Adenosine is composed of an acid and a sugar.

From the mitochondria

This is correct.

Adenosine is an "autocoid" inhibitory neurotransmitter that generally protects the nervous system and other organs from being overstimulated or incurring damage due to other processes.

Substances such as caffeine (a xanthine stimulant) block adenosine receptors to result in increases of dopamine and glutamate (excitatory neurotransmitters).

In this way, adenosine's job in the CNS is to prevent overstimulation.

In the lungs, adenosine acts to decrease cAMP (cyclic-adenosine monophosphate) levels to induce bronchospasm.

In the heart, it acts on the AV (atrioventricular node) to induce transient heart block, and has a regulatory role in maintaining heart rhythm.

Adenosine is a combination of the molecule adenine and the sugar ribose. It is a nucleoside that plays a key role in various biochemical processes in the body, such as energy transfer and signaling pathways.

By phosphorylation