The inability of an organism to produce certain
proteins can occur when an organism is lacking
an enzyme needed to combine
(1) oxygen molecules (3) amino acids
(2) simple sugars (4) biological catalysts

The answer is option  (3).

Amino acids are joined together to form proteins.

 Living organisms have enzymes which are capable of linking amino acids together by creating a peptide bond between the amino acids. This process takes place in the A and P site of ribosomes in the cell during translation.

One such enzyme is called peptidyl transferase. If an organism lacks such an enzyme,  synthesis of the proteins catalyzed by that particular enzyme in its cells will not take place. If amino acids cannot be joined together, then a polypeptide chain, which forms the primary structure of the protein will not be formed.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.