Control of the Cell Cycle Cell Signaling and

Control of the Cell Cycle, Cell Signaling and Cancer Chapter 10 Section 9. 3 & Chapter 5 Section 5. 6 Biology In Focus AP Biology 2014 Ms. Eggers

Frequency of cell division varies

The cell cycle is controlled by molecular signals in the cytoplasm n n Fusing a cell in mitosis with a resting cell causes the resting G 1 cell to enter that specific stage of mitosis Conclusion?

Cell cycle control system n n = A cyclically operating set of molecules in the cell that both triggers and coordinates key events of the cell cycle A check point is a control point where stop and go signals regulate the cell cycle

Checkpoints

Three main checkpoints to know: n n Damage to DNA and other external factors are evaluated at the G 1 checkpoint; if conditions are inadequate, the cell will not be allowed to continue to the S phase of interphase. G 1 checkpoint is a restriction checkpoint = a stop light The G 2 checkpoint ensures all of the chromosomes have been replicated and that the replicated DNA is not damaged before cell enters mitosis. The M checkpoint (also called the spindle checkpoint) determines whether all of the sister chromatids are correctly attached to the spindle microtubules before the cell enters the irreversible anaphase stage. Source: Boundless. “Regulation at Internal Checkpoints. ” Boundless Biology. Boundless, 14 Nov. 2014. Retrieved 18 Nov. 2014 from https: //www. boundless. com/biology/textbooks/boundless-biology-textbook/cellreproduction-10/control-of-the-cell-cycle-89/regulation-at-internal-checkpoints-398 -11625/

Checkpoint signal molecules n Regulatory proteins & protein complexes: n n Kinases: enzymes that regulate other proteins by phosphorylating them (adding a phosphate can activate or inactivate) Cyclins: proteins that control progression through the cell cycle by activating cyclindependent kinases

Levels of cyclins during cell cycle stages

Cyclins activate CDKs which activate other proteins

Maturation-promoting factor (abbreviated MPF) n n Maturation-promoting factor (abbreviated MPF, also called mitosis -promoting factor or M-Phasepromoting factor) is a protein composed of cyclin B and cyclindependent kinase (CDK 1) that stimulates both mitosis and meiosis. MPF promotes the entrance into mitosis (the M phase) from the G 2 phase by phosphorylating multiple proteins needed during mitosis.

Let’s back up and talk about cell signaling…

Signal molecule = message n The chemical messenger sent out by one cell that elicits a response in another cell. Can be large such as a protein growth factor, a steroid hormone such as estrogen, a small neurotransmitter such as acetylcholine which stimulates muscles to contract, and even something as small as the gas nitric oxide (NO).

Receptor = receiving end n n The signaling molecule is a ligand, which is a molecule that binds to and interacts specifically with another molecule. The molecule to which a signaling ligand binds is called a receptor. Receptors can be integral membrane proteins OR located within the cytoplasm n Only cells with the ligand-specific receptor will respond to the signal = VERY SPECIFIC n

How does a cell ‘hear’ a message? The signal transduction pathway Signal Receptor Relay molecules Activation

Where can receptors be located?

How might a target cell respond? n n n Ligand might open a protein channel in the membrane directly by changing the conformation (shape) of the receptor – ion channel receptors Ligand might bind to a receptor in the cytoplasm that then travels to the nucleus and changes gene expression – steroid hormone receptors Ligand might activate a secondary messenger such as a kinase (an enzyme that phosphorylates another protein, thereby changing its activity) -- G protein-coupled receptors, receptor tyrosine kinases, etc.

Ion channel receptors

Steroid hormone receptors

G-protein coupled receptors

G protein coupled receptor & c. AMP second messenger: AMPLIFICATION

Cell signaling can (and often does) result in changes in gene expression in the target cell

A growth factor is a protein released by certain cells that stimulates other cells to divide.

A VERY common method for activating and inactivating important proteins is by phosphorylating them A kinase is an enzyme that adds a phosphate group to another protein.

Now, back to the cell cycle. Message from outside the cell can activate a signal transduction pathway that turns on the genes that make cyclins. The cyclin proteins made from these genes can then turn on the cell cycle & cells begin to divide…

Wound Responding cells send out signal molecules that tell nearby cells to start dividing for tissue repair. Cell cycle is activated.

Cancer = unregulated cell division happens when cells divide out of control

Just as there are signals to tell cells to divide, there also signals that tell cells to NOT divide n n Density-dependent inhibition: a phenomenon in which crowded cells stop dividing Adjoining cells send a cell division-inhibiting signal to their neighbors n Anchorage dependence: Most cells must be attached to a substratum (some sort of surface or extracellular matrix) in order to divide

Cancer cells do not show density-dependent inhibition, anchorage dependence and don’t require growth factors

Cancer vocabulary n n n Transformation: the term for when a normal body cell mutates to become a cancer cell A benign tumor is composed to abnormal cells that proliferate but do not have the capacity to spread and invade other tissues A malignant tumor is made up of cancer cells that proliferate out of control and can spread to new tissues (called metastasis). Cancer is the disease caused by malignant tumors.

Question n Lectins are naturally occurring plant proteins that help promote increased mitosis within plant root tips. These proteins influence the normal production of MPF within the root cells and thereby speed up the cell cycle. In no more than three sentences, state ONE similarity and TWO differences between Lectin influenced cells and cancer cells.

n Cancer and the cell cycle animated tutorials