copyright pearson prentice hall 1.6 cell division

Copyright Pearson Prentice Hall

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


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.

IB Assessment Statement

• Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis


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


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


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

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html





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


• Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).



Mitosis

Mitosis


Section 10-2ProphaseSpindle

forming

Chromosomes (paired

chromatids)Centromere

Click to Continue

Mitosis

Prophase

Mitosis Animation:

•http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html


http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html






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)


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.


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


MTOC

MTOC

Spindle

Mitosis

Click to Continue

Metaphase

Metaphase


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


Individual chromosomes

Anaphase

Mitosis

Anaphase


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


Nuclear envelope reforming

Telophase

Mitosis

Telophase


Mitosis

Telophase

Telophase is the fourth and final phase of mitosis.

Chromosomes gather at opposite ends of the cell and lose their distinct shape.


Mitosis

A new nuclear envelope forms around each cluster of chromosomes.


Cytokinesis

Cytokinesis

Cytokinesis


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


http://www.johnkyrk.com/mitosis.html

http://bcs.whfreeman.com/thelifewire/content/chp09/0902001.html

http://bcs.whfreeman.com/thelifewire/content/chp09/0902001.html

https://www.youtube.com/watch?v=L0k-enzoeOM&feature=player_embedded

https://www.youtube.com/watch?v=L0k-enzoeOM&feature=player_embedded

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)


Cytokinesis in Plants

In plants, a structure known as the cell plate forms midway between the divided nuclei.

Cell wallCell plate


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 microtubules 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


IB ASSESSMENT STATEMENT

• Explain how mitosis produces two genetically identical nuclei.



• State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or Tissue


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


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.


Understandings

• Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.



• State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis


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


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.


copyright pearson prentice hall 1.6 cell division

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