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 gametes or sex cells Creates genetically different daughter cells • Done by somatic or body cells • Done also by unicellular organisms • Creates identical daughter cells
What do we need for cell division? • Chromatin: a mass of DNA found in the nucleus
Sister chromatids 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 Centromere TEM 36,600
LE 8-4 Sister chromatids Chromosome duplication Sister chromatids Centromere Chromosome distribution to daughter cells TEM 36,600
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 LM 250 INTERPHASE PROPHASE PROMETAPHASE Fragments of nuclear envelope Early mitotic spindle Centrosome Centrosomes (with centriole pairs) Kinetochore Chromatin Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Centromere 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 TELOPHASEAND CYTOKINESIS Cleavage furrow Nucleolus forming Metaphase plate Nuclear envelope forming Daughter chromosomes Spindle
Cytokinesis in animal cells Animal Plants Formation begins with a disc containing cell wall materials A cell plate forms between the two nuclei • Formation begins with indentation • Cell is pulled/ pinched until it breaks apart Cleavage furrow Cleavage furrow SEM 140 Cleavage furrow Contracting ring of microfilaments Daughter cells
Cytokinesis in plant cells Cell wall New cell wall • Formation begins with a disc containing cell wall materials • A cell plate forms between the two nuclei Vesicles containing cell wall material 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.
ORGANISM (Genus species) NUMBER OF CHROMOSOMES
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%20Mitosishttp://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
Crossingover: 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
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.