Cell DivisionCell Division

““All cells come from pre-existing cells.” All cells come from pre-existing cells.”

HOW?HOW?

PREVIEW VIDEO

MITOSISMITOSISMitosis – Mitosis – division of division of somatic cellssomatic cells..

In higher organisms, In higher organisms, mitosis only occurs in mitosis only occurs in somaticsomatic cells such as cells such as liverliver, , kidneykidney, and , and skinskin..

Mitosis does Mitosis does notnot occur in occur in sex cells sex cells ((spermsperm and and eggegg).). X

Mitosis

WHY MITOSIS?WHY MITOSIS?

1.1. Grow.Grow.

2.2. Repair and replace.Repair and replace.

WHAT ARE CHROMOSOMES?WHAT ARE CHROMOSOMES?

Chromosomes come in Chromosomes come in linked pairslinked pairs called called chromatidschromatids..

These are held together at a These are held together at a centromerecentromere..CHROMATIDS

CENTROMERE

What does mitosis look like?What does mitosis look like?

Video of mitosisVideo of mitosis

Understanding mitosis Understanding mitosis requires an understanding requires an understanding of the stages of mitosis.of the stages of mitosis.

What are the stages of mitosis?What are the stages of mitosis?

INTERPHASEINTERPHASE

A. Normal cell function.A. Normal cell function.

B. DNA is copied.B. DNA is copied.Plant and animal cells in interphase.

InterphaseInterphase

DNA Synthesis

Chromosome before DNA Synthesis

Chromosome after DNA Synthesis

ChromatidChromatid

Centromere

PROPHASEPROPHASE

A.A. Nuclear membrane dissolves.Nuclear membrane dissolves.

B.B. Chromosomes condense.Chromosomes condense.

CHROMATIN condenses into CHROMOSOMES

Easier to move when cells divide!

ProphaseProphase

C. C. SPINDLE FIBERSSPINDLE FIBERS attach to the attach to the CENTROMERECENTROMERE of each chromosome.of each chromosome.

ProphaseProphase

Plant and animal cells in prophase.

MetaphaseMetaphase

Chromosomes line up in middle of the cell.Chromosomes line up in middle of the cell.

Plant and animal cells in metaphase.

AnaphaseAnaphaseA.A. Spindle fibers pull chromatids apart.Spindle fibers pull chromatids apart.

B.B. Chromatids move to opposite ends.Chromatids move to opposite ends.

Plant and animal cells in Anaphase.

Telophase and CytokinesisTelophase and Cytokinesis

A.A. Chromosomes reach opposite ends.Chromosomes reach opposite ends.

B.B. Nuclear membrane is remade.Nuclear membrane is remade.

C.C. Cytokinesis – cell membrane pinches in Cytokinesis – cell membrane pinches in to form two new cells.to form two new cells.

In plants, cell wall forms between both cells. In plants, cell wall forms between both cells.

Telephase and CytokinesisTelephase and Cytokinesis

Plant and animal cells in Telophase.

CytokinesisCytokinesis

A good way of remembering the A good way of remembering the stages of mitosis is:stages of mitosis is:

II

PPreferrefer

MMangoesangoes

AAfterfter

TTeaea

OVERALL GOAL OF MITOSISOVERALL GOAL OF MITOSIS

Divide one cell into two cells.Divide one cell into two cells.

Keep the chromosome number the same.Keep the chromosome number the same.

Mitosis

ANIMATION OF PLANT CELL MITOSIS – click on “Plant Cell Mitosis” on left

MITOSIS IN NEWT LUNG CELLS – click on “Live Animal Mitosis” on left

MITOSIS VIDEO QUIZ

PLANT CELL

INTERPHASE

PLANT CELL

PROPHASE

PLANT CELL

METAPHASE

PLANT CELL

ANAPHASE

PLANT CELL

TELOPHASE

ANIMAL CELL

INTERPHASE

ANIMAL CELL

PROPHASE

ANIMAL CELL

METAPHASE

ANIMAL CELL

ANAPHASE

ANIMAL CELL

TELOPHASE

WHEN DOES MITOSIS OCCUR?WHEN DOES MITOSIS OCCUR?

G1 – normal cell functions

S – DNA is copied

G2 – normal cell functions

In otherwords: Cells do a lot more than just reproduce!

Cell Cycle Movie

HOW LONG DOES MITOSIS TAKE?HOW LONG DOES MITOSIS TAKE?

Bacteria –Bacteria –

Human Kidney cells – Human Kidney cells –

Human Nerve cells –Human Nerve cells –

Onion Root Tip - Onion Root Tip -

Every 20 minutes!

24 hours

Don’t divide after birth

720 minutes (12 hours)

HOW LONG DOES MITOSIS TAKE?HOW LONG DOES MITOSIS TAKE?

When does mitosis occur?

When during life does mitosis occur the fastest?

All through life!

Before birth.

# of cells in a phase# of cells in a phase

Total # of cellsTotal # of cells720 = Total time spent

in that phase *

Cancer – When Cell Cycle Doesn’t StopCancer – When Cell Cycle Doesn’t StopCell Cycle AnimationCell Cycle Animation

Cell Cycle doesn’t always keep goingCell Cycle doesn’t always keep going

Checkpoints to make sure cycle is done Checkpoints to make sure cycle is done correctly.correctly.

Checkpoint

Checkpoint Checkpoint

What happens during a checkpoint?What happens during a checkpoint?

Checkpoint #1Checkpoint #1 – During G1, Cdk checks if cell – During G1, Cdk checks if cell has grown enough.has grown enough.

Checkpoint #2 Checkpoint #2 – End of G2, p27 checks if – End of G2, p27 checks if chromosomes have been copied.chromosomes have been copied.

Checkpoint #3Checkpoint #3 – During metaphase, p53 – During metaphase, p53 checks if chromosomes are lined up in middle of checks if chromosomes are lined up in middle of cell. Mutated p53 is most frequent cause of cell. Mutated p53 is most frequent cause of cancer.cancer.

APOPTOSISAPOPTOSIS

If cell is too damaged, If cell is too damaged, apoptosisapoptosis or or “programmed cell death” occurs.“programmed cell death” occurs.

What organelle might be involved in this What organelle might be involved in this process?process?

LYSOSOME

APOPTOSISAPOPTOSIS

When else during life When else during life does “programmed does “programmed cell death” occur?cell death” occur?

Prior to birth

CANCERCANCER

If cell cycle isn’t performed correctly, cells If cell cycle isn’t performed correctly, cells become cancerous.become cancerous.

CANCER VIDEO