copyright pearson prentice hall 1.6 cell division
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1.6 Cell Division
Essential Idea
• Cell division is essential but must be controlled.
• In unicellular organisms, division of one cell reproduces a new organism
• Multicellular organisms depend on cell division for:
•Cell size is limited
•Development from a fertilized cell
•Growth
•Repair
LE 12-2
Reproduction
100 µm
Tissue renewalGrowth and development
20 µm200 µm
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Limits to Cell Growth
Limits to Cell Growth
The larger a cell becomes, the more demands the cell places on its DNA.
In addition, a large cell will have trouble moving enough nutrients and wastes across its cell membrane.
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IB Assessment Statement
• Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis
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LE 12-5
G1
G2
S(DNA synthesis)
INTERPHASE
Cytokin
esis
MITOTIC(M) PHASE
Mito
sis
Phases of the Cell Cycle
• The cell cycle consists of
Mitotic (M) phase (mitosis and cytokinesis)
Interphase (cell growth and copying of chromosomes in preparation for cell division)
• Interphase (about 90% of the cell cycle) can be divided into subphases:
G1 phase (“first gap”)S phase (“synthesis”)G2 phase (“second gap”)
LE 12-5
G1
G2
S(DNA synthesis)
INTERPHASE
Cytokin
esis
MITOTIC(M) PHASE
Mito
sis
Interphase (about 90% of the cell cycle) can be divided into subphases:
G1 phase (“first gap”)First phase of growthNew organelles formedBiochemical activity
S phase (“synthesis”) chromosomes are copied (DNA replication) Two identical structures are formed called ChromatidsChromatids until mitosis
G2 phase (“second gap”)More growth of cellPreparation for Mitosis
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ChromosomesS- Phase of Interphase
– Chromosomes are copied
– Genetic information (DNA) is passed from one generation to the next on chromosomes.
– This process, it is called DNA replication
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ChromosomesEach chromosome consists of two identical “sister” chromatids.
Each pair of chromatids is attached at an area called the centromere.
When the cell divides, the chromatids separate.
Each new cell gets one chromatid.
Sister chromatids
Centromere
• Mitosis is conventionally divided into four phases:
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis is well underway by late telophase
Cell Cycle Animation: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html
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Cell Cycle
Events of the Cell Cycle
LE 12-6ca
G2 OF INTERPHASE PROPHASE PROMETAPHASE
LE 12-6da
METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS
10
µm
IB Assessment Statement
• Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).
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Mitosis
Mitosis
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Section 10-2ProphaseSpindle
forming
Chromosomes (paired
chromatids)Centromere
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Mitosis
Prophase
Mitosis Animation:
•http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html
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Mitosis
Prophase
Prophase is the first and longest phase of mitosis.
The MTOC/ centrosomes separate and take up positions on opposite sides of the nucleus.
MTOC – Microtubules organizing center
Spindle forming
CentromereChromosomes(paired chromatids)
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Mitosis
Chromatin condenses into chromosomes.
The centrioles separate and a spindle begins to form.
The nuclear envelope breaks down.
Spindle forming
CentromereChromosomes(paired chromatids)
Chromatin condenses into chromosomes.
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MTOC
• MTOC/ controsomes form the mitotic spindle also called spindle microtubules.
• The mitotic spindle (spindle microtubules) is an structure that controls chromosome movement during mitosis
• The MTOC/ centrosomes replicates, forming two MTOC/ centrosomes that move to opposite ends of the cell, as mitotic spindle grows out from them
LE 12-7
SpindleMicrotubules
Chromosomes
Sisterchromatids
MTOC/ Centrosome
Metaphaseplate
spindlemicrotubules
0.5 µm1 µmMTOC
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MTOC
MTOC
Spindle
Mitosis
Click to Continue
Metaphase
Metaphase
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Mitosis
Metaphase
The second phase of mitosis is metaphase.
The chromosomes line up across the center of the cell.
Microtubules connect the centromere of each chromosome to the poles of the spindle.
MTOC
Spindle
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Individual chromosomes
Anaphase
Mitosis
Anaphase
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Mitosis
Anaphase
Anaphase is the third phase of mitosis.
The sister chromatids separate into individual chromosomes.
The chromosomes continue to move until they have separated into two groups.
Individualchromosomes
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Nuclear envelope reforming
Telophase
Mitosis
Telophase
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Mitosis
Telophase
Telophase is the fourth and final phase of mitosis.
Chromosomes gather at opposite ends of the cell and lose their distinct shape.
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Mitosis
A new nuclear envelope forms around each cluster of chromosomes.
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Cytokinesis
Cytokinesis
Cytokinesis
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Cytokinesis
During cytokinesis, the cytoplasm pinches in half.
Each daughter cell has an identical set of duplicate chromosomes
• More animations/ tutorials of mitosis:
• http://www.johnkyrk.com/mitosis.html
• http://bcs.whfreeman.com/thelifewire/content/chp09/0902001.html
• https://www.youtube.com/watch?v=L0k-enzoeOM&feature=player_embedded
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Cytokinesis: A Closer Look
• In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow
Animation: Cytokinesis
LE 12-9a
Cleavage furrow100 µm
Contractile ring ofmicrofilaments
Daughter cells
Cleavage of an animal cell (SEM)
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Cytokinesis in Plants
In plants, a structure known as the cell plate forms midway between the divided nuclei.
Cell wallCell plate
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Cytokinesis in Plants
The cell plate gradually develops into a separating membrane.
A cell wall then begins to appear in the cell plate.
LE 12-9b
1 µm
Daughter cells
Cell plate formation in a plant cell (TEM)
New cell wallCell plate
Wall ofparent cell
Vesiclesformingcell plate
LE 12-10
NucleusCell plateChromosomesNucleolus
Chromatincondensing 10 µm
Prophase. The chromatin is condensing.The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is starting to form.
Prometaphase. Wenow see discrete chromosomes; each consists of two identical sister chromatids. Laterin prometaphase, the nuclear envelope will fragment.
Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate.
Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro- tubules shorten.
Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.
Cell Cycle Summary
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IB ASSESSMENT STATEMENT
• Explain how mitosis produces two genetically identical nuclei.
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IB Assessment Statement
• State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or Tissue
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What is Cancer?
• Tumours are not foreign invaders. They arise from the same material used by the body to construct its own tissues. Tumours use the same components -human cells- to form the jumbled masses that disrupt biological order and function and, if left unchecked, to bring the whole complex, life sustaining edifice that is the human body crashing down'.–R. Weinberg, R. (1998) One Renegade Cell. London:Phoenix, Science Masters Series.
• 'Cancer is, in essence a genetic disease'–Volgestein and Kinzler
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Uncontrolled Cell Growth
• Uncontrolled Cell Growth
–Cancer is a disorder in which some of the body's own cells lose the ability to control growth.
–How are cancer cells different from other cells?
Uncontrolled Cell Growth
–Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.
–Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.
Understandings
• Cyclins are involved in the control of the cell cycle.
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Understandings
• Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.
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IB Assessment Statement
• State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis
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State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis
• Growth: multicellular organisms increase their size through growth. This growth involves increasing the number of cells through mitosis. These cells will differentiate and specialise their function.
• Embryonic development is when the fertilised egg cell (zygote) divides to form the multicellular organism. Each cell in the organisms is identical (genetically) to all the other cells. However, each cell will express only a few of its genes to determine its overall specialisms, a process called differentiation. In this way a stem cell may becomes a muscle, or it may become a nerve cell or any one of the many different kinds of cells found in a complex multicellular organism. The best book about this process for the interested reader is
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State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis
• Tissue Repair: As tissues are damaged they can recover through replacing damaged or dead cells. This is easily observed in a skin wound. More complex organ regeneration can occur in some species of amphibian.
• Asexual Reproduction: This the production of offspring from a single parent using mitosis. The offspring are therefore genetically identical to each other and to their “parent”- in other words they are clones. Asexual reproduction is very common in nature, and in addition we humans have developed some new, artificial methods. Bacteria DO NOT asexually reproduce by mitosis but rather by a process called Binary Fission.
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