Which moieties of nucleosides are involved in the formation of phosphodiester linkages present in dinucleotides? What does the word diester in the name of linkage indicate? Which acid is involved in the formation of this linkage?
(i) $5^{\prime}$ and $3^{\prime}$ carbon atoms of pentose sugar.
(ii) Most probably the resemblance of with 2 ester $(-\mathrm{COO})^{2-}$ groups joined together.
(iii) Phosphoric acid $\left(\mathrm{H}_3 \mathrm{PO}_4\right)$.
Nucleosides are joined together by phosphodiester linkage between $5^{\prime}$ and $3^{\prime}$ carbon atoms of pentose sugar and a dinucleotide with phosphoric acid $\left(\mathrm{CH}_3 \mathrm{PO}_4\right)$ is formed
What are glycosidic linkages? In which type of biomolecules are they present?
Linkage between two monosaccharides due to oxide linkage formed by the loss of a water molecule, is known as glycosidic linkage as shown below
Which monosaccharide units are present in starch, cellulose and glucose and which linkages link these units?
Monosaccharides units present in starch, cellulose and glucose can be determined by knowing the product of their hydrolysis.
(i) Starch is a polysaccharide of $\alpha$-glucose in which two types of linkage are observed i.e., $\mathrm{C}_1-\mathrm{C}_6$ and $\mathrm{C}_1-\mathrm{C}_4$ glycosidic linkage.
(ii) Cellulose is a straight chain polysaccharide of $\beta$-D glucose in which glucose are linked together by $\mathrm{C}_1-\mathrm{C}_4$ glycosidic linkage.
(iii) Glucose is a monosaccharide.
How do enzymes help a substrate to be attacked by the reagent effectively?
At the surface of enzyme, active sites are present. These active sites of enzymes hold the substrate molecule in a suitable position, so that it can be attacked by the reagent effectively. This reduces the magnitude of activation energy.
Enzymes contains cavities of characteristics shape and possessing active groups known as active centre on the surface. The molecules of the reactant (substrate) having complementary shape, fit into these cavities. On account of these active groups, an activated complex is formed which then decomposes to yield the products.
Describe the term D- and L-configuration used for amino acids with examples.
All naturally occurring $\alpha$-amino acids (except glycine) are optically active due to the presence of chiral carbon atom. These have either $D$ - or L-configuration. $D$-form means that, the amino $\left(-\mathrm{NH}_2\right)$ group is present towards the right hand side. $L$-form shows the presence of $-\mathrm{NH}_2$ group on the left hand side.
