1 1 Asexual Reproduction The Cell Cycle. 2 DNA must be copied or replicated before cell division DNA...

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Asexual Reproduction

The Cell Cycle

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DNA must be DNA must be copied or copied or replicatedreplicated before cell before cell division division

Each new cell Each new cell will then have will then have anan identical identical copy copy of the of the DNADNA

Original DNA Original DNA strandstrand

Two new, Two new, identical DNA identical DNA strandsstrands

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Parent CellParent Cell

Two Two identical identical daughter daughter cellscells

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The DNA of The DNA of prokaryotes prokaryotes (bacteria) is (bacteria) is

one, circular one, circular chromosome chromosome attached to the attached to the inside of the inside of the cell membranecell membrane

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AllAll eukaryoticeukaryotic cells store cells store genetic information in genetic information in chromosomeschromosomes

Most eukaryotes have between Most eukaryotes have between 10 10 and 50 chromosomesand 50 chromosomes in their body in their body cellscells

Human body cells Human body cells havehave 4646 chromosomes or 23 identical pairschromosomes or 23 identical pairs

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Each chromosome is composed Each chromosome is composed of a of a single, tightly coiled DNA single, tightly coiled DNA moleculemolecule

ChromosomesChromosomes can’t be seen can’t be seen when cellswhen cells aren’t dividingaren’t dividing and and are called are called chromatinchromatin

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Duplicated chromosomes are called chromatids & are held together by the centromere

Called Sister ChromatidsCalled Sister Chromatids

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AA picturepicture of the of the chromosomes chromosomes from a human cell from a human cell arranged in pairs arranged in pairs by sizeby size

First 22 pairs are First 22 pairs are called called autosomesautosomes

Last pair are the Last pair are the sex chromosomessex chromosomes

XXXX female or female or XY XY malemale

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Y - ChromosomeY - Chromosome

X - ChromosomeX - Chromosome

The Y Chromosome DecidesThe Y Chromosome Decides

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Prokaryotes such Prokaryotes such as as bacteriabacteria divide divide into 2 identical into 2 identical cells by the process cells by the process of of binary fissionbinary fission

Single chromosome Single chromosome makes a copy of makes a copy of itselfitself

Cell wall forms Cell wall forms between the between the chromosomes chromosomes dividing the celldividing the cell

Parent cellParent cell

2 identical daughter cells2 identical daughter cells

Chromosome Chromosome relicatesrelicates

Cell splitsCell splits

How do little elephants grow up to be BIG elephants?

The process of asexual reproduction in

eukaryotes begins after a sperm fertilizes

an egg.

Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun.

Cancer develops when cells that reproduce by asexual reproduction divide out of control.

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Daughter Daughter CellsCells

DNA CopiedDNA Copied

Cells Cells MatureMature

Cells prepare Cells prepare

for Divisionfor Division

Nuclear DivisionNuclear Division

Cell Divides into 2 Identical cellsCell Divides into 2 Identical cells

Cytoplasmic Division

Animated Cell Cyclehttp://www.cellsalive.com/mitosis.htm

• Interphase

• Prophase

• Metaphase

• Anaphase

• Telophase & Cytokinesis

• Chromosomes are copied (# doubles)• Chromosomes appear as threadlike coils

(chromatin) at the start, but each chromosome and its copy(sister chromosomes) change to sister chromatids at end of this phase

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11stst growth stage growth stage after cell divisionafter cell division CellsCells maturemature by making more by making more

cytoplasm & organellescytoplasm & organelles Cell carries on its Cell carries on its normal normal

metabolic activitiesmetabolic activities CellsCells can leave can leave this phase (Gthis phase (G00)and )and

go through a go through a rest phaserest phase and then and then reenterreenter before proceeding to the before proceeding to the S phaseS phase

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SynthesisSynthesis PhasePhase DNADNA is copied or is copied or replicatedreplicated

Two Two identical identical copies of copies of DNADNA

Original DNAOriginal DNA

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22ndnd Growth Growth StageStage OccursOccurs after DNA has been after DNA has been

copiedcopied All cell All cell structures needed for structures needed for

division division are made (e.g. are made (e.g. centrioles)centrioles)

BothBoth organelles & proteins organelles & proteins are are synthesizedsynthesized

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What the cell looks likeWhat the cell looks like

Animal Cell

What’s occurring

Animal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

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Division of Division of the the nucleusnucleus

Only occurs in Only occurs in eukaryoteseukaryotes

HasHas fourfour stagesstages

Doesn’t occur Doesn’t occur in some cells in some cells such assuch as brain brain cellscells

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ProProphasephaseMetaMetaphasephaseAnaAnaphasephaseTeloTelophasephase

• Mitosis begins (cell begins to divide)• Centrioles (or poles) appear and begin to move to

opposite end of the cell (animal cells only). • Spindle fibers form between the poles.• Nucleus and nucleolus disappear• Chromatin condenses (coils) to form chromosomes



Spindle fibers

Centrioles

• Chromatids (or pairs of chromosomes) attach to the spindle fibers.

• Chromosomes are now lined up at Chromosomes are now lined up at the equatorthe equator

• Occurs rapidly• Chromatids (or pairs of chromosomes)

separate and begin to move to opposite ends of the cell.

• Two new nuclei and nucleoli form. • Chromosomes appear as chromatin (threads rather

than rods).• Cleavage furrow begins to forms in animal cells

and a cell plate begins to form in plant cells• Mitosis ends.

• Cell membrane moves inward to divide the cytoplasm and create two daughter cells – each with its own nucleus with identical chromosomes.

Animal Mitosis -- Review

Interphase

Prophase

Metaphase

Anaphase

Telophase

Interphase

Plant Mitosis -- ReviewInterphase

Prophase

Metaphase

Anaphase

Telophase

Interphase

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- Cell Division

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http://www.cellsalive.com/mitosis.htm

1 1 Asexual Reproduction The Cell Cycle. 2 DNA must be copied or replicated before cell division DNA...

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