You might already know about ATP being a form of energy within the body, but do you know how it is able to create cyclic adenosine monophosphate (AMP)? Cyclic AMP is a second messenger found in many organisms that is able to aid in signal transduction between cells.
Cyclic AMP is found in eukaryotic and prokaryotic organisms! Eukaryotic organisms are organisms that contain a nucleus and membrane-bound organelles. Examples of eukaryotic organisms are animals, plants, protists, and fungi. Prokaryotic organisms do not contain a nucleus or membrane-bound organelles. An example of a prokaryote is bacteria.
Second messengers are molecules released by cells in response to first messengers, which are extracellular signaling molecules. There are three types of second messengers which are cyclic nucleotides (cAMP and cGMP), inositol triphosphate (IP3) and diacylglycerol (DAG), and calcium ions (Ca2+).
What is the definition of cyclic AMP?
The definition of cyclic AMP is a molecule made from ATP using the enzyme adenylyl cyclase. This transformation can show you that two of the phosphates are removed from the ATP molecule, with the leftover phosphate being linked to the ring-shaped sugar.
Figure 1. Cyclic AMP transformation diagram. Source: OpenStax College Biology
What is the function of cyclic AMP?
The function of cyclic AMP helps with the regulation of glycogen, sugar, and lipid metabolisms. Once ATP transforms into cyclic AMP, it is able to activate the protein kinase A enzyme. This activation of the PKA enzyme allows cellular response to occur.
Protein kinase A is an enzyme that is found in different types of cells and has a different target protein depending on which type of cell it is found in. It is also known as cAMP-dependent protein kinase.
What activates cyclic AMP?
In order to synthesize cyclic AMP, the adenylate cyclase must be activated. Adenylate cyclase is activated using stimulatory G-protein, a type of regulatory protein that is known as guanylate nucleotide binding protein. There is a cycle for G-proteins that allow them to create more or less of cyclic AMP:
The hormone binds to the receptor.
Hormone-bound receptor binds to G-protein and replaces GDP (inactive state) with GTP (active state).
Active G-proteins react with adenylate cyclase.
G-protein returns to GDP state via hydrolysis and makes it inactive.
What deactivates cyclic AMP?
Cyclic AMP is deactivated by a type of enzyme known as phosphodiesterase. They deactivate the cyclic AMP by breaking the ring found in the cyclic AMP's structure. When the ring in cyclic AMP is broken, it turns into AMP.
What is the structure of cyclic AMP?
Cyclic AMP has the chemical formula of C10H12N5O6P, and its structure can be seen in Figure 2 below.
Figure 2. Cyclic AMP chemical structure. Source: wikipedia.org
Cyclic AMP pathway
The cyclic AMP pathway shows the creation of cellular response starting all the way from the beginning of adenylyl cyclase transforming ATP into cyclic AMP. This cyclic AMP is able to activate protein kinase A and allows cellular response to occur.
Cyclic AMP in the lac operon
The lac operon is a group of genes with one promoter that encode proteins to use lactose as an energy source for enteric bacteria. Enteric bacteria are bacteria found in the intestines.
Remember that bacteria prefer to use glucose as their fuel of choice, so in order for the lac operon to turn on, there needs to be no glucose for them available.
Cyclic AMP is also found in the lac operon, where it regulates the catabolite activator protein (CAP). RNA polymerase, an enzyme found in the lac operon that aids in transcription, does not bind as well to the promoter as expected, so it needs CAP to assist by binding to a region of DNA next to the promoter. The CAP bound next to the promoter will help the RNA polymerase bind to the promoter. The gene for CAP is found in the bacterial chromosome, and it is not located near the lac operon, but it is constantly "on" so CAP is always able to monitor glucose levels. CAP is not always able to bind to DNA and is instead regulated by cyclic AMP (cAMP).
E. coli uses cAMP as a signal when glucose levels are low, and cAMP is able to change the shape of CAP in order to allow it to bind to DNA.
Remember, cAMP levels depend on the amount of glucose that can be transported into the cell. If there are high levels of glucose, then there are low levels of cAMP. If there are low levels of glucose, then there are high levels of cAMP.
Similarities and differences between cyclic AMP and AMP
There are a few similarities between cyclic AMP and AMP:
They are both nucleotides.
They are both derived from ATP.
They have a similar structure with a ribose sugar, an adenine base, and a phosphate group.
There are a few differences between cyclic AMP and AMP:
Cyclic AMP has a cyclic shape, while AMP does not.
Cyclic AMP is a secondary messenger, and AMP is a nucleotide that converts into ADP and ATP.
Cyclic AMP - Key takeaways
- Cyclic AMP is a molecule made from ATP using the enzyme adenylyl cyclase.
- Cyclic AMP helps with the regulation of glycogen, sugar, and lipid metabolisms.
- Cyclic AMP is activated using adenylate cyclase. Cyclic AMP is deactivated using phosphodiesterase.
- Cyclic AMP activates protein kinase A and allows it to produce a cellular response.
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