chromosomes decondensing nuclear envelope reforming nucleolus reappears pinching of cell membrane at equator
– microfilaments attached to plasma
membrane form a ring around
equator of cell
– ring contracts, like a drawstring,
dividing the cytoplasm
– stiff cell wall makes pinching
– Golgi complex buds off vesicles
filled with carbohydrate
– vesicles line up at equator and
fuse, producing a structure
called the cell plate
– cell plate becomes new cell wall
between the two cells
Mitotic Cell Division Functions:
Growth, maintenance, repair of body
Forms the basis of
Summary of Mitosis
Nuclear envelope disappears
Spindles move to opposite sides of the cell
Spindle fibers attaches to centromeres on the chromosomes
Chromosomes lined up on equator of the cell
Spindles at opposite ends of cell
1 copy of each chromosome is pulled to opposite poles by the spindle
Nuclear envelope reappears
Cytoplasm divided into 2 cells
Cancer is a disease of uncontrolled cell division. It starts with a single cell that loses its control mechanisms due to a genetic mutation. That cell starts dividing without limit, and eventually kills the host.
Normal cells are controlled by several factors. They stay in the G1 stage of the cell cycle until they are given a specific signal to enter the S phase, in which the DNA replicates and the cell prepares for division. Cancer cells enter the S phase without waiting for a signal.
Another control: normal cells are mortal. This means that they can divide about 50 times and then they lose the ability to die. This “clock” gets re-set during the formation of the gametes. Cancer cells escape this process of mortality: they are immortal and can divide endlessly.
A third control: cells that suffer significant chromosome damage destroy themselves due to the action of a gene called “p53”. Cancer cells either lose the p53 gene or ignore its message and fail to kill themselves.
There are many different forms of cancer, affecting different cell types and working in different ways. All start out with mutations in specific genes called “oncogenes”. The normal, unmutated versions of the oncogenes provide the control mechanisms for the cell. The mutations are caused by radiation, certain chemicals (carcinogens), and various random events during DNA replication.
Once a single cell starts growing uncontrollably, it forms a tumor, a small mass of cells. No further progress can occur unless the cancerous mass gets its own blood supply. “Angiogenesis” is the process of developing a system of small arteries and veins to supply the tumor. Most tumors don’t reach this stage.
A tumor with a blood supply will grow into a large mass. Eventually some of the cancer cells will break loose and move through the blood supply to other parts of the body, where they start to multiply. This process is called metastasis. It occurs because the tumor cells lose the proteins on their surface that hold them to other cells.
G2 Phase Production of mitosis proteins The Cell Cycle