AMINO ACIDS M.F.Ullah, Ph.D ShowketH.Bhat, PhD • COURSE TITLE: BIOCHEMISTRY 1 COURSE CODE: BCHT 201 PLACEMENT/YEAR/LEVEL: 2nd Year/Level 4, 1st Semester
PROTEINS Proteins are polymer (chain) made up of smaller units called amino acid which are linked together by peptide bonds Amino acids Protein
Basic Functions of Proteins • Contain carbon, hydrogen, oxygen, nitrogen, and/or sulfur • Serve as structural components of animals (muscle proteins-actin & myosin/ eye lens protein-crystallins) • Serve as control molecules (enzymes) in biochemical reactions • Serve as transport (hemoglobin) and messenger molecules (hormones)
Amino Acid • Consist of a central carbon atom bonded to: a hydrogen, a carboxylic acid group, an amino group, and an additional side group “R” that is unique to each amino acid • The side group “R” for each amino acid is different as a result amino acid differ in: shape, size, composition, electrical charge, and pH.
Classification of amino acids There are three types of classification system for amino acids: Classification based on protein constituent 2. Classification based on the structure of amino acids (“R” group/side chain) 3. Classification based on dietary requirement
1. On the basis of protein constituents, amino acids are classified as “proteinogenic” and “ non-proteinogenic” amino acids Proteinogenic amino acids are those which serve as the building blocks of proteins i.e. proteins are made up of proteinogenic amino acids. There are 20 proteinogenic amino acids in eukaryotes and these are called standard amino acids. These are given below:
Non- proteinogenicamino acids are those amino acids which are not the part of proteins but serve other independent functions. Example: Ornithine & citrulline are non-protenogenic amino acids which are involved in the synthesis of urea. 2. Based on the structure of amino acids (“R” group/side chain), amino acids can be polar or non-polar Side chain “R” group in polar amino acids have charged groups such as amino group (+ve charge) , carboxylic acid group (-ve charge) or polar groups such as Hydroxyl group. Side chain “R” group in non-polar amino acids have non-polar groups like methylene side chain or benzene rings. Note: There are two standard amino acids in which acid chain “R” group contain sulphur (S). These sulphur containing amino acids are cysteine and methionine.
3. Classification based on the dietary requirements Essential Amino Acids Essential Amino acids : Nutritionally must be present in diet because these can not be synthesized in our body; The body lacks enzymes that can synthesize these amino acids from any precursor molecules. • 10 amino acids not synthesized by the body • arg, his, ile, leu, lys, met, phe, thr, trp, val (arg is considered semi-essential:Body can synthesize this amino acid but not in adequate amounts to support proper growth ) • Must be obtained from the diet • All in diary products • Their deficiency affects growth, health and protein synthesis.
Non-Essential Amino Acids • Non-Essential Amino acids : Need not be present in diet because the body can take care of their synthesis when required or when these are deficient in the diet. These are the rest of amino acids that are formed in the body in amount enough for adults and children. They are the remaining 10 amino acids.