Amino Acids

Written By Sanjay Adireddi

Amino acids serve as the building blocks of proteins. Each amino acid has a central carbon atom (called the alpha carbon) to which four groups are attached. Amino acids are the monomers of polypeptides, which are formed through dehydration reactions between amino acids.

1. Amino Group (-NH₂): This consists of a nitrogen atom bonded to two hydrogen atoms.

2. Carboxyl Group (-COOH): This contains a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group.

3. Side Chain (R Group): This is a variable group that determines the identity and properties of the amino acid. There are 20 different amino acids commonly found in proteins, each with a unique side chain.

Role in the Human Body

Amino acids play an important role in the human body. Amino acids can be categorized into essential and non-essential based on the body's ability to synthesize them. Essential amino acids are those that the body cannot produce on its own and must be obtained from the diet.

  • Protein Synthesis: Essential amino acids are necessary for the synthesis of proteins, which are vital for growth, repair, and maintenance of body tissues.

  • Enzyme Production: They are critical for the formation of enzymes that catalyze biochemical reactions in the body.

  • Hormone Regulation: Essential amino acids contribute to the synthesis of hormones that regulate various physiological processes.

  • Immune Function: They are vital for the production of antibodies and other immune system components.

  • Neurotransmitter Production: Essential amino acids serve as precursors for neurotransmitters that affect mood, cognition, and overall brain function.

  • Metabolism: They play key roles in metabolic pathways, including energy production and nutrient metabolism.

Since the body cannot synthesize essential amino acids, it is crucial to obtain them from dietary sources. A balanced diet that includes a variety of protein-rich foods, such as meat, fish, poultry, eggs, dairy products, legumes, nuts, and seeds, ensures adequate intake of essential amino acids.

Memorization of Amino Acids

While memorizing the structure of the 20 standard amino acids can seem like a daunting task, with the aid of various mnemonics, it does not have to be as difficult as it is often painted out to be. They differ primarily in the structure of their side chains (R groups). These side chains confer unique chemical properties to each amino acid, influencing their role in protein structure and function.

1. Nonpolar (Hydrophobic) Side Chains

  • Glycine (Gly, G): Simplest amino acid, with a hydrogen atom as its side chain

  • Alanine (Ala, A): Methyl group

  • Valine (Val, V): Branched side chain

  • Leucine (Leu, L): Branched side chain similar to valine, but with an additional CH₂ group

  • Isoleucine (Ile, I): Branched side chain isomeric with leucine

  • Proline (Pro, P): Cyclic side chain that bonds back to the amino group, forming a ring

  • Methionine (Met, M): Contains sulfur

Remember the nonpolar amino acids through GAVLIP. Think of GAVLIP is like a growing plant. Glycine is a short plant without a noticeable stem, alanine adds length to the stem, valine is where the plant bifurcates (it looks like a valine). The stem continues to extend in leucine and isoleucine. In proline, the plant folds back in on itself, forming a ring-like structure. To remember the other amino acids in this group use the saying “methphetyrp.”

2. Polar, Uncharged Side Chains

  • Serine (Ser, S): Hydroxymethyl group

  • Threonine (Thr, T): Hydroxyl group and an additional methyl group

  • Cysteine (Cys, C): Contains a thiol group

  • Tyrosine (Tyr, Y): Similar to phenylalanine but with a hydroxyl group attached to the benzene ring

  • Asparagine (Asn, N): Amide group

  • Glutamine (Gln, Q): Similar to asparagine but with an additional CH₂ group

Remember the polar, uncharged amino acids through STCTAG.

3. Polar, Positively Charged (Basic) Side Chains

  • Lysine (Lys, K): Long side chain ending with an amino group

  • Arginine (Arg, R): Contains a guanidinium group

  • Histidine (His, H): Contains an imidazole ring

4. Polar, Negatively Charged (Acidic) Side Chains

  • Aspartate (Asp, D): Carboxyl group

  • Glutamate (Glu, E): Similar to aspartate but with an additional CH₂ group

Remember the polar, charged amino acids through AGLAH.



Author: Sanjay Adireddi

Reference Article: https://www.ncbi.nlm.nih.gov/books/NBK557845/

Sanjay Adireddi
Previous

Next-Gen Sequencing
Next

Hamilton’s Rule