The Eukaryotic Cell Cycle

What controls the cell cycle? Molecules present during the S (DNA synthesis) and M (Mitosis) phase These molecules control the progression of those phases Like receptor proteins, these molecules can be deactivated and are done so during the G1 and G2 phase of cell division.

What is a cell checkpoint? A control point that gives the cell go-ahead signals Aids in cell division regulation These checkpoints include: G1, S, G2, and Mitosis (M phase) Helps in cell division.

What happens at each checkpoint?

G1 Checkpoint This is where the DNA is assessed and prepared for synthesis If conditions are inadequate the cell will not be allowed to continue to the S phase Cytoplasms duplicate

S Checkpoint DNA is Duplicated and Chromosomes are created.

G2 Checkpoint Ensures all of the chromosomes have been replicated and that the replicated DNA is not damaged before the cell enters Mitosis This prepares the cell for mitosis or M phase. Security for cell division Cancers do not go through G2 phase

Mitosis Also known as the M checkpoint or Spindle checkpoint Determines whether all the sister chromatids are attached correctly to the spindle fibers. The cycle will not proceed until the kinetochores of each pair of sister chromatids are firmly anchored to at least two spindle fibers arising from opposite poles of the cell. Finally, cell begins to divide

G₀ Phase It occurs in the cell cycle when the cell is in a quiescent state The call is no longer active Stopped dividing Occurs after Mitosis Referred to as a Postmitotic cell

Protein Kinase A protein kinase is an enzyme that transfers phosphate groups from ATP to a Protein Regulate majority of cellular pathways Especially signal transduction Human genome contains around 500 protein kinase genes Make up about 2% of all human genes Unregulated protein kinases can cause disease and cancers Drugs that inhibit certain protein kinases are in development.

Growth Factors A naturally occurring substance that helps stimulate cell division Usually in the form of a protein or hormone Act as signaling molecules between cells

PDGF stimulation of Fibroblast division. The fibroblasts have PDGF receptors on their plasma membrane The PDGF molecules then bind to these receptors Triggers a signal transduction pathway This then allows the cells to pass the G1 checkpoint and divide.

Density-Dependent Inhibition -the process where crowded cells stop dividing

Normal Cells -Divide until they form a single layer of cells on the inner surface of the culture container. -At which point the cells stop dividing. -Unless some are removed, they then divide until the hole is covered.

Cancerous Cells -Division of cells continues even after the surface of a container has reached the maximum surface area.

Anchorage Dependence -To divide, they must be attached to a substratum, such as the inside of a culture jar or the extracellular matrix of a tissue.

HeLa Cells -HeLa cells’ original source was a tumor removed from a woman named Henrietta Lacks. -This cell line has been reproducing in culture since 1951. -The cell line was found to be remarkably durable and prolific which warrants its extensive use in scientific research

Transformation -Is the conversion of a normal animal cell to a cancerous cell.

Metastasis -Is the spread of cancer cells to locations distant from their original site.

Tumors

Benign Tumors: Benign tumors consist of a mass of abnormal cells that remain at the origin/original site. These cells lack the ability to invade neighboring tissue or metastasize. This makes them non-cancerous.

Radiation Therapy: Definition- treatment of disease using X-rays or other forms of radiation Use in Cancer Therapy: Beam of intense energy target cancerous cells in an effort to kill them. Radiation damages cells by destroying the genetic material that dictates how it grows and divides. Both healthy and cancerous cells are damaged by the therapy, but the goal is to harm the least healthy cells as possible.

Malignant Tumors: Consists of cells growing out of control. The cells have the ability to invade nearby tissues and spread throughout the body, classifying them as cancerous.

Examples of Cancer Therapy:

Chemotherapy: Definition- the treatment of disease with the use of chemical substances Use in Cancer Therapy: Certain powerful drugs, toxic to rapidly dividing cells (cancerous cells), are inserted into the circulatory system. Side effects arise due to the drug affecting the activity of healthy cells along with the cancerous ones.

CANCER https://www.khanacademy.org/science/biology/cellular-molecular-biology/stem- cells-and-cancer/v/cancer Start @ 5 min