Amino Acids and Essential Nutrition

Amino Acids

• Nutritionally essential amino acids are those that cannot be synthesized by the body and must be obtained through the diet.
• Examples of essential amino acids: Val, Leu, Ile, Phe, Met, Thr, Lys, Arg, His, Trp
• Semiessential amino acids require nutritionally essential amino acids for their synthesis.

Non-Essential Amino Acids

• Non-essential amino acids can be synthesized by the body and are not required in the diet.
• Examples of non-essential amino acids: Gly, Ala, Ser, Pro, Cys, Tyr, Asn, Gln, Asp, Glu

Structure of Amino Acids

• Amino acids have a carboxyl group, a primary amino group, and a distinctive side chain (R-group) bonded to the α-carbon atom.
• At physiologic pH, the carboxyl group is dissociated, forming the negatively charged carboxylate ion (–COO–), and the amino group is protonated (–NH3+).
• In proteins, the carboxyl and amino groups are combined through peptide linkage and are not available for chemical reaction except for hydrogen bond formation.

The Genetic Code

• The genetic code specifies 20 L-α-amino acids encoded by nucleotide triplets called codons.
• Some proteins contain additional amino acids that arise by post-translational modification of an amino acid already present in a peptide.

Selenocysteine

• Selenocysteine is the 21st protein L-α-amino acid, found in proteins from every domain of life.
• Selenocysteine is not the product of a post-translational modification, but is inserted directly into a growing polypeptide during translation.
• Selenocysteine is specified by a large and complex genetic element that utilizes the UGA anticodon that normally signals STOP.

Proline

• Proline differs from other amino acids in that its side chain and α-amino N form a rigid, five-membered ring structure.
• Proline has a secondary (rather than a primary) amino group and is often referred to as an imino acid.
• The unique geometry of proline contributes to the formation of the fibrous structure of collagen and often interrupts the α-helices found in globular proteins.

Sickle Cell Disease

• Sickle cell disease is an inherited blood disorder marked by defective hemoglobin.
• It inhibits the ability of hemoglobin in red blood cells to carry oxygen.
• The disease results from the substitution of polar glutamate by nonpolar valine at the sixth position in the β subunit of hemoglobin.

Buffers

• A buffer is a solution that resists changes in pH when small amounts of acid or base are added to it.
• Buffers are typically composed of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal amounts.
• Buffers are crucial in various biological, chemical, and laboratory applications where maintaining a stable pH is essential.

Titration

• Amino acid titration refers to the process of determining the concentration of amino acids in a solution by gradually adding a titrant solution of known concentration until a specific endpoint is reached.
• During the titration, the pH of the amino acid solution is monitored, and changes in pH occur as the titrant is added.
• At the endpoint, the pH reaches a certain value, indicating that the stoichiometric equivalence point has been reached.