Cell Division Chapter 9

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 Sexual Done by somatic or body cells Done also by unicellular organisms Creates identical daughter cells 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? Sister chromatids Centromere TEM 36,600 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

DNA supercoil

Chromosome distribution to daughter cells LE 8-4 Sister chromatids Centromere TEM 36,600 Sister chromatids Chromosome distribution to daughter cells duplication

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 Cytokinesis 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: Metaphase: 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 LM 250  INTERPHASE PROPHASE PROMETAPHASE Early mitotic spindle Fragments of nuclear envelope Centrosomes (with centriole pairs) Centrosome Chromatin Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Centromere Spindle microtubules

Mitosis Anaphase: Telophase: Cytokinesis: 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 plate Cleavage furrow Nucleolus forming Nuclear ANAPHASE TELOPHASE AND CYTOKINESIS Metaphase plate Cleavage furrow Nucleolus forming Nuclear envelope forming Daughter chromosomes Spindle

Cytokinesis in animal cells Cleavage furrow Cleavage furrow Daughter cells Contracting ring of microfilaments SEM 140 Animal Plants Formation begins with indentation Cell is pulled/ pinched until it breaks apart Formation begins with a disc containing cell wall materials A cell plate forms between the two nuclei

Cytokinesis in plant cells Formation begins with a disc containing cell wall materials A cell plate forms between the two nuclei Cell wall New cell wall Daughter cells Cell plate Vesicles containing cell wall material

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.

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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 Indian 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.

2 diploid daughter cells 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

MITOSIS MEIOSIS TYPE OF CELL (that undergoes this division) (pages 195, 200, & 201) MITOSIS MEIOSIS 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

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 # of cells % Time/min. Interphase Prophase Metaphase Anaphase Telophase Total # of cells

Onion root tip