5.1 Overview:
The Cell Cycle and Mitosis
• Due to the loss and death of cells, the body must
replace them. A good example of this is human skin cells - each day
millions are shed.
•
The life of a cell is divided
into three stages known as
the cell cycle:
1. Interphase: cell carries out normal
functions
2. Mitosis: nucleus gets duplicated
3. Cytokinesis: the two nuclei split apart
two separate cells are formed
•
Interphase is the cell living everyday life; mitosis and cytokinesis are the cell
reproducing by splitting itself into two… one cell becomes two!
See pages 150 - 153
(c) McGraw Hill Ryerson 2007
More detail about the 3 stages…
1. More detail about Interphase
•
•
Longest stage
Is when a cell performs normal functions and grows
(E.g., a cell in your intestinal lining absorbing nutrients is in interphase)
•
In late interphase, DNA copies itself (called replication).
•
•
Replication involves several steps:
1. The DNA molecule unwinds
with the help of an enzyme.
2. New bases pair with the
bases on the original DNA.
3. Two new identical DNA
molecules are produced.
At the end of interphase, the cell
continues to grow and make proteins, including duplicating its organelles,
in preparation for mitosis and cytokinesis.
See pages 153 - 154
(c) McGraw Hill Ryerson 2007
More detail about the 3 stages…
2. More detail about Mitosis
•
•
The shortest stage
When the nucleus of a cell divides in two
•
•
•
Remember there are now 2 sets of DNA in the cell; one set goes into each nucleus
There are temporarily 2 nuclei in the cell, called the “daughter nuclei”
Occurs in 4 stages:
•
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase.
Starts with:
•
•
the 2 copies of a chromosome (called
“sister chromatids”) partnering up
They are joined together by a centromere.
See pages 155 - 156
(c) McGraw Hill Ryerson 2007
More detail about the 3 stages…
3. More detail about Cytokinesis
•
When the one cell splits into two cells
•
•
•
•
•
The cell membrane pinches together in animal cells
A cell plate forms and divides the cell in plant cells
One nucleus goes into each cell
The cell’s cytoplasm and organelles are split between cells
The two cells formed are called daughter cells
Now you know how cells “reproduce”!
See pages 155 - 156
(c) McGraw Hill Ryerson 2007
What Happens in each Stage of
Mitosis??
To understand what happens, you need to know some definitions.
Use your text to define each word: (first one’s free! )
•
Sister chromatids = two identical copies of a single chromosome
that are connected by a centromere
•
Centromere =
•
Nucleolus =
•
Spindle fibres =
See pages 156 - 157
chromosome
(c) McGraw Hill Ryerson 2007
chromosome
What Happens in each Stage of
Mitosis??
Early Prophase - nucleolus disappears, spindle fibres form from
centrioles (which lie outside nuclear membrane)
Late Prophase – nuclear membrane disappears, spindle fibres attach
to centromeres of chromosomes
Metaphase - chromosomes align on equator of cell
Anaphase - spindle fibres pull sister chromatids to opposite poles of cell
Telophase - spindle fibres disappear, a nuclear membrane re-forms
around each separated set of chromosomes
See pages 156 - 157
(c) McGraw Hill Ryerson 2007
Video:
http://www.youtube.com/watch?v=AhgRhXl7w_g
Lego Version:
*notice when one strand of DNA replicates into 2 sister
chromatids (forming the X-shape)
http://video.mit.edu/watch/lego-animation-of-mitosiswith-descriptive-titles-3077/
(c) McGraw Hill Ryerson 2007