The nitrogenous waste product that is a small, water-soluble molecule produced from protein breakdown in the liver is .

The nitrogenous waste product that is a small, water-soluble molecule produced from protein breakdown in the liver is urea.

Here are the steps of how it is produced:

1. Protein Breakdown: The process begins with the breakdown of proteins in the liver. These proteins are broken down into their constituent amino acids.

2. Deamination: The amino acids undergo a process called deamination. This process removes the amino group from the amino acid. The amino group contains nitrogen.

3. Formation of Ammonia: The removal of the amino group results in the formation of ammonia (NH3). Ammonia is toxic to the body and needs to be converted into a less harmful substance.

4. Conversion to Urea: The liver cells convert the ammonia into urea through a series of reactions known as the urea cycle. Urea is less toxic than ammonia and is soluble in water.

5. Excretion: The urea is then transported to the kidneys where it is excreted from the body in the urine.