DNA and Cell Division
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Transcript of DNA and Cell Division
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?