All living things are made of cells. Cells grow and divide to make copies of themselves or to produce new cells. Cells divide for three important reasons: Growth, Repair, and Reproduction
1. Growth
Cell division is important to growth. When the cells of an organism divide, the number of cells in the organism increases, making the organism bigger.
Cells can grow to make an organism bigger but cells can only grow to be so big. Cells can only grow so big for two reasons:
As a cell becomes larger, it places a greater demand on DNA. More and more stress is put on DNA and eventually the DNA cannot meet all the cell’s needs.
A large cell has difficulty transporting nutrients into the cell and waste out of it. As a cell becomes bigger, the volume of the cell increases. The cell needs more nutrients and produces more waste. There is not enough surface area (cell membrane) to transport things in and out of the cell fast enough to meet the needs of the cell.
is important to growth.
Cell growth is limited by DNA. As a cell becomes larger, it places a greater demand on DNA. DNA cannot handle the stress associated with a very large cell.
2. Repair
Cells make more copies of themselves to replace damaged cells.
Sometimes cells are damaged due to disease or injury. Sometimes cells die. In order to repair damaged or dead cells, cells divide to replace them.
Example: When you get a cut on your skin, your skin cells divide to make new cells that replace the cells that were damaged or broken.
3. Reproduction
Cell division is important for reproduction - the production of an offspring.
Some organisms - such as unicellular organisms - divide in half to produce offspring identical to the parent (asexual reproduction).
Some organisms use a special form of cell division to form sex cells or gametes which are needed for sexual reproduction.
Cells make more copies of themselves to
The Cell Cycle
The life of a cell is called the cell cycle.
There are two major periods in the cell cycle:
Interphase: A cell spends most of its time in interphase.
Cell Division: A cell divides during cell division. Cell division is a short and quick period. Cell division is also called M phase.
There are major periods in the cell cycle
A cell spends most of its time in interphase.
Cell division is a long period
Interphase
Interphase is divided into 3 phases: G1, S and G2.
G1 Phase: The cell does most of its growing during the G1 phase. The cell increases in size and produce new organelles and proteins.
S Phase: During S phase, the cell’s DNA replicates. S phase is called so because DNA is synthesized during S phase.
G2 Phase: G2 phase is the shortest phase of interphase. During G2, organelles replicate and molecules needed for cell division are produced.
Cell Division (M Phase)
Cell Division or M phase is when cell division takes place.
Cell Division is separated into two parts:
In the 1st part, the nucleus of the cell divides. This is called mitosis.
In the 2nd part, the cytoplasm divides. This is called cytokinesis.
What occurs during G1
Chapter 9: Abnormal Cell Growth
Regulating Cell Growth & Division
Cell growth and division is regulated by proteins. The proteins perform “checks” at the different stages of the cell cycle.
There are two kinds of genes that control cell growth and division:
Proto-oncogenes code for proteins that promote cell growth/division.
Tumor suppressor genes code for proteins that inhibit cell growth/division
In normal cells, proto-oncogenes and tumor suppressor genes are expressed in such a way that the cells grow and divide normally.
Cell division and division is regulated by proteins
What type of protein codes for proteins that inhibit cell growth and division?
Abnormal Cell Growth
Sometimes cells lose the ability to control cell growth and division. This results in a disorder known as cancer. We call cells that grow and divide abnormally or uncontrollably cancer cells.
A mass of uncontrollably or abnormally dividing cells is called a tumor.
There are two kinds of tumors:
Benign tumor are not really considered cancer cells. The cells are abnormal, but they do not invade neighboring tissues and they grow slowly. These tumors can damage neighboring tissue but they do not invade neighboring tissue.
A malignant tumor is made of cancer cells that invade and destroy neighboring tissue. Cancer cells from a malignant tumor metastasize ( or spread) to other parts of the body, forming malignant tumors in other body tissues/organs. Malignant tumors are more dangerous than benign tumors because they invade and metastasize.
Cancer cells are cells that grow and divide abnormally or uncontrollably.
A tumor is made up of cancer cells that invade and destroy neighboring tissue
What causes abnormal cell growth?
Very often, mutations (mistakes) in genes that control cell growth and division cause cancer. Mutations in proto-oncogenes or tumor suppressor genes can produce proteins that do not work and thus, cannot control cell growth and division.
Some substances in the environment can cause mutations in these genes. Radiation (including UV light from the sun), tobacco smoke and asbestos can cause mutations in these genes. They can cause oncogenes to be overexpressed and can cause tumor suppressor genes to be under-expressed or disabled.
Some mutations in genes that control cell growth and division are inherited. For example:
Mutation in tumor-suppressor genes known as BRCA genes are associated with an increased risk for breast and ovarian cancer in females.
Mutations in tumor-suppressor genes known as p53 and PTEN are associated with various types of cancer in both males and females.
Cancer is often caused by mutations in genes that control cell growth and division.
Mutation in genes are associated with an increased risk of breast and ovarian cancer in females.
All living things are made up of
Cells divide for three important reasons: Growth, Repair, and
A large cell has difficulty transporting nutrients into the cell and waste out of the cell
When you get a cut on your skin, your skin cells divide to make new cells that replace the cells that were damaged or broken.
Cell division is important for
Some organisms use a special form of cell division to form gametes which are needed for sexual reproduction.
What occurs during S phase
What occurs during G2
The nucleus divides during
The cytoplasm divides during
A mass of uncontrollably or abnormally dividing cells is called a
What does metastasize mean?