Animated Solution for Chemistry - Biomolecules: Which of the following is not an essential amino acid?

Amino acids are the fundamental building blocks of proteins, and they play a crucial role in almost all biological processes. When we talk about human nutrition, we classify these amino acids into two broad categories based on a very simple criterion: can our body make them from scratch?

If our body has the metabolic pathways to synthesize an amino acid, we call it a non-essential amino acid. The term "non-essential" doesn't mean we don't need them; it simply means it's not essential to get them directly from our food because our body can manufacture them on demand.

Conversely, if our body lacks the machinery to build a specific amino acid, it becomes an essential amino acid. These are absolutely critical to include in our daily diet. Without them, our body cannot synthesize the necessary proteins, leading to severe health issues.

To tackle questions like this, you must memorize the list of the 10 essential amino acids. A common mnemonic to remember them is "PVT TIM HALL" (Private Tim Hall):

Phenylalanine Valine Threonine Tryptophan Isoleucine Methionine Histidine Arginine Leucine Lysine

Now, let's look at the options provided in the question:

(a) Leucine: Present in our list (the 'L' in HALL). It is essential. (b) Valine: Present in our list (the 'V' in PVT). It is essential. (c) Lysine: Present in our list (the other 'L' in HALL). It is essential. (d) Tyrosine: This is not on our list.

Tyrosine is actually synthesized in the body from another amino acid, phenylalanine. Because our body can produce it (as long as we have enough phenylalanine), Tyrosine is classified as a non-essential amino acid.

Therefore, the correct answer is Tyrosine.