from metaphase of mitosis). Meiosis I Anaphase I Homologous chromosome pairs separate and migrate toward opposite poles. There is random assortment of chromosomes Meiosis I Telophase I Chromosomes complete migration, and new nuclear envelopes form, followed by cell division. Meiosis I reduces the chromosome number by half 2n = 6 n=3 + n=3  Cytokinesis I or Interkinesis is the cytoplasmic division after Meiosis I The two daughter cells are haploid cells but the chromosomes are still duplicated Can be a resting stage but NO further DNA replication takes place  Prophase II Chromosomes condense  Metaphase II Spindle forms and centromeres align on the equatorial plane.  Anaphase II Centromeres split and chromatids are pulled to opposite poles of the spindle (one sister chromatid from each pair goes to each pole).  Telophase II Chromatids complete migration, nuclear envelope forms, and cells divide, resulting in 4 haploid cells. Each progeny cell has one chromosome from each homologous pair, but these are not exact copies due to crossing-over  Some key points to remember Meiosis results in male and female gametes with halved chromosome number. Random assortment of chromosomes during meiosis results in gametes that may contain varied combinations of genes Synapsis and crossing-over cause chromatid exchange and result in recombination of linked genes  Comparison of mitosis and meiosis Mitosis One cell division Meiosi Two cell divisions s Two daughter cells Four daughter cells Chromosome number per nucleus Chromosome number halved in meiotic maintained products No synapsis and crossing-over Synapsis and crossing-over occur in Prophase I Sister chromatids separate at anaphase Sister chromatids do not separate in anaphase I but do at anaphase II Somatic cells Reproductive cells Conservative process Promote variation among the products of meiosis end