Bellringer

• How are chromotin and chromosomes different ?

• Explain what Binary Fission is?

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Agenda

• NOTES: Cell Division– Purpose of Division– Chromatin & Chromosomes– Binary Fission (bacteria division)– Cell Cycle (eukaryotic division)– Introduction to Steps of Mitosis

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Why do cells divide?• Unicellular creatures divide

as a way to reproduce. Their “children” are just separated halves of the “parent”.

• Multicellular lifeforms divide their cells in order to grow larger and to replace dead cells. Your body replaces about 300,000 cells each minute.

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Parent and Daughter Cells• Cell division creates 2 identical copies

– The cell that is divided is called the “Parent Cell”

– The 2 new cells are called “Daughter Cells”

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Parent CellParent Cell

Two Two identical identical daughter daughter

cellscells

Daughter Cell DNA• Remember that DNA carries all of the

instructions for a cell.

• Every daughter cell needs a complete set of its parent’s DNA. Without a full set information would be lost.

• This means that a parent cell must create two sets of DNA before dividing so each daughter can have one.

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Chromatin & Chromosomes• DNA is usually packed loosely within the

cell. DNA in this “normal” state is called chromatin.

• Before dividing, a cell’s DNA will form large, tightly packed clumps called chromosomes. This is done to allow pieces of DNA to be easily sorted and moved around.

• After dividing, a chromosome will loosen up and the DNA converts back into chromatin.

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ChromosomChromosomeses

CHROMATIN ~~~~~ CHROMOSOMES

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Cell Division in Cell Division in ProkaryotesProkaryotes

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Prokaryotic ChromosomeProkaryotic Chromosome

• Remember that Remember that prokaryotes have no prokaryotes have no nucleus to contain nucleus to contain DNADNA

• Their DNA forms one, Their DNA forms one, circular chromosome circular chromosome attached to the inside attached to the inside of the cell membraneof the cell membrane

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Cell Division in Cell Division in ProkaryotesProkaryotes

Prokaryotes such as Prokaryotes such as bacteria divide by a quick bacteria divide by a quick and simple process called and simple process called binary fissionbinary fission

First the single First the single chromosome makes a copy chromosome makes a copy of itselfof itself

A cell wall then forms A cell wall then forms between the chromosomes between the chromosomes dividing the celldividing the cell

Prokaryotic Division Video

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Eukaryotic Division: Cell Cycle

• Eukaryotic cells divide by a longer and more complex method known as the cell cycle.

• There are 4 stages of the cell cycle. – G1: First Growth

– S: Synthesis Stage

– G2: Second Growth

– M: Mitosis

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GG11 Stage Stage• GG11 is the first growth stage of a is the first growth stage of a

newly created cell.newly created cell.

• The cell matures by growing larger The cell matures by growing larger and creating more organelles.and creating more organelles.

• Cell carries on its normal Cell carries on its normal metabolic activitiesmetabolic activities

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S StageS Stage• S is the synthesis stage. The cell copies S is the synthesis stage. The cell copies

all of its DNA to make a second set. all of its DNA to make a second set. • This prepares for division at later stagesThis prepares for division at later stages

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GG22 Stage Stage• This second growth stage This second growth stage

occurs after DNA has been occurs after DNA has been copiedcopied

• The cell begins creating The cell begins creating specialized organelles and specialized organelles and structures that will do the work structures that will do the work of dividing.of dividing.

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Cell CycleCell Cycle

DaughteDaughter Cellsr Cells

DNA DNA CopiedCopied

Cells Cells MaturMatur

ee

Cell prepares Cell prepares for Divisionfor Division

Cell Divides into Cell Divides into Identical cellsIdentical cells

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M stageM stage• Mitosis is the division process.Mitosis is the division process.

• During this time DNA clumps During this time DNA clumps into chromosomes and then is into chromosomes and then is separated into two groups.separated into two groups.

• When the cell divides, each When the cell divides, each daughter receives half of the daughter receives half of the chromosomes. chromosomes.

5 Stages of Mitosis• Mitosis is divided into 5 steps that we

will study in detail in future lessons.– Prophase– Metaphase– Anaphase– Telophase– Cytokinesis

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Cell Cycle Summary Video

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