The Cell Cycle and Cancer

AP Biology

Cell Cycle• Numerous genes control the cell cycle• They regulate the progression through checkpoints. A sensor

detects faulty or incomplete cell cycle events such as DNA damage. A signal is sent from the sensor to an effector that can stop the cell cycle until the problem has been resolved.

Checkpoints

What does the controlling?• Kinases are enzymes

that add phosphate groups to proteins (phosphorylation)

• There are over 500 of these kinases

• They take phosphates from ATP and transfer them to proteins, changing the shape (and function)

What does the controlling?• Often, kinases are

present, but they must be activated by attaching to a cyclin, another protein. These kinases are called cyclin-dpendent kinases, or Cdks. A Cdk and it’s cyclin are referred to as a cyclin-Cdk complex.

What does the controlling?• They are the core of

cell cycle control, triggering or turning off activities.

• The concentrations of Cdk and cyclin usually rise and fall together in the cell.

• This system keeps the cell from dividing when it should not divide

What is cancer?

• Cancer is the inappropriate proliferation of cells

• If the cell checkpoints are not in place, this inappropriate proliferation can occur.

• Too much mitosis! • Forms a mass or tumor

What causes cancer?

• Mutations in the genes encoding the proteins that control the cell cycle. (genes that code for the kinases and cyclins)

• Oncogenes: genes that have a normal function, but that when mutated, may cause cancer.

Oncogenes

What causes cancer?

• Oncogenes may be altered by mutagens such as UV light, chemicals, radiation, viruses, or a genetic predisposition

• Typically dominant, meaning only one of your two genes must be mutated to cause the altered cell functions

What causes cancer?

• Tumor Suppressor genes: can halt progression of the cell cycle.

• If these are mutated, cells divide when they should not

• BRCA I is a gene that produces a protein that works with other proteins to repair DNA damage. (a type of tumor suppressor)

Usually takes a hit in both types of genes ( and their resulting proteins to cause cancer.

Tumor Suppressor Genes