DNA and Cell Division

Mitosis in Animals

Background Information

Once an egg becomes fertilized, cellular divisions begins, eventuallyproducing a whole organism

An Integrated

Organism

All cells derived from the zygote contain the same genetic material

Organization of DNA

• All cells have DNA (chromosomes).

• Almost all cells divide for reproduction, growth or repair.

• Each new cell needs the exact same DNA as the original cell.

• The original cell is called the mother cell and the two new cells are called daughter cells.

• The DNA in the nucleus must replicate before the cell divides.

Common Name Genus and SpeciesDiploid ChromosomeNumber

Buffalo Bison bison 60

Cat Felis catus 38

Cattle Bos taurus, B. indicus 60

Dog Canis familiaris 78

Donkey E. asinus 62

Goat Capra hircus 60

Horse Equus caballus 64

Human Homo sapiens 46

Pig Sus scrofa 38

Sheep Ovis aries 54

Chromosome Number in Different Species

Number of genes in sequenced genomes

• E. coli 4300• Yeast 6000• Roundworm 18,600• Fruit fly 13-14,000• Mosquito 13-14,000• Mouse 30-35,000• Human 30-35,000

A non-dividing cell:

• 90% of a cell’s life is spent growing, not dividing

• This phase is called interphase• The DNA in this phase is not condensed;

thus is chromatin• At some point during this phase the DNA

is doubled or replicated• Two copies are made, one for each of the

new cells

• Once replication occurs, the chromatin folds up to form chromosomes

• This only occurs when the cell is about to divide• The duplicated chromosomes attach to each

other at the centromere• Each individual copy of one chromosome is

known as a chromatid• When chromatids are joined at the centromere,

they are known as a single chromosome.

A piece of DNA or chromosome in an undividing cell

Same piece now has replicated and super coiled ready for cell division.

sister chromatids

centromere

Also during interphase…

• Additional organelles are produced

• Cell membrane enlarged to allow cell growth

• When the cell becomes too big to function it must divide

– What would the SA/V ratio of this cell be…large or small?

Interphase

• The cell grows

• New organelles are formed

• Duplicate chromosomes are produced

• The chromosomes are uncoiled and invisible

• This uncoiled chromosomes are known as a chromatin

Cell division/reproduction

• Interphase is not considered to be part of cell reproduction.

• It is simply the growth of the cell and the duplication of the chromosomes.

• Cell reproduction consists of two separate stages known as mitosis and cytokinesis.

• Cell division = mitosis + cytokinesis• A parent cell will produce 2 daughter cells.

In cell division each chromosome is replicated and then the cell (and nucleus) divides

Cell Reproduction• Original cell divides into two

genetically identical daughter cells• Complete set of genetic information

passed onto each daughter cell–DNA must be accurately duplicated

before cell division• Mitosis: paired chromatids separate

and move to opposite ends of the cell• Cytokinesis: cytoplasm + organelles

divide into roughly equal halves

http://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swf

Mitosis Animation

MITOSIS/ CELL DIVISION

• Stages include:

• Prophase

• Metaphase

• Anaphase

• Telophase

Mitosis

Centromeres align at cell’s

equator

Nucleolus disappears;

Nuclear envelope breaks down

Microtubules attach to

Centromeres

Chromosomes condense and

shorten

Centrioles begin to move apart;Spindle forms

Duplicated chromosomes

remain elongated

Centrioles have also been duplicated

LateLateInterphaseInterphase

EarlyEarlyProphaseProphase

LateLateProphaseProphase MetaphaseMetaphase

Mitosis:Spindle fibers pull

chromatids to opposite poles

Chromatids become

independent chromosomes

Chromosomes begin unwinding

Nuclear envelope re-

forms, spindle fibres disappear

Cytoplasm divided along

equator

Each daughter gets 1 nucleus &

half of cytoplasm

AnaphaseAnaphase TelophaseTelophase CytokinesisCytokinesisNextNext

InterphaseInterphase

Prophase• Chromatin condenses

(into chromosomes)• Chromosomes appear

as “X”s.• Nuclear envelope

dissolves (DNA free in cell)

• Animals cells only: Centrioles move to opposite ends of cell + form spindle fibers

• Centromere attaches to spindle fibre

Metaphase

• Each chromosome lines up in the middle of the cell.

• Highly organized so that both cells get exactly the same DNA.

• Spindle fibers attached to centromeres of chromosomes

Anaphase

• Each pair of chromatids splits at the centromere

• Each chromatid is now an individual chromosome

• Paired chromosomes are pulled to opposite ends by spindle fibres

Telophase

• Chromosomes end up at separate poles, spindle fibers begin to dissolve.

• New nuclear envelope begins to form around chromosomes

• chromosomes begin to uncoil

• Cell starts to pinch off through cytokinesis

Cytokinesis• Division of all the

rest of cell parts but not equally (organelles)

• Animals: cell membrane pinches to form two cells

• Plants: new cell plate created between the two cells (becomes cell wall)

The Cell Cycle: An Overview

1)Interphase

2)Mitosis

a) Prophaseb) Metaphasec) Anaphased) Telophase

3)Cytokinesis

Cell Division (Cell Reproduction) = mitosis + cytokinesis

Use an Acronym

For Mitosis: • Prophase = P• Metaphase = M• Anaphase = A• Telophase = T

Make a sentence: • Please Meet At Ten• Phil, Mary, And Tom

Figure 11-2

Links

• http://en.wikipedia.org/wiki/Trisomy#Trisomy

• http://www.medgen.ubc.ca/wrobinson/mosaic/mos_how.htm

Mitosis Drawing• Fold a large sheet of paper in 3

– You should have 3 columns on the front and 3 on the back

• You will draw a cell in each stage of mitosis and include a written description of what is occurring at each stage

• Stages: Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

• Notice that there are 6 stages and 6 coulmns on your sheet...1 stage per column!

Some facts• 500,000 deaths per year (more males)

• Older age group stricken more often

• More than 100 types of cancer, many due to mutations triggered by environmental factors

• Highest cancer incidence: male - prostatefemale - breast

• Highest cancer deaths: lung

Normal cells in culture

• Organized structure

• Limited cell growth

• No overlapping

Cancer cells in culture

• Disorganized• Overlapping

structure• Uncontrolled cell

growth

Some images to make this real: look first at normal skin

Cancerous Skin

What causes a normal cell to become a cancer

cell?