Cell Division

Chapter 10

Why do you think cells in all plants and organisms need to divide? To replace damaged tissue To increase in size (the organism) To reproduce

Repair

• Cells are constantly repairing themselves• If a cell can’t be repaired new ones are

produced to fill the void

Growth

• Cells are also what create our size• As we grow our cells are constantly

reproducing • If the reproduction rate is faster than normal,

we grow

ReproductionAsexual

• Done by somatic or body cells

• Done also by unicellular organisms

• Creates identical daughter cells

Sexual

• Done by gametes or sex cells

• Creates genetically different daughter cells

What does the DNA look like inside the nucleus of the cell?

• When the cell is not dividing, the DNA looks like a tangled mass called CHROMATIN

When the cell is ready to divide, the DNA condenses into CHROMOSOMES

• Chromosome: a compacted piece of chromatin that is used for cell division

• Sister Chromatids: A pair of identical Chromosomes

• Centromere: The center section where the sister chromatids are connected

Sister chromatids

Centromere

TE

M 3

6,60

0

DNA supercoil

LE 8-4

Sister chromatids

Centromere

TE

M 3

6,60

0

Sister chromatids

Chromosomedistribution

todaughter

cells

Chromosomeduplication

How do cells divide?

• Cell Cycle: an orderly sequence of events where cells divide

• The cell cycle consists of two major phases– Interphase (90% of the time)– Mitotic Phase/cell division (10% of the time)

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html

The Cell Cycle

In humans and other mammals, cells that reproduce daily have a cell cycle that usually lasts 10 to 20 hours.

The Cell Cycle: series of events that cells go through from “birth” to reproduction

Interphase

• Phase where all metabolic processes and functions happen– Ex:

• Cellular respiration• Protein creation• Movement• Growth• Other desired function

Interphase

• Interphase is also when the cell prepares for cell division– Ex:

• Increases proteins• Duplicates organelles• Grows in size• Replication (duplication) of DNA

Mitotic Phase

• The division phase of the cell• There are two main parts of M phase

– Mitosis – Cytokinesis

Mitotic phase

• Mitosis– The division of a cells nucleus and DNA into two

equal parts– Creates two daughter nuclei

• Cytokinesis– The division of the cells cytoplasm

• Together they create two identical daughter cells

Mitosis

• Prophase:– Sister chromatids are formed– Formation of spindle– Nuclear envelope breaks down

• Metaphase:– Sister chromatids line up– Spindle is formed and attaching to chromosomes

LE 8-6a

INTERPHASE PROPHASE PROMETAPHASE

Kinetochore

Fragmentsof nuclearenvelope

CentrosomeEarly mitoticspindleChromatin

Centrosomes(with centriole pairs)

LM

250

Nucleolus Nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Centromere Spindle microtubules

Mitosis

• Anaphase:– Separation of sister chromatids– Spindle pulls chromosomes to either side of the cell

• Telophase:– Spindle breaks down– Nuclear envelopes form (2)– Chromosomes loosen to become chromatin

• Cytokinesis:– After mitosis, cell pulls apart to create two

identical cells

LE 8-6b

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Metaphaseplate

Spindle Daughterchromosomes

Nuclearenvelopeforming

Cleavagefurrow

Nucleolusforming

Cytokinesis in animal cells

Animal

• Formation begins with indentation

• Cell is pulled/ pinched until it breaks apart

Plants

• Formation begins with a disc containing cell wall materials

• A cell plate forms between the two nuclei

Cleavage furrow

Cleavagefurrow

Daughter cells

Cleavagefurrow

Contracting ring ofmicrofilaments

SE

M 1

40

Cytokinesis in plant cells• Formation begins with a disc containing cell wall materials• A cell plate forms between the two nuclei

Cell wall New cell wall

Daughter cellsCell plateVesicles containingcell wall material

Benign vs. malignant tumor• Benign tumor:

– abnormal mass of normal cells Malignant tumor:

• Masses of cells that result from the reproduction of cancer cells

• Cancer – Disease caused by cells that loose their ability to

control rate of division

Cell Differentiation