the cell cycle every hour, approximately 1 billion of your cells die – but approximately 1 billion...

The Cell Cycle and The Cell Cycle and MitosisMitosis

The Cell Cycle

• Every hour, approximately 1 billion of your cells die – but approximately 1 billion cells are created in a process of cell division called mitosis.

Why Do Cells Divide?

Why Do Cells Divide

1. Healing and Tissue Repair• An average human looses 105 pounds

of dead skin cells in their life• Every second, millions of your body cells

are injured or die and must be replaced• Replacement of dead cells also occurs

in plants

Why Do Cells Divide

2. Growth• All plants and animals begin life as a

single cell• Only two ways for an organism to grow:

1) single cell gets bigger; or 2) the single cell divides into more cells

Why Do Cells Divide

• One of the most important jobs of a cell is to exchange materials with its environment (the body or outside world)

• The cell needs to get food and nutrients in and waste out

Why Do Cells Divide

• Why Don’t Cells Just Keep Getting Bigger?• Eventually a cell will reach a size where it will

not be able to get enough exchange of materials to sustain cell function

Why Do Cells Divide

3. Perpetuate Life• Important for unicellular (prokaryotes)

organisms like bacteria – creates 2 new organisms

Why Do Cells Divide

3. Perpetuate Life• Also essential for reproduction of

multicellular organisms

The Cell Cycle

The repeating cycle in the life of a cell

Interphase : when a cell is preparing for cell division; this is the majority of the time

Cell division : the process of 1 cell dividing into 2 cells Mitosis: division of the nucleus Cytokinesis : division of the cytoplasm

Interphase

• First Growth Phase (G1)

• Period of growth for a cell• Produces new proteins and organelles

• Synthesis Phase (S)• Cell synthesizes entire copy of DNA

• Second Growth Phase (G2) – shortest phase

• Cell produces organelles and structures for cell division

Mitosis:What is it basically?

• DNA copies (chromosomes) are separated & sorted into two sides of the cell

• the cell then splits in two and part of each parent is carried to the two new cells.

• each ‘daughter’ cell is identical to the parent cell

• results in cells such as internal organs, skin, bones, blood, etc.

Mitosis animation: http://www.youtube.com/watch?v=2WwIKdyBN_s&feature=related

Interphase occurs just before

Mitosis begins:

DNA is replicated along with organelles and other cellular components and the cell prepares for division.

http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm

Before Mitosis :Interphase

Animal cell Plant cell

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

1st step in Mitosis: Prophase (preparation phase)

http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm

•the DNA recoils, and the chromosomes condense•the nuclear membrane disappears•mitotic spindles begin to form.

Mitosis Prophase

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

Animal cellAnimal cell Plant cellPlant cell

2nd step in Mitosis:Metaphase (organizational phase)

• spindle fibres attach to the chromosomes at the centromere

• chromosomes line up the middle of the cell

http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm

Mitosis Metaphase

Animal cell Plant cell

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

3rd step in Mitosis: Anaphase (separation phase)

• the chromosomes split at the centromere

• the ‘sister ‘chromatids are pulled by the spindle fibers to opposite poles of the cell.

http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm

Mitosis Anaphase

Animal cell Plant cell

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

4th step in Mitosis: Telophase

• the chromosomes, the cytoplasm and organelles divide into 2 portions. 

• this diagram shows the end of telophase.

http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm

Mitosis Telophase

Animal cell Plant cell

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

After Mitosis:

Cytokinesis

• the actual splitting of the daughter cells into two separate cells is called cytokinesis

• occurs differently in

both plant and animal

cells.

Beginning of cytokinesis in a plant:

Beginning of cytokinesis in an animal:

http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab6.htm

MITOSIS

Mitosis

• http://www.youtube.com/watch?v=2WwIKdyBN_s&feature=related

• http://www.youtube.com/watch?v=VlN7K1-9QB0

• http://www.cellsalive.com/mitosis.htm

• http://www.sci.sdsu.edu/multimedia/mitosis/mitosis_gif2.html

• http://www.teachersdomain.org/resource/tdc02.sci.life.stru.dnadivide/

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

Your task will be to identify the structures that will allow you to identify each phase and then to observe mitosis in a prepared slide of an onion root tip.

The Cell Cycle

• Remember iPMATc

• Interphase

• Mitosis• Prophase• Metaphase• Anaphase• Telophase

• Cytokinesis

Homework

1. Describe the events in the cell cycle.

2. Explain how mitosis ensures genetic continuity.

3. How does mitosis make the growth and repair of cells possible in an organism?

4. Get a textbook and describe each phase of mitosis along with a picture (pg. 30-32)

• Also define cytokinesis and apoptosis