POD

• Compare and contrast asexual and sexual reproduction.

• What do you think triggers cells to divide?– Give reasoning for your predictions

The structure of eukaryotic chromosomes

The Relationship between Chromosomes, DNA and Genes • DNA –

deoxyribose nucleic acid

• macromolecule, carries genetic information

– A gene is a short section of DNA

http://www.hhmi.org/biointeractive/dna-packaging

• DNA is tightly packed in the nucleus of every cell.

• DNA wraps around special proteins called histones

• which form loops of DNA called nucleosomes.

• These nucleosomes coil and stack together to form fibers called chromatin.

• Chromatin in turn forms larger loops and coils to form chromosomes.

TERMS YOU NEED TO KNOW:

Structure of a Chromosome

Chromosome Numbers• Sex chromosomes - determine the sex of an

organism

• Autosomes - All other chromosomes in an organism

Somatic Cells (body cells) –

- 2 Sex chromosomes X or Y

- all other chromosomes are autosomes

Gametes (Sex cells)

- half the number of chromosomes as a somatic cell

- 1 sex chromosome

- all other chromosomes are autosomes

Example: Humans• Somatic cells have 46 chromosomes

– 2 sex chromosomes• women have two X chromosomes

• men have an X and a Y

– 44 autosomes

• Gametes– 1 sex chromosome– 22 autosomes

Chromosome Numbers• Haploid and diploid are terms referring to the number of

sets of chromosomes in a cell.

• diploid cells (2n) - Somatic cells (body cells), contains two complete sets of chromosomes

– every organism has a characteristic diploid number

• haploid cells (n) - Gametes (sex cells) have only one complete set of chromosomes

– the length and number of chromosomes is unique to each species of organism.

Organism

• Carrot

• Cat

• Chimpanzee

• Dog

• Earthworm

• Goldfish

• Lettuce

Chromosome Number

• 18

• 32

• 48

• 78

• 36

• 94

• 18http://www.ncbi.nlm.nih.gov/mapview/

Mactching sets of chromosomes in a diploid cell are

called homologous chromosomes. Both chromo in a

homologous pair contain information that code the

same trait (genes).

Example of trait: Eye color

Are sex chromosomes homologous? Why or Why not?

Cell Division and Reproduction PBS : How Cells divide

http://www.pbs.org/wgbh/nova/baby/divide.html#

Prokaryotic chromosomes

• Lack true nuclei

• DNA found in cytoplasm

• Most contain a single, circular DNA chromosome

The Prokaryotic Cell CycleCell Division in

Prokaryotes/Asexual Reproduction• BINARY FISSION is the division of a

prokaryotic cell into 2 offspring cells. (asexual reproduction)

• The cell grows in size.

• DNA replication - The chromosome makes a copy of itself, resulting in two identical chromosomes

• Cytokinesis - The cell splits into two new cells.  Each new cell contains identical genetic information as the original cell

A protozoan undergoes binary fission

Eukaryotic Cell CycleThe stages of life of a cell

• Interphase

• Mitosis

• Cytokinesis

Eukaryotic Cell Cycle

http://highered.mheducation.com/sites/9834092339/student_view0/chapter10/control_of_the_cell_cycle.html

Cell Division in Eukaryotes

• A cell typically goes through stages during its life, growing and developing before it divides into new cells.

• The cell cycle is the repeating events that make up the life of a cell

http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/u4aos1p2.html#Chromosomes

Interphase• Period of normal metabolic activity

– Carries on all usual functions– Increases in size– Synthesizes new proteins and organelles

• DNA Replication – DNA is duplicated (copied)– Reminder: DNA exist as chromatin within the nucleus.

Chromatin are thin uncoiled strands of DNA wrapped around a protein

– allows each new cell will have a complete copy of each chromosomes

• The actual dividing of the cell consists of two steps:

– Mitosis

– cytokinesis

Mitosis• The division of the Nucleus

– Process by which a nucleus divides into 2 identical nuclei

– Mitosis produces two daughter cells that are identical to the parent cell.  If the parent cell is haploid (N), then the daughter cells will be haploid.   If the parent cell is diploid, the daughter cells will also be diploid. 

– N N– 2N 2N– This type of cell division allows multicellular

organisms to grow and repair damaged tissue.

4 phases of Mitosis

Prophase• the chromatin coils (condenses) to form visible chromosomes*

• nucleolus and the nuclear membrane begin to disappear

• centrosomes (centrioles) appear

• Spindle fibers start to form• Centrioles begin to move

to opposite ends

• The chromatin condensed into chromosomes

• each chromosome contains two identical halves called sister chromatids

• The constricted area of each chromatid is called a centromere

Sister chromatids

Centromere

Metaphase• chromosomes are

moved to the center of the cell (equator) by the spindle fibers attached to the centromeres

• The two sister chromatids of each chromosome are attached to spindle fibers from opposite ends of the cell

Anaphase• The sister chromatids

are separated from each other; now considered to be individual chromosomes

• The centromeres of each chromosome are pulled by the spindle fibers toward the opposite ends (poles) of the cell

Telophase• after the chromosomes reach opposite ends of the cell, the spindle fibers breakdown

• the chromosomes return to less tightly coiled Chromatin

• new nuclear envelope begins to form around the chromosomes at each end of the cell – End of mitosis

Nuclear envlopes reappear

Cytokinesis• The cell membrane begins to

pinch the cell in two as cytokinesis begins

• the cytoplasm of a cell and its organelles are equally separated into two daughter cells

• Completes the process of cell division

• the new cells are now in interphase

• Cytokinesis differs between plants and animals

• Plant cells have a rigid cell wall, so the plasma membrane does not pinch in.

• the material for the new cell wall is called the cell plate

• The cell plate and membranes gather and fuse along the equator, between two two nuclei forming two identical cells

Results:

• unicellular organisms remain as single cells

• in multicellular organisms, cell growth and reproduction result in groups of cells that work together as tissue to perform a specific function

• http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/mitosis.html

• http://www.johnkyrk.com/mitosis.html

• http://www.biology.arizona.edu/Cell_bio/tutorials/cell_cycle/cells3.html

• http://biology.about.com/library/blmitosisanim.htm

Normal Control of the Cell Cycle

• Proteins regulate the progress of cell division

• Occasionally, cells lose control of the cell cycle.

• uncontrolled dividing of cells can result from proteins not functioning properly

• cancer is a malignant growth resulting from uncontrolled cell division