Cyclic AMP

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.

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:

1. The hormone binds to the receptor.

2. Hormone-bound receptor binds to G-protein and replaces GDP (inactive state) with GTP (active state).

3. Active G-proteins react with adenylate cyclase.

4. 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.

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).

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.