3.D.1 Cell Communication Reflects Shared Ancestry Cell communication processes share common features that reflect a shared evolutionary history.

Communication involves transduction of signals from other cells, organisms, or the environment. Steps of Signal Transduction: Reception Transduction Response

In signal transduction, a ligand binds to a protein receptor on the cell membrane. That signal is then transformed into a signal inside the cell, which produces a specific cellular response.

Signals can be stimulatory or inhibitory.

Signal transduction processes are generally under strong selective pressure.

In single-celled organisms, signal transduction pathways influence how the cell responds to its environment.

Example: In quorum sensing, microbes use chemical messengers to communicate with other nearby cells and to regulate specific pathways in response to population density.

Example: Response to external signals by bacteria that influences cell movement.

In multicellular organisms, signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole.

Example: Epinephrine stimulation of glycogen breakdown in mammals Example: Epinephrine stimulation of glycogen breakdown in mammals. (Model of a G-protein Receptor)

Glycogen is a polysaccharide made from branching chains of glucose. Glucose is stored as glycogen predominantly in liver and muscle cells. Glycogen functions as a long-term form of energy storage of carbohydrates.

 Muscular activity or its anticipation leads to the release of epinephrine (adrenaline) from the adrenal medulla. Epinephrine stimulates glycogen breakdown in muscle and, to a lesser extent, in the liver (the liver is more responsive to glucagon).

The signal molecule epinephrine (ligand) binds to a specific receptor in the plasma membrane.

When the ligand binds, the receptor changes conformation When the ligand binds, the receptor changes conformation. This activates a G protein bound to the receptor. The activated G protein detaches when GDP is replaced by GTP.

The G protein activates the transmembrane protein adenylate cyclase The G protein activates the transmembrane protein adenylate cyclase. Adenylate cyclase catalyzes the formation of the secondary messenger cAMP from ATP.

Cyclic AMP (cAMP) activates a protein kinase, which stimulates a phosphorylation cascade that amplifies the hormone signal.

A protein kinase adds a phosphate group: phosphorylation. A protein phosphatase removes a phosphate group: dephosphorylation.

Cellular response: glycogen is broken down into glucose.

Learning Objectives: LO 3.31 The student is able to describe basic chemical processes for cell communication shared across evolutionary lines of descent. [See SP 7.2] LO 3.32 The student is able to generate scientific questions involving cell communication as it relates to the process of evolution. [See SP 3.1] LO 3.33 The student is able to use representation(s) and appropriate models to describe features of a cell signaling pathway. [See SP 1.4]