Cell Cycle
Cell Growth and Cell Division
Cell division is strictly controlled by specialized proteins in the nucleus. Your cells continue to divide as
you continue to grow. Your body continues to replace cells that take a lot of wear and tear such as
skin cells, stomach cells and intestinal cells. Cells such as muscle and nerve cells usually do NOT
continue to divide in an adult, but continue to carry out functions necessary for survival
The Cell Cycle
- 3 stages known as the cell cycle:
1) Interphase - cells carry out the functions necessary for survival and cells that divide prepare for
reproduction
2) Mitosis - divides the duplicated contents of the cell's nucleus into two equal parts
3)Cytokinesis - separates the two nuclei and cell contents into two daughter cells
http://www.youtube.com/watch?v=diXoAgH3LMk
Interphase
Longest stage in the cell cycle. Cells carries out its various functions within the organism. Also, the cell
roughly doubles everything in its cytoplasm
Growth and Preparation (G1)
- this is the first phase of interphase, and a cell increases in size and
makes the proteins and molecules necessary for the cell to survive. Some organelles begin to
duplicate
Replication (S): DNA copies or makes a "replica" of itself by:
1) Enzymes separate the DNA by unwinding and the steps of the DNA ladder break apart.
2) Each side then becomes a pattern or template on which a new side forms (remember A -T, and CG)
3) results in two new DNA that have the same sequence of bases as the original DNA. (Identical
genetic information)
http://www.youtube.com/watch?v=zdDkiRw1PdU
Growth and Preparation (G2)
- after DNA replication, the cell continues to grow and makes
materials such as proteins for the new cells. These cells are referred to as "daughter cells". The
chromatin is loosely coiled to allow for production of RNA so that proteins can be made in
preparation for cell division. During this final phase of interphase important organelles such as
mitochondria and chloroplasts are duplicated.
Mitosis
Usually the shortest stage. The process in which the contents of a cell's nucleus divides. Results in two
daughter nuclei, each with the same number and kinds of chromosomes as the original cell. (usually
identical). DNA molecules join together to from the sister chromatids of chromosomes, joined
together by centromere.
Phases of Mitosis:
1) Prophase
-chromosomes coil up into X-shaped.
- nucleolus will disappear, and the nuclear membrane will begin to break
down & eventually disappear
-spindle fibres, tube-like structures made of protein
-centrioles are organelles that "organize" spindle fibres. Centriols begin to
move to opposite sides of the cell.
-chromosomes attach to the spindle fibres at their centromeres
2) Metaphase
-spindle fibres (now completely formed) pull the X-shaped chromosomes
into a single line across the middle (or equator) of the cell.
3) Anaphase
-spindle fibres begin to pull the centromere apart, allowing the sister
chromatids to move to opposite poles of the cell.
-once separate, each sister chromatid is considered to be a chromosome
4) Teleophase
-spindle fibres begin to disappear
-nuclear membrane forms around each set of chromosomes
- Nucleolus appears within each nucleus
- Chromosomes lengthen and get thinner
-with two nuclei the cell is ready to divide
http://www.youtube.com/watch?v=diXoAgH3LMk
Cytokinesis
Final stage of a cell cycle:
Separates the two nuclei into two daughter cells. The new cells are identical to the original parent
cell. In animal cells, the cell membrane pinches together to divided the cells' cytoplasm and
organelles. In plant cells, a cell plate forms along the centre of the cell to divide the cell (Cell Wall)
Checkpoints in the cell cycle
Activities within the cell during the cell cycle are monitored and controlled at specific stages or
checkpoints-special proteins at these checkpoints monitor cell activivies and send this information to
the nucleus. The nucleus then instructs the cell whether or not to divide.
Cell will not divide if: a) There are not enough nutrients to support cell growth b) DNA within the
nucleus has not been replicated c) DNA is damaged
Cancer
Remember that mutagens such as UV rays, can cause gene mutations. If a mutation occurs in a
gene producing the instructions for a checkpoint protein, cell cycle control will be lost. As a result, a
damaged cell may have uncontrolled cell division which is known as the disease Cancer.
KEY: Cancer cells have damage to their checkpoints, so regardless if their DNA is damaged, or if
these cells begin to disrupt functions of nearby cells, cancer cells continue to divide and grow.
Example 1-Healthy cells grow in a single layer and stop dividing when they receive messages from
neighboring cells. Cancer cells do not respond and grow in multiple layers disrupting the function of
nearby cells.
Example 2: DNA are damaged, but continue to divided. Resulting in damaged chromosomes
which is shown by large, abnormal nuclei.
Example 3. Since DNA is damaged, they do not produce the proper protein
for cell function, so
a cancer cell formed in your lungs does NOT function as a lung cell
-Cancer cells can still receive nutrients from nearby blood vessels. So they continue to grow and
divided even more rapidly to form tumours.
- Cancer cells can spread to other areas of your body if tumour cells break away and are carried by
the blood vessels to new locations.