Cell Division Chapter 9. Why do you think cells in all plants and organisms need to divide? To...
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Transcript of Cell Division Chapter 9. Why do you think cells in all plants and organisms need to divide? To...
![Page 1: 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.](https://reader030.fdocuments.net/reader030/viewer/2022032705/56649dd05503460f94ac5916/html5/thumbnails/1.jpg)
Cell Division
Chapter 9
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Why do you think cells in all plants and organisms need to divide?
To replace damaged tissue To increase in size To reproduce
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Repair
• Cells are constantly repairing themselves• If a cell can’t be repaired new ones are
produced to fill the void
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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
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ReproductionAsexual
• 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
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What do we need for cell division?
• Chromatin: a mass of DNA found in the nucleus
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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
TE
M 3
6,60
0
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DNA supercoil
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LE 8-4
Sister chromatids
Centromere
TE
M 3
6,60
0
Sister chromatids
Chromosomedistribution
todaughter
cells
Chromosomeduplication
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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)
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The Cell Cycle
In humans and other mammals, cells that reproduce daily have a cell cycle that usually lasts 10 to 20 hours.
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The Cell Cycle: series of events that cells go through from “birth” to reproduction
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Interphase
• Phase where all metabolic processes and functions happen– Ex:
• Cellular respiration• Protein creation• Movement• Growth• Other desired function
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Interphase
• Interphase is also when the cell prepares for cell division– Ex:
• Increases proteins• Duplicates organelles• Grows in size• Duplication of DNA
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Mitotic Phase
• The division phase of the cell• There are two main parts of M phase
– Mitosis – Cytokinesis
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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
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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
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LE 8-6a
INTERPHASE PROPHASE PROMETAPHASE
Kinetochore
Fragmentsof nuclearenvelope
CentrosomeEarly mitoticspindleChromatin
Centrosomes(with centriole pairs)
LM
250
Nucleolus Nuclearenvelope
Plasmamembrane
Chromosome, consistingof two sister chromatids
Centromere Spindle microtubules
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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
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LE 8-6b
METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS
Metaphaseplate
Spindle Daughterchromosomes
Nuclearenvelopeforming
Cleavagefurrow
Nucleolusforming
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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
• A cell plate forms between the two nuclei
Cleavage furrow
Cleavagefurrow
Daughter cells
Cleavagefurrow
Contracting ring ofmicrofilaments
SE
M 1
40
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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 cellsCell plateVesicles containingcell wall material
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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
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Meiosis
• Organisms that reproduce sexually have specialized cells called gametes (sex cells)
• Gametes are the result of a type of cell division called meiosis
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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
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HUMAN KARYOTYPE
A display of all the 46chromosomes of an Individual.
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9.5 page 2
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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
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Horsetail
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MITOSIS
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Meiosis
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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.
haploid egg and sperm
diploid zygote
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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
2n
2n 2n
MITOSISMEIOSIS
Original diploid cell
2 diploid daughter cells
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Genetic variation is a result of two processes that occurs during meiosis:
• Independent assortment of chromosomes, and • Crossing over
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• During metaphase I, the independent assortment of chromosomes that end up in the resulting cells occurs randomly
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• Crossing over: exchange of genetic material between homologous chromosomes during prophase I of meiosis
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• Genetic recombination: new combination of genetic information in a gamete as a result of crossing over during prophase I of meiosis
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(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
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Development of egg and sperm
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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
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Onion root tip
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