| Hydrogen compound | 17 |
| Derivative of ammonia | 21 |
| An ammonia derivative | 21 |
| Alkaline compound | 17 |
| '..., excavating for --' | 32 |
| Chemical compounds | 18 |
| Some organic compounds | 22 |
| Nitrogen compounds | 18 |
| Ammonia derivatives | 19 |
| Ammonia compounds | 17 |
| Organic compounds with nitrogen | 31 |
| Certain nitrogen compounds | 26 |
| Compounds with nitrogen | 23 |
| Acid type | 9 |
| ___ acids | 9 |
| Acid | 4 |
| Kind of alcohol | 15 |
| Acid in proteins | 16 |
| Protein-building acid | 21 |
| __ acid | 7 |
| Protein acid | 12 |
| Essential acid | 14 |
| PABA part | 9 |
| Acid in protein | 15 |
| ___ acid (protein component) | 28 |
| Kind of acid in protein | 23 |
| Essential ___ acids | 19 |
| Kind of acid in proteins | 24 |
| Protein building block, for short | 33 |
| Certain acid | 12 |
| An acid | 7 |
| Acid head? | 10 |
| ____ acid | 9 |
| __ acid (protein component) | 27 |
| Protein acid, for short | 23 |
| Part of PABA | 12 |
| Kind of resin | 13 |
| Kind of protein-building acid | 29 |
| Kind of acids | 13 |
| Kind of acid found in protein | 29 |
| -- acid | 7 |
| _____ acid | 10 |
| Sort of acid in proteins | 24 |
| Sort of acid in protein | 23 |
| Protein building block | 22 |
| Organic acid form | 17 |
| Kind of group, in chemistry | 27 |
| Kind of acid or resin | 21 |
| Essential type of acid | 22 |
| Building block, informally | 26 |
| Another type of acid | 20 |
| -- acids | 8 |
| ___ acids (main components of proteins) | 39 |
| ___ acid (protein builder) | 26 |
| __ acid (protein part) | 22 |
| Type of acid found in proteins | 30 |
| Relating to NH2 | 15 |
| Protein-related acid | 20 |
| Protein acid, informally | 24 |
| Popular puzzle acid | 19 |
| Part of a chemistry group | 25 |
| Nonessential -- acids | 21 |
| Nitrogen/hydrogen radical | 25 |
| Monomer of proteins, informally | 31 |
| Metabolic acid | 14 |
| Like an acid that builds proteins | 33 |
| Kind of plastic or resin | 24 |
| Kind of acids in proteins | 25 |
| Kind of acid synthesized to produce aspartame | 45 |
| Essential acid, familiarly | 26 |
| Essential acid type | 19 |
| Essential ___ acid | 18 |
| Essential __ acids | 18 |
| Containing the group NH2 | 24 |
| Common acid | 11 |
| Certain building block, informally | 34 |
| Another kind of acid | 20 |
| Alpha-___ acid | 14 |
| Acid of dietary importance | 26 |
| Acid in proteins, informally | 28 |
| Acid group | 10 |
| Acid class | 10 |
| ___ acid (protein building block) | 33 |
| ___ acid (building block of biology) | 36 |
| __ resin (organic adhesive) | 27 |
| __ acids (protein building block) | 33 |
| __ acid (protein building block) | 32 |
| Body builder? | 13 |
| Protein builder | 15 |
| It may be essential | 19 |
| Tryptophan, for one | 19 |
| Protein component | 17 |
| Metabolism molecule | 19 |
| Lysine or tryptophan | 20 |
| Lysine or leucine | 17 |
| It might be essential | 21 |
| Important factor in growth | 26 |
| Key with no sharps or flats | 27 |
| Key of Mendelssohn's Symphony No. 3 | 39 |
| Key with all white notes | 24 |