Chapter 11: Cell Communication

Q: What are the three stages of signaling?

A: Signal reception, signal transduction, and cellular response.

Q: What are the three major types of plasma-membrane receptors?

A: They are G protein-coupled receptors, receptor tyrosine kinases, and ion channel receptors.

Q: Are all signal receptors membrane proteins?

A: No, some are proteins located in the cytoplasm or nucleus of target cells. To reach such a receptor, a chemical messenger must be able to pass through the target cell's plasma membrane. A number of important signaling molecules can do just that, either because they are small enough to pass between the membrane phospholipids or because they are themselves lipids and therefore soluble in the membrane.

1. External signals are converted to responses within the cell.

2. Reception: A signaling molecule binds to a receptor protein, causing it to change shape.

3. Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell.

4. Response: Cell signaling leads to regulation of transcription or cytoplasmic activities.

5. Apoptosis (programmed cell death) integrates multiple cell-signaling pathways.

Figure 11.2 Communication between mating yeast

Cells of the yeast Saccharomyces cerevisiae use chemical signaling to identify cells of opposite mating type and to initiate the mating process. First cells of mating type A release a-factor, which binds to receptors on nearby cells of mating type B. Meanwhile, B cells release b-factor, which binds to specific receptors on A cells. Both these "factors" are small proteins of about 20 amino acid in length. Binding of these factors to the receptors induces changes in the cells that lead to their fusion, or mating. The resulting A/B cell combines in its nucleus all the genes from both A and B cells, (diploid).

As humans communicate with each other, and so do other animals, it is definitely undoubtful that cell as well need to communicate among themselves. As mentioned above, there are several different ways of how the cells communicate.

All communication involving cells can be explained in terms of a force of attraction (called affinity) between molecules. Components that allow detection are called receptors and they often have a cavity shape which allows other molecules to lock into them. The receptor ahs an affinity for a particular message or signal.

Generally, we can think of chemical signals as being stimulatory-or inhibitory- for controlling levels of activity. However, the situation is seldom the simple as there are hundreds of different types of signals and they all work in concerted coordination to carefully regulate what happens in a cell according to a wide range of influencing factors. Cell processes are not so much on or off, but, held in a dynamic state of tension. Many different protein messages or components may determine the state of a cell (for example, the cell responsible for secreting a pituitary hormone - prolactin - has been shown to respond to at least twenty different signals).

Signal transduction pathway: a series of steps linking a mechanical or chemical stimulus to a specific cellular response.

Amplification: the strengthening of stimulus energy during transduction.

Apoptosis: a program of controlled cell suicide, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die.

Gap junction: a type of intercellular junction in animals that allows the passage of materials between cells.

Growth factor: a protein that must be present in the extracellular environment (culture medium or animal body) for the growth and normal development of certain types of cells.

Ligand: a molecule that binds specifically to another molecule, usually a larger one.

Yeast: Single-celled fungus that reproduces asexually by binary fission or by the pinching of small buds off a parent cell; some species exhibit cell fusion between different mating types.

Protein kinase: an enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein.

Local regulator: a secreted molecule that influences cells near where it is secreted.

Glycogen: an extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.

http://www.youtube.com/watch?v=tMMrTRnFdI4&feature=related