Question

Differentiate between the following:

(i) Peptide linkage and Glycosidic linkage

(ii) Essential amino acids and Non-essential amino acids

Hint:

A linkage is the type of bond that joins the small building-block units of a biomolecule. Different biomolecules use different linkages, and amino acids are classified by whether or not our body can make them.

Answer 1

Concept:
A linkage is the type of bond that joins the small building-block units of a biomolecule. Different biomolecules use different linkages, and amino acids are classified by whether or not our body can make them.

Step 1 (part i - Peptide vs Glycosidic linkage):
A peptide linkage is the amide bond (-CO-NH-) that joins two amino acids. It forms when the carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH2) of another amino acid with loss of a water molecule. Peptide linkages join amino acids to build proteins.
A glycosidic linkage is the C-O-C bond that joins two monosaccharide (sugar) units. It forms when the -OH group of one sugar reacts with the -OH group of another sugar with loss of a water molecule. Glycosidic linkages join sugars to build carbohydrates such as sucrose and starch.

Step 2 (part ii - Essential vs Non-essential amino acids):
Essential amino acids are those which the human body cannot make on its own, so they must be supplied through our diet (food). Examples: valine, leucine, lysine.
Non-essential amino acids are those which the human body can make on its own (synthesise in the body), so they need not be taken from food. Examples: glycine, alanine.

Answer:
(i) A peptide linkage is the amide (-CO-NH-) bond joining two amino acids in proteins (formed with loss of water), whereas a glycosidic linkage is the C-O-C bond joining two monosaccharide units in carbohydrates (also formed with loss of water).
(ii) Essential amino acids cannot be made by the body and must come from the diet (e.g. valine, lysine), whereas non-essential amino acids can be made by the body itself (e.g. glycine, alanine).