Cell Communication Part 3

Three Stages of Cell Signaling Reception Signal transduction Response

3. Cellular Response What happens within a cell after the signaling pathway has been completed? Several different types of cellular responses: Secretion of a hormone, synthesis of an enzyme, etc.

Cytoplasmic & Nuclear Responses Response can occur at either level. May cause the opening or closing of an ion channel. Regulates synthesis of enzymes by activation of genes within the nucleus. Initiates or inhibits production of transcription factors

Fine Tuning The Response Multiplicity of pathway signals serves 2 main purposes: Signal amplification Response specificity

Signal Amplification Several steps within the cascade allows for the amplification of product to be made during each step. For example: the pathway of glycogen breakdown produces increasing amounts of product at each step of the pathway.

Specificity of Cell Signaling Different cells in the body are exposed to the same signals, but do not respond to all of them. How are some signals responded to, and others ignored? Some signals act on 2 different kinds of cells but elicit different responses. How can the same molecule elicit different responses?

Specificity For example: Liver cells and cardiac muscle cells are both exposed to epinephrine in the bloodstream. However, epinephrine causes glycogen breakdown in the liver, and cardiac muscle contraction in the heart.

Different Cells = Different Proteins Specificity of response depends on several factors within each cell: Signal receptor proteins Relay proteins Proteins that carry out the cellular response Therefore, different cells will have different responses to the same signal.

Signaling Efficiency Scaffolding proteins Carry several protein kinases, therefore can phosphorylate several proteins at one time. Allows for amplification of cascade. Pathways are not always linear: Several pathways can overlap and intertwine

When Pathways Run Amok When one or more proteins involved in a pathway are damaged or missing, the results can be severe: For example, Wiskott-Aldrich Syndrome (WAS) is characterized by the absence of 1 signal relay protein. Widespread effects: Abnormal bleeding Eczema Susceptibility to infections Leukemia

Signal Termination Signaling pathways should not always be activated. Every step of a cascade is reversible. Works by feedback mechanisms. Positive feedback Negative feedback