cell_communication


 * __Chapter 11 - Cell Communication__

Communication Between Mating Yeast Cells**

Yeast cells (Saccharomyces Cerevisiae) use chemical signaling to identify opposite mating cells and initiate the mating process. These two opposite mating cells are analagous to females and males. These two sexes, or mating types, are called "a" and a. Cells of the "a" sex secrete a chemical signal called "a"-factor, which binds to receptor proteins on the nearby a cells. Cells of the a cells secrete a chemical signal called a-factor, which binds to receptor proteins on "a" cells. Without entering the cells, these chemical signals cause the cells to grow towards each other and the result is the fusion, or mating, of two cells. The new a/a cell contains genes from both original cells.


 * [[image:http://fig.cox.miami.edu/~cmallery/150/memb/c11x1yeast-signaling.jpg]]

Local and Distant Cell Communication in Animals**

There are two main kinds of local cell signaling in animals. Hormonal Signaling targets cells at greater distances.

- Paracrine Signaling: a secreting cell acts on nearby target cells by discharging molecules of a local regulator in the extracellular fluid. - Synaptic Signaling: a nerve cell releases neurotransmitter molecules into a synapse, the narrow space between the target cell and the transmitting cell. - Hormonal Signaling: Hormones signal target cells at much greater distances. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells, but only specific target cells will recognize and respond to a given chemical signal.


 * [[image:local_and_distant_communication.jpg]]

The Three Stages of Cell Signaling: Reception, Transduction, and Response. [|[Cell Signaling with Visual]]

-** __Reception__ is the target cell's detection of a signal coming from outside the cell. A chemical signal is "detected" when it binds to a cellular protein, usually at the cell's surface. - With the binding of a signal molecule, there is a change in the receptor protein. This initiates the process of transduction. This stage of __transduction__ converts the cell signal to a form that will create a specific response from the cell. Most of the time transduction requires a sequence of changes in a series of different molecules (a signal transduction pathway), but sometimes it can occur in a single step. - __Response__ is the final step in this three step process of cell signaling. A specific cellular response is a result of the transduced signal. This response may be any cellular activity one can think such as the rearrangement of the cytoskeleton, or the activation of specific genes in the nucleus.


 * What is a ligand? How does a ligand assist in transduction?**

A __ligand__ is a small molecule that binds to a larger one. Ligand binding causes the receptor protein to undergo a change in shape which results in the direct activation of the receptor so it can interact with another molecule.


 * The difference between G-Protein-Linked Receptors & Tyrosine-Kinase Receptors [Visuals in the Book - Pages 193 &194]**

__G-Protein-Linked Receptors__ (pg 193): - A G-Protein-Linked Receptor is a membrane protein that works in conjunction with a G protein and another protein, usually an enzyme. Without the extracellular signal molecule specifically related to the receptor, all the proteins stay inactive. The inactive G protein has a GDP molecule bound to it. - When the signal molecule binds to the receptor, the ligand bond causes the receptor to change shape in a way that it activates the G protein. The molecule GTP then replaces the molecule of GDP on the G protein. This G protein then binds to and activates the enzyme which carries out the cellular response. - The G protein will eventually catalyze the hydrolysis of its GTP and dissociate itself from the enzyme, making itself available for reuse. - Helps with normal embryological development.



__Tyrosine-Kinase Receptors__ (pg 194):

- If there is an absence of specific molecules, tyrosine-kinase receptors exist as single polypeptides in the plasma membrane. A single transmembrane a helix connects the extracellular portion of the protein to the protein's cytoplasmic portion. This part of the protein is responsible for the receptor's tyrosine-kinase activity and also has a series of tyrosine amino acids. - When signal molecules bind to the binding sites, these polypeptides come together forming a dimer. - The ADP converts to ATP activating the tryosine-kinase receptor or the phosphorylated dimer. This activates the proteins which carry out the cellular response. Tyrosine-Kinase receptors often activate many signal transduction pathways at once. This helps in regulating complicated functions such as cell reproduction or cell division. Without the appropriate activation of these receptors, uncontrolled cell growth can occur such as cancer.


 * Important Words To Know in Chapter 11 - Cell Communication:**
 * Signal Transduction Pathway - pg. 189
 * Local Regulator - pg. 189
 * Hormones - pg. 190
 * Ligand - pg. 192
 * G-Protein-Linked Receptors - pg. 192
 * G Protein - pg. 192
 * Tyrosine Kinase - pg.193
 * Tyrosine-Kinase-Receptors - pg. 193
 * Ligand Gated Ion Channels - pg. 194
 * Protein Kinase - pg. 195
 * Protein Phosphates - pg. 196


 * Related Assignments:**
 * "Cell Signal" Simulation
 * Outline: Chapter 11 - Cell Communication (obj. 2, 3, & 5)