Chapter 13, pages 443-449

Acetylcholine receptor.

The nicotinic Acetylcholine receptor was discussed in class.  For more information about the subunits and the conformational change that occurs, go back to page 426-428.

Voltage-gated and ligand-gated channels.

For the voltage gated channels in neurons, Ca⁺² enters the cell and acts as a "second messenger" that triggers the fusion of acetylcholine containing vesicles with the membrane.  This releases acetylcholine into the synaptic cleft.   Note: usually "second messenger" is used to refer to chemicals that are inside the cell, these "second messengers" relay the signal that a molecule on the outside of the cell sends.  In this case, Ca⁺² was outside the cell, but it is relaying the "message of the polarized membrane. 

• How does the voltage-gated Ca⁺² channel and the acetylcholine-gated channel work to send a neuronal signal?
• How are cation channels specific for cations?  How are anion channels specific for anions?

Receptor Enzymes

The insulin receptor is a tyrosine kinase.   Be able to describe how the binding of insulin activates a target protein (figure 13-6).  Figure 13-7 shows how insulin activates a cascade of protein activation.  It is not necessary to memorize this cascade, but do walk yourself through it. 

• What  are the advantages of a catalyst activating a catalyst? (One advantage is given in the text, can you come up with another?)

Figure 13-8 shows how insulin triggers the activation of glycogen synthase via   phosphorylation of IRS-1.  You should be able to describe this pathway, and its relationship with the GluT4 receptor (Box 12-2). 

• What are two other enzyme receptors that are similar to the insulin receptor?

Guanyl cyclase generates cGMP.  You should be able to draw the structure for this.

• What are the effects of cGMP in the kidney?  intestine? cardiac smooth muscle? brain?
• What is guanyl cyclase activated by in the kidney?  What is the net effect of this activation?  What happens to vascular smooth muscle when this samw hormone binds to the guanyl cyclase receptor?
• How do some gram negative bacteria cause diarhea?
• How do nitrogycerin tablets bring about relief from angina?