Growing and Repairing ourselves through cell division - Mitosis

Cell Division—Mitosis Notes

Cell Division — process by which a cell divides into 2 new cells

• Why do cells need to divide?

1.Living things grow by producing more cells, NOT because each cell increases in size

2.Repair of damaged tissue

3.If cell gets too big, it cannotget enough nutrients into the cell and wastes out of the cell

Skin cancer - the abnormal growth of

skin cells - most often develops on skin

exposed to the sun.

Cell reproduce constantly.

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Keeping Cells Identical

The instructions for making cell parts are in the DNA

Each cell must have it’s own DNA

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DNA ReplicationSo cells need to make a copy of the DNA before dividing

When one of our cells splits in two new ones each new cell will then it’s own copy of the DNA

Original DNA

strand

Two new,

identical DNA

strands

DNA• DNA is located in the nucleus and controls all cell activities including cell division

• When the cell does not need to divide and make more cells , DNA is found in a Long and thread-like form called chromatin

• When the cell is getting ready to divide the DNA is found in a Doubled, coiled, short DNA in a dividing cell is called chromosome

Chromatin

Duplicates itself

Coils up into chromosomes

•Chromatin to chromosomes illustration:

Why does DNA need to change from chromatin to chromosome?

Easier to divide

• The original cell is called the parent cell; the two newcells it divides into are called daughter cells

• Before cell divides, the cell makes copies all of its DNA, so each daughter cell gets a complete set of informationfrom parent cell

• Each daughter cell is exactly like the parent cell – samekind and number of chromosomes as the original cell

Parent Cell

2 Daughter

Cells

Chromosome number• Every organism has its own specific number of

chromosomesExamples: Human = 46 chromosomes or 23 pairs

Dog = 78 chromosomes or 39 pairsGoldfish = 94 chromosomes or 47 pairsLettuce = 18 chromosomes or 9 pairs

• All body cells in an organism have the same kind and number of chromosomes

Examples: Human = 46 chromosomesHuman skin cell = 46 chromosomes Human heart cell = 46 chromosomesHuman muscle cell = 46 chromosomes

Fruit fly = 8 chromosomesFruit fly skin cell = 8 chromosomesFruit fly heart cell = 8 chromosomesFruit fly muscle cell = 8 chromosomes

Cell Cycle

Some things must happen before cells can growand divide

Interphase

• This is the time where the cell grows (makes all it needs to do it’s job right)

• continues normal cell activities

• Makes a copy of it’s DNA as it is getting ready to divide

• Makes a copy of the organelles inside

• So it makes sure it has 2 of everything and is ready to divide

•The cell spends most of its life (90%) cycle in Interphase

Mitosis – is what the division of cell is called

Each new cell will get it’s own nucleus, the same number of chromosomes with mitosis

•Mitosis occurs in all the body cells

Why does mitosis occur?

So each new daughter cell has nucleus with a complete set of chromosomes

Interphase

Cell

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

Anaphase—(Apart)

Prophase Metaphase—(Middle)

Telophase—(Two)Anaphase—(Apart)

• There are 4 phases in mitosis

Chromosomes go from spaghetti looking DNA to a tight regular shape (coil up)

Nuclear membrane disappears

Spindle fibers form ( fibers that will help move the chromosomes around)

Prophase

Chromosomes line up in middle of cell

Spindle fibers connectto chromosomes

Metaphase—(Middle)

Chromosome copies divide

Spindle fibers pull chromosomes to opposite poles

Anaphase—(Apart)

Chromosomes uncoil back to spaghetti like shape (they stay like this in chromatin when not dividing)

Nuclear membranes form

2 new nuclei are formed (one for each cell )

Spindle fibers disappear And the outer membrane of the

cell pinches ready to close

Telophase—(Two)

Cytokinesis — the membrane closes off after each new cell has the chromosomes , it’s own nucleus ,cytoplasm and organelles

•After mitosis and cytokinesis, the cell returns to Interphaseto continue to grow and continue it’s own cell activities and jobs until it is time to divide again

Summary: Cell Cycle

Interphase Mitosis Cytokinesis

•When cells become old or damaged, they die and are replaced with new cells

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

Cell Division Control

•DNA controls all cell activities including cell division

•Some cells lose their ability to control their rate of cell division – the DNA of these cells has become damaged or changed (mutated)

•These super-dividing cells form masses called tumors

•Benign tumors are not cancer – these cells do not spread to other parts of the body

•Malignant tumors are cancer – these cells break loose and can invade and destroy healthy tissuein other parts of the body

•Cancer is not just one disease, but many diseases – over 100different types of cancers

Please: Pairs of chromosomes aPPear

in Prophase

•Make: chromomes Meet in Middle

during Metaphase

•A: chromomes are pulled Apart

during Anaphase

•T: Two cells with their own nucleus appear in Telophase

The menmonic "Please Make A Twin" makes it easier to

remember the active phases of cell division.

Prophase: Metaphase:

Anaphase: Telophase: