Cell Division
By: Amber Tharpe
Activation
Humans make 2 trillion new cells per day
Cell Cycle2 main parts
Interphase- Cell is normal
Mitosis- Cell is dividingCytokinesis- occurs at the end of mitosis
Interphase
When cell is not dividingCell spends 90% of its life
hereDNA is called chromatin and
is not condensedDNA and organelles double
to prepare for cell division
Interphase has 3 parts:
1. Gap1(G1)- cell carries out normal functions and doubles organelles at the end
2. Synthesis (S)- DNA is doubled3. Gap 2 (G2)- additional cell growth
Different types of cells divide at different rates
G0- stage where cell performs normal functions but does not divide
Cell must have an adequate surface area to volume ratio to contain all the necessary organelles and molecules but still get nutrients in and wastes out
Cancer
Uncontrolled cell growth
Continuous mitosis without interphase
Benign- harmless cancer cells that remain clumped together
Malignant- harmful cancer cells break away
Metastasize- when cancer cells break away and form tumors elsewhere
Carcinogens- substances that promote the development of cancer Ex: UV light and air pollutants
Chromosome Structure
Chromosome- long thread of DNA with numerous genes; Condensed and looks like an X
Histones- proteins that DNA wraps around Chromatin- loose DNA that is not condensed Chromatid- half of a duplicated chromosome Centromere- region where sister chromatids are held
together Telomeres- ends of DNA with repeating nucleotides
without genes; short section is lost each time DNA is copied
MitosisDivides DNA into 2 nucleiMakes 2 daughter cells with a diploid number
Used for growth and repair
Also used in some asexual reproduction
4 stages (P-M-A-T)
1. Prophase2. Metaphase3. Anaphase4. Telophase
Stages of Mitosis (P-M-A-T)
Interphase Early Prophase
Metaphase
Early Anaphase
Prophase
AnaphaseTelophase
http://micro.magnet.fsu.edu/micro/gallery/mitosis/mitosis.html
ProphaseDNA condensesNuclear envelope dissolves
Spindle fibers start to form
Prophase(in animal cell and onion cell)
MetaphaseChromosomes align in the equator (middle) of the cell
Spindle fibers attach to the chromosomes to move them
AnaphaseSister chromatids separate to opposite poles
Spindle fibers split chromosomes at the centromere, forming sister chromatids
Telophase 2 nuclear envelopes form
around the separated DNA Spindle fibers dissolve In animal cells
Cell membrane pinches in (cleavage furrow)
In plant cellsCell plate forms which later
becomes 2 cell walls
CytokinesisCytoplasm and organelles divide
2 cells form
http://www.classzone.com/cz/books/bio_07/get_chapter_group.htm?cin=2&rg=animated_biology&at=animated_biology&var=animated_biology
Animation of Stages of Mitosis
http://biology.about.com/library/blmitosisanim.htm
Asexual Reproduction
1 parentOffspring is identical to parent
Less genetic diversity
Binary FissionAsexual reproduction for bacteria
DNA is copied in 1 cellThe cell divides into 2 cells with the same DNA
Binary Fission
Other Types of Asexual Reproduction
Budding - a small projection form on the parent with forms a new organism ex: hydra and yeast
Fragmentation - when a parent splits into pieces, each piece is a new organism ex: flatworms and sea stars
Vegetative reproduction- when new plants form from runners Ex: some grasses
http://www.classzone.com/cz/books/bio_07/get_chapter_group.htm?cin=2&rg=animated_biology&at=animated_biology&var=animated_biology
ChromosomeLong thread of DNA containing many genes
X- shaped
Somatic cells Body cells All cells not involved in
reproduction Diploid cells (2N)
Contains 2 copies of each chromosome
In humans 46 chromosomes Made by mitosis
Gametes Sex cells Egg (female) or sperm (male) Haploid cells (1N)
Contains 1 copy of each chromosome
In humans 23 chromosomes Made by meiosis Used in sexual reproduction
AutosomesChromosome pairs 1-22
Sex ChromosomesChromosome pair 23 for gender
Either X or YXX is femaleXY is male
Sexual Reproduction
Offspring are a mixture of both parents
Occurs by meiosis then fertilization Meiosis
Formation of gametesMakes haploid cells from diploid
cells Fertilization
The actual fusion of the 2 gametesFirst cell is called a zygote
Asexual Reproduction
Sexual Reproduction
advantages 1 parent, requires less energy, fast
Increases genetic diversity, increasing the ability to adapt
disadvantages Decreases genetic diversity,Less likely to adapt
2 parents, requires more energy, slow
MeiosisProcess of making gametes for sexual reproduction
Events that occur during meiosis allows for greater genetic diversity
Meiosis Meiosis I
Makes 2 unique diploid cellsProphase I – Telophase I
Interphase without duplicating DNA
Meiosis IIMakes 4 unique haploid cellsProphase II – Telophase II
Prophase ISimilar to prophase in
mitosiscrossing over occurs
homologous chromosomes line up and sections of the chromosomes overlap and become incorporated into the other
Allows for genetic diversity
Metaphase I
Homologous chromosomes pair up at the equator- 2 lines of chromosomes in the middle
Independent Assortment Allows for genetic diversityWhen homologous chromosomes
line up in the middle, some chromosomes from the mother and father line up on either side
Anaphase I
Homologous chromosomes separate to opposite poles
Sister chromatids remain together (looks like W’s)
Telophase I
Similar to telophase in mitosis Makes 2 cell with unique
combinations of chromosomes At the end of Meiosis I, 2 diploid
cells that are genetically unique are formed
What Makes Meiosis I Different from Meiosis II? Between telophase I and prophase II-
DNA is not replicated
Prophase II
Similar to prophase in mitosis DNA was not doubled Only one copy of each chromosome Starting with half the DNA of
prophase I
Metaphase II
Chromosomes line up in the middle- single file line
Half the chromosomes of Metaphase I
Anaphase II
Sister chromatids are pulled to opposite poles
Half the chromatids of Anaphase I
Telophase II Produces 4 haploid cells with
unique combinations of chromosomes
Females produce 1 ovum (egg) and 3 polar bodies
Males produce 4 sperm cells