BIOMOLECULES AND ENZYMES

Detailed explanation-1: -In the human body, there are 20 amino acids that function as building blocks of proteins. Nine of these amino acids are considered essential-they must be consumed in the diet-while five are considered nonessential in that they can be made by the human body.

Detailed explanation-2: -There are 22 amino acids that are found in proteins and of these, only 20 are specified by the universal genetic code. The others, selenocysteine and pyrrolysine use tRNAs that are able to base pair with stop codons in the mRNA during translation.

Detailed explanation-3: -Pyrrolysine: the 22nd amino acid pyrrolysine (Pyl, O) is a genetically encoded amino acid that occurs naturally in methanogenic archaea, now designated the 22nd amino acid.

Detailed explanation-4: -Both animal and plant proteins are made up of about 20 common amino acids. The proportion of these amino acids varies as a characteristic of a given protein, but all food proteins-with the exception of gelatin-contain some of each.

Detailed explanation-5: -A protein molecule is made from a long chain of these amino acids, each linked to its neighbor through a covalent peptide bond (Figure 3-1). Proteins are therefore also known as polypeptides. Each type of protein has a unique sequence of amino acids, exactly the same from one molecule to the next.