Biology – Premed Windsor University School of Medicine

and Health Sciences

DR. UCHE AMAEFUNA.

CHAPTER 20MITOSIS

There is more to lectures than the power point

slides!

Engage your mind

The Cell Cycle - Mitosis

Where it all began…You started as a cell smaller than

a period at the end of a sentence…

Going from an egg to a baby…. the original fertilized egg has to divide…

and divide…and divide…and divide…

Why do cells divide?• One-celled organisms

o For asexual reproduction (clones)

o a = without• Multi-celled organisms

o for growth & development from fertilized egg to adult

o for repair & replacement replace cells that die from normal wear & tear or from injury

amoeba

The Cell Cycle

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Dividing cells…• What has to be copied?

o DNAo organelleso cell membraneo lots of other molecules

enzymes

animal cell

plant cell

Copying DNA• A dividing cell duplicates its DNA

o creates 2 copies of all DNAo separates the 2 copies to opposite ends

of the cell o splits into 2 daughter cells

• But the DNA starts as a loosely wound in the nucleus

• If you tried to divide it like that, it could tangle & break

nucleus

cell

DNA

Organizing & packaging DNA

nucleus

cell

DNA

nucleus

cell

4 chromosomesin this organism

DNA in chromosomes in

everyday “working” cell

DNA in chromosomes in cell

getting ready to divide

DNA has been

“wound up”

Chromosomes of Human Female

46 chromosomes23 pairs

Chromosomes of Human Male

46 chromosomes23 pairs

double-strandedhuman chromosomesready for mitosis

DNA must be duplicated…

nucleus

cell

DNA in chromosomes

nucleus

cell

duplicated chromosomes

chromosomes in cell

4 single-stranded chromosomes

duplicatedchromosome

s

4 double-stranded chromosomes

Mitosis: Dividing DNA & cells• Stage 1: cell copies DNA

nucleus

cell

DNA

Copy DNA!

(interphase)

Mitosis: Dividing DNA & cells• Stage 2: DNA winds into chromosomes

o keeps it organized

nucleus

cell

duplicated chromosomes

like a Plateof spaghetti!

(prophase)

Mitosis: Dividing DNA & cells• Stage 3: Chromosomes line up

o chromosomes line up in middleo attached to protein “cables” called

Spindle Fibers that will help them move

duplicated chromosomeslined up in middle of cell

Meet in the Middle

(metaphase)

Mitosis: Dividing DNA & cells• Stage 4: Chromosomes separate

o chromosomes split, separating pairso start moving to opposite ends

chromosomes split & move to opposite ends

Pull APART

(anaphase)

Mitosis: Dividing DNA & cells• Stage 5: Cell starts to divide

o cells start to divideo nucleus forms again

Two Cells!

(telophase)

Mitosis: Dividing DNA & cells• Stage 6: DNA unwinds again

o cells separateo now they can do their every day jobs

(cytokinesis)

New “daughter” cells• Get 2 exact copies of original cells

Overview of mitosis

interphase prophase

metaphase anaphase telophase

cytokinesis

I.P.M.A.T.C.

Please Make Another Two Cells