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Transcript
Cell Division Why do you think cells in all plants and organisms need to divide? To replace damaged tissue To increase in size To reproduce Repair • Cells are constantly repairing themselves • If a cell can’t be repaired new ones are produced to fill the void Growth • Cells are also what create our size • As we grow our cells are constantly reproducing • If the reproduction rate is faster than normal we grow Reproduction Asexual • Done by somatic or body cells • Done also by unicellular organisms • Creates identical daughter cells Sexual • Done by gametes or sex cells • Creates genetically different daughter cells What do we need for cell division? • Chromatin: a mass of DNA found in the nucleus What do we need for cell division? • Chromosome: a compacted piece of chromatin that is used for cell division • Sister Chromatids: A pair of identical Chromosomes • Centromere: The center section where the sister chromatids are connected Sister chromatids Centromere DNA supercoil LE 8-4 Sister chromatids Chromosome duplication TEM 36,600 Centromere Sister chromatids Chromosome distribution to daughter cells How do cells divide? • Cell Cycle: an orderly sequence of events where cells divide • The cell cycle consists of two major phases – Interphase (90% of the time) – Mitotic Phase (10% of the time) The Cell Cycle In humans and other mammals, cells that reproduce daily have a cell cycle that usually lasts 10 to 20 hours. The Cell Cycle: series of events that cells go through from “birth” to reproduction Interphase • Phase where all metabolic processes and functions happen – Ex: • • • • • Cellular respiration Protein creation Movement Growth Other desired function Interphase • Interphase is also when the cell prepares for cell division – Ex: • • • • Increases proteins Duplicates organelles Grows in size Duplication of DNA Mitotic Phase • The division phase of the cell • There are two main parts of M phase – Mitosis – Cytokinesis Mitotic phase • Mitosis – The division of a cells nucleus and DNA into two equal parts – Creates two daughter nuclei • Cytokinesis – The division of the cells cytoplasm • Together they create two identical daughter cells Mitosis • Prophase: – Sister chromatids are formed – Formation of spindle – Nuclear envelope breaks down • Metaphase: – Sister chromatids line up – Spindle is formed and attaching to chromosomes LE 8-6a INTERPHASE Centrosomes (with centriole pairs) Nucleolus Nuclear envelope PROPHASE Chromatin Plasma membrane Early mitotic spindle PROMETAPHASE Centrosome Chromosome, consisting of two sister chromatids Centromere Fragments of nuclear envelope Kinetochore Spindle microtubules Mitosis • Anaphase: – Separation of sister chromatids – Spindle pulls chromosomes to either side of the cell • Telophase: – Spindle breaks down – Nuclear envelopes form (2) – Chromosomes loosen to become chromatin • Cytokinesis: – Cell pulls apart to create two identical cells LE 8-6b METAPHASE ANAPHASE Cleavage furrow Metaphase plate Spindle TELOPHASE AND CYTOKINESIS Daughter chromosomes Nuclear envelope forming Nucleolus forming Cytokinesis in animal cells Animal • Formation begins with indentation • Cell is pulled/ pinched until it breaks apart Plants • Formation begins with a disc containing cell wall materials Cleavage • A cell furrowplate forms between the two nuclei Cleavage furrow Contracting ring of microfilaments Daughter cells Cytokinesis in plant cells • Formation begins with a disc containing cell wall materials • A cell plate forms between the two nuclei Cell wall Vesicles containing cell wall material New cell wall Cell plate Daughter cells Benign vs. malignant tumor • Benign tumor: – abnormal mass of normal cells Malignant tumor: • Masses of cells that result from the reproduction of cancer cells • Cancer – Disease caused by cells that loose their ability to control rate of division Meiosis • Organisms that reproduce sexually have specialized cells called gametes (sex cells) • Gametes are the result of a type of cell division called meiosis Diploid and haploid • Almost all human cells are diploid or containing two homologous sets of chromosomes 2n = 46 • Eggs and sperm cells (gametes) are haploid or containing a single set of chromosomes n = 23 HUMAN KARYOTYPE A display of all the 46 chromosomes of an Individual. 9.5 page 2 ORGANISM (Genus species) NUMBER OF CHROMOSOMES Homo sapiens (human)______________________________46 Mus musculus (house mouse)_________________________40 Drosophila melanogaster (fruit fly)_____________________8 Caenorhabditis elegans (microscopic roundworm)_________12 Saccharomyces cerevisiae (budding yeast) ______________32 Arabidopsis thaliana (plant in the mustard family) ________10 Xenopus laevis (South African clawed frog)______________36 Canis familiaris (domestic dog)________________________78 Gallus gallus (chicken) ______________________________28 Zea mays (corn or maize)____________________________20 Muntiacus reevesi (the Chinese muntjac, a deer) _________23 Muntiacus muntjac (its native american cousin) __________6 Myrmecia pilosula (an ant) ___________________________2 Parascaris equorum var. univalens (parasitic roundworm)___2 Cambarus clarkii (a crayfish)__________________________200 Equisetum arvense (field horsetail, a plant)______________216 Horsetail MITOSIS Meiosis haploid egg and sperm diploid zygote In the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis produces an embryo with numerous cells that continue to multiply and develop. http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison%20of%20Meiosis%20and%20Mitosis MEIOSIS MITOSIS Original diploid cell 2n 2n 2n 2 diploid daughter cells Genetic variation is a result of two processes that occurs during meiosis: • Independent assortment of chromosomes, and • Crossing over • During metaphase I, the independent assortment of chromosomes that end up in the resulting cells occurs randomly • Crossing over: exchange of genetic material between homologous chromosomes during prophase I of meiosis • Genetic recombination: new combination of genetic information in a gamete as a result of crossing over during prophase I of meiosis (pages 195, 200, & 201) TYPE OF CELL (that undergoes this division) # OF CELL DIVISIONS Starts/ends as diploid or haploid cell # OF DAUGHTER CELLS # OF CHROMOSOMES AFTER DIVISION EXCHANGE OF DNA (Y/N) UNIQUE OR IDENTICAL CELL AFTER DIVISION MITOSIS MEIOSIS Development of egg and sperm Onion Root Cell Observations • Using the largest magnification (X400), find a section of the onion root (towards the tip works better). • Count only the cells in one of the quadrants. • Try to find the different stages of cell division, and fill out the table bellow as accurately as you can. Phase Interphase Prophase Metaphase Anaphase Telophase Total # of cells # of cells % Time/min. Onion root tip