Quiz 5: Amino Acids and Proteins


The amino acids are the building blocks of proteins. These can be classified by different ways as follows: On the basis of polarity: 1. Polar amino acids: like glutamate, arginine, lysine, tyrosine, cysteine etc 2. Non-polar amino acids: like glycine, leucine, valine, phenylalanine, proline, methionine etc. On the basis of acid-base properties: 1. Acidic amino acids: like aspartate, glutamate 2. Basic amino acids: like arginine, histidine etc 3. Neutral amino acids: like tyrosine, asparagines, threonine, serine etc. On the bases of -R group or side chain: 1. Alkyl chain: like alanine, glycine 2. Aromatic chain: like phenylalanine, tryptophan, tyrosine etc. 3. Branched chain: like valine, leucine, isoleucine On the basis of functional group: 1. Hydroxyl group containing: like tyrosine, serine 2. Sulfur containing amino acids: like cysteine and methionine From the above data, we can find many amino acids which come in more than one category as follows: img

Glutamic acid is an ?-amino acid, and a dicarboxylic acid. It is a polar, negatively charged amino acid. Glutamate is conjugate base of glutamic acid. The amino acid pays an important role in several metabolic functions like transamination reactions and transport of amino groups. The titration curve for glutamate is as follows: img pK1 = 2.2 (of carboxyl group), pK2 = 9.5 (of ammonium ion) and pK3 = 4.1 (of side chain)The various charged forms of glutamate at different pK values are as follows: img

A buffer is a solution that contains a weak acid and its conjugate base. It resists pH change within a range of the buffer, about 1 pH unit on either side of the pKa of the conjugate acid. The buffering capacity is otherwise defined as the pH of the equimolar solution of acid equal to its pKa. This region most effectively resists pH changes. The Henderson-Hasselbalch Equation is as follows: img According to this equation pH is directly proportional to pK a. This means that an increase or decrease of the pK a by 1 unit, pH will also get affected by 1 unit.