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Secondary Messenger System: Adenylyl Cyclase Mechanism

Secondary Messenger System: Adenylyl Cyclase Mechanism

Author: Aaron Mullally

- know which class of hormones utilize this type of messenger system

- know what the various membrane and intracellular components of the system are

- know how this system is activated and inactivated

This packet covers a specific secondary messenger system called the adenylyl cyclase mechanism.

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Secondary messenger systems are used by chemical messenges that are unable to cross plasma membranes and interact with the inside of cells. The types of chemical messages that utilize these systems are the polar messengers (peptides, proteins, amines {except thyroid hormone}). Secondary messenger systems have these few basic components:

  • G proteins - G = guanosine triposphate (GTP) binding proteins. G proteins are attached to a portion of receptors. When activated subunits of G proteins are detached and either activate or deactivate mechanisms within the cell
  • α β γ subunits - these are the units that the G proteins are made of. The alpha and beta subunits are the structural parts of the G protein while the alpha subunit is the active portion. When a G protein is activated the alpha subunit detaches it travels within the cell and can either activate or inhibit certain actions.

The adenylyl cyclase system works in the following steps:

  1. a hormone or neurotransmitter binds to a surface receptor which creates a conformational (shape) change with the receptor itself
  2. the conformational changes causes the α subunit of the G protein to detach (disassociate)
  3. the α subunit interacts with another membrane protein/enzyme called adenylyl cyclase; this activates the adenylyl cyclase enzyme
  4. adenylyl cyclase converts adenosine triphosphate (ATP) into cAMP
  5. cAMP binds with a specific protein that is called a kinase (cAMP dependent kinase)
  6. This activates a cascade of enzymatic pathways leading to the cellular response to the hormone
  7. ATP will continue to be converted into cAMP as long as the hormone and recepter remain bound. When the hormone is detached from its receptor this system goes in reverse and shuts down
  8. Since cAMP is directly activating the cellular responses it is considered the secondary messenger

This is the most widely used secondary messenger system by the endocrine system and is utilized by peptides and proteins. *Chemical messages that utilize this system are: ACTH, LH, FSH, TSH, ADH, HCG, MSH, CRH, beta 1 and beta 2 receptors, calictonin, PTH, glucagon

* Costanzo, Linda. Board Review Series: Physiology, 2nd Edition. Baltimore, Lippincott Williams & Wilkins, 1998. Print

Here is a useful link to show you this step by step as well:

Source: Mind of Aaron

Adenylyl Cyclase Mechanism

This video gives an overview of this particular secondary messenger system

Source: Self made