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

Metaphase

AnaphaseSister chromatids separate to opposite poles

Spindle fibers split chromosomes at the centromere, forming sister chromatids

Anaphase

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

Telophase

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