Cell Growth and Division

Breaking Down the Definitions• Cell division• Chromatid• Centromere• Interphase• Cell cycle• Mitosis• Prophase• Centriole• Spindle• Metaphase

• Anaphase• Telophase• Cytokinesis• Homologous• Diplois• Haploid• Meiosis• Tetrad• Crossing-over

Cell Division•Before a cell becomes too large it divides and forms to DAUGHTER Cells. This process is called CELL DIVISION (or reproduction).

•Cell Division Video CLip

The Chromosome

•During cell division the cell’s DNA is coiled compactly into a CHROMOSOME

•Each chromosome is a single DNA molecule

•The DNA wraps tightly around a protein called HISTONE (helps maintain the chromosome’s shape)

Anatomy of a Chromosome• Each half of a chromosome is

called a CHROMATID• Chromatids form as the DNA

copies itself before cell division• The 2 Chromatids are attached at

a point called a CENTROMERE• CHROMATIN=less tightly areas of

DNA between cell divisions

Chromosome Numbers• Every species has a certain number of

chromosomes in each cell.• Animal chromosomes are either:

• Sex Chromosomes—will determine the gender of an organism (X and Y)

• Autosomes—all of the other chromosomes

• Cells with 2 sets of Chromosomes are DIPLOID

• Cells with one set of chromosomes are HAPLOID (sex cells…half the number of chromosomes)

Chromosomes Clip• How many chromosomes does a potato have?

• How many chromosomes do Ferns have?

• After the video…in your own words why do different organisms have different numbers of chromosomes??

The Cell Cycle•The CELL CYCLE is the repeating events of the life of a cell.

• Interphase is the period between cell divisions

Interphase occurs before mitosis begins

• Chromosomes are copied (# doubles)• Chromosomes appear as threadlike coils (chromatin) at the

start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase

CELL MEMBRANENucleus

Cytoplasm

InterphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Prophase 1st step in Mitosis

• Mitosis begins (cell begins to divide)• Centrioles (or poles) appear and begin to move to opposite

end of the cell. • Spindle fibers form between the poles.

CentriolesSister chromatids

Spindle fibers

ProphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Spindle fibers

Centrioles

Metaphase 2nd step in Mitosis

•Chromatids (or pairs of chromosomes) attach to the spindle fibers.

Centrioles

Spindle fibers

MetaphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Anaphase 3rd step in Mitosis

•Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell.

Centrioles

Spindle fibers

AnaphaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Telophase 4th step in Mitosis

• Two new nuclei form. • Chromosomes appear as chromatin (threads rather than

rods).• Mitosis ends.

NucleiNuclei

Chromatin

TelophaseAnimal Cell Plant Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Cytokinesisoccurs after mitosis

•Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes.

REMEMBER!InterphaseProphaseMetaphaseAnaphaseTelophaseCytokinesis

IPMATC

I P___ M___ A___ T___ C______

Label it!

Brainpop Mitosis

Stages of Mitosis Animation

It’s your turn! Identify the stages of mitosis…

Mitosis Dance Video

Onion Tips and Whitefish…

View 1 View 2 View 3 View 4 View 5

Whitefish

Onion

Meiosis I (four phases)• Cell division that reduces the chromosome number

by one-half.

• four phases:a. prophase Ib. metaphase Ic. anaphase Id. telophase I

Interphase I

• Similar to mitosis interphase.

• Chromosomes replicate (S phase).

• Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres.

• Centriole pairs also replicate.

Interphase I•Nucleus and nucleolus visible.

nuclear membrane

nucleolus

cell membrane

chromatin

Prophase I• Longest and most complex phase (90%).

• Chromosomes condense.

• Synapsis occurs: homologous chromosomes come together to form a tetrad.

• Tetrad is two chromosomes or four chromatids (sister and nonsister chromatids).

Crossing Over

•Crossing over (variation) may occur between nonsister chromatids

•Crossing over: segments of nonsister chromatids break and reattach to the other chromatid.

Crossing Over - variation

nonsister chromatids

chiasmata: site of crossing over

variation

Tetrad

Metaphase I• Shortest phase

• Tetrads align on the metaphase plate.

• INDEPENDENT ASSORTMENT OCCURS:1. The random separation of the homologous chromosomes---this results in GENETIC VARIATION

Metaphase I

metaphase plate

OR

metaphase plate

Anaphase I• Homologous chromosomes separate and move towards the poles.

• Sister chromatids remain attached at their centromeres.

Anaphase I

Telophase I

• Each pole now has haploid set of chromosomes.

• Cytokinesis occurs and two haploid daughter cells are formed.

Telophase I

Meiosis II• No interphase II

(or very short - no more DNA replication)

• Remember: Meiosis II is similar to mitosis

Prophase II• same as prophase in mitosis

Metaphase II• same as metaphase in mitosis

metaphase platemetaphase plate

Anaphase II• same as anaphase in mitosis• sister chromatids separate

Telophase II

• Same as telophase in mitosis.

• Nuclei form.

• Cytokinesis occurs.

• Remember: four haploid daughter cells produced.

gametes = sperm or egg

Telophase II

Meiosis I

Draw This!

Meiosis II

DrawThis!

Meiosis

Cells Dividing Clip

Meiosis Pipe Cleaner Lab

Snowball Fight!