Question

As discussed in your text book, there are four categories of chemical signalling found in multicellular organisms; paracrine signalling, endocrine signalling, autocrine signalling and direct signalling across gap junctions. For this written assignment you will choose one of these signalling pathways to investigate in more detail.

• Choose one out of paracrine signalling, endocrine signalling, autocrine signalling and direct signalling and describe briefly the process by which this occurs.

• Pick a representative signal molecule from the pathway you have chosen and indicate its function, the type of cell in which it is made and the specific manner in which it acts as a signalling molecule, including the receptor that it binds to.

For example if you chose the endocrine signalling pathway you could consider looking at a hormone such as insulin. You would describe the cells from which insulin is secreted and state the overall role of insulin in the body. In signalling pathways, each signal molecule has a receptor that it binds to, so you would indicate what the receptor for insulin is called and what immediate outcome the binding of insulin has to that receptor i.e. in the case of insulin, which regulates glucose uptake in the body, does the receptor directly interact with glucose or is it just part of a much larger signalling cascade.

To give you an indication of the complexity of cell signalling, visit the KEGG (Kyoto Encyclopaedia of Genes and Genomes) PATHWAY database. This database maps biological pathways and displays them as a collection of diagrams or graphs. If you wish to read more about it visit the overview page of the database here:   http://www.genome.jp/kegg/kegg1a.html  

• Open the KEGG PATHWAY Database homepage http://www.genome.jp/kegg/pathway.html

On this page, you can browse various types of pathways, including metabolic and signalling pathways or you can search for terms and find the associated pathways.

• Using the search box, search for the molecule you have discussed above by entering its name.
• KEGG may give you the choice between several pathways, choose one of these and click on the link under the heading ‘entry’. (this will read something like map01578)
• Read the description of the pathway and write down its name then click on the image of the map.
• If possible copy the image of the map and insert it into your written assignment, if this does not work for you provide a URL so that the page can easily be accessed.

The map consists of a set of rectangles and circles which represent molecules, connected by lines which indicate how these molecules interact or relate with each other. To understand how the information is organised on the map, click on the "Help" button at the top left of the screen. You can explore the map by clicking on its individual elements and investigate the kinds of information is available.

• Try to identify your chosen molecule on the map and make a note of the number and names of other molecules it directly interacts with in this pathway. If you are unable to identify your molecule of choice see if you can find its receptor, which you identified earlier in this assignment.
• Click on the shape that contains your molecule of interest (or its receptor) (this will redirect you to a page that lists the signalling pathways in which that molecule is involved and any diseases associated with it)
• Take a note of the names of at least three other pathways indicated on this page and comment on whether your molecule is linked with any diseases. (If there is no disease association there will be no entry in the table)

Remember to include APA formatted citations for

Answer 1

1. Endocrine signaling :- insulin is secreted from beta cells (type of isket cells) of pancreas.

• Role of insulin is to regulate amount of glucose in blood stream i.e it reduces blood glucose levels (hypoglycemic effect) .
• Insulin receptor IGF I and IGF II (tyrosine kinase comprising 2alpha and 2 beta subunits ) present on surface of liver , muscle and fat.
• Insulin releases from cell and bind to extracellular part of receptor ,shape changes and communicate to intracellular parts cause it to bind ATP and phosphorylate proteins and singal cascade occur and causes glucose receptors to binds to membrane surface that provides channel for glucose entry into cells and converted into glycogen and in this way insulin woks in so that glucose is taken up by cell and blood glucose reduces.