Question 15 of 25 Adenosine triphosphate (ATP) is the main energy currency used in cells. ATP hydrolysis is coupled with unfavorable reactions, making the net change in energy for the set of reactions less than 0, which is favorable. Although ATP is the main energy currency, other molecules can fulfill this role and take part in coupled reactions. Determine whether each of the phrases or examples describes a thioester, reduced cofactor, or phosphorylated compound.

Thioesters- the Sulfur-Carbon bond is hydrolyzed, e.g. AcetylCoA

Reduced cofactor- These compounds accept electrons during the oxidation of substrates and energy is released when they are oxidized, e.g. Ubiquinol

Phosphorylated compounds- These compounds yield H₂P0₄⁻ upon hydrolysis, e.g. Phosphocreatine.

Explanation: Thioesters are esters in which the linking oxygen atom is replaced by a sulphur atom. They are the product of esterification between a carboxylic acid and a sulfhydryl group (thiol). They have the functional group R–S–CO–R'. Thioesters are common intermediates in many biosynthetic reactions. Examples include malonyl-CoA, acetyl-CoA, and propionyl-CoA. In the hydrolysis of thioesters, the sulfur-carbon bond is hydrolyzed.

Cofactors can be either organic or inorganic molecules that are required by enzymes to function. Cofactors can be oxidized or reduced for the enzymes to catalyze the reactions.  Examples include, NAD, FAD, NADP, Coenzyme Q₁₀. Coenzyme Q₁₀ exists in three redox states, fully oxidized, partially reduced, and fully reduced. Ubiquinol is the reduced (electron-rich) form of coenzyme Q₁₀. Coenzyme Q₁₀ is vital for proper transfer of electrons within the mitochondrial oxidative respiratory chain, whose main function is to produce adenosine triphosphate (ATP). These compounds accept electrons during the oxidation of substrates and energy is released when they are oxidized.

Phosphorylated compounds are compounds with a phosphoryl group (PO₃²⁻) attached to its molecules. These compounds yield an inorganic phosphate (H₂P0₄⁻) upon hydrolysis. Phosphorylation is especially important for protein function as this modification activates or deactivates almost half of the enzymes, thereby regulating their function. Examples include, glucose-1-phosphate, phosphoserine, phosphocreatine, etc.