Key Reactions and Data — Biomolecules — Summary

Carbohydrate Reactions

Reaction	Reagent	Positive Result	Sugars That React
Tollens' test	$Ag(NH_3)_2^+$ (ammoniacal AgNO $_3$ )	Silver mirror	All reducing sugars
Fehling's test	Cu $^{2+}$ (alkaline)	Brick-red Cu $_2$ O precipitate	All reducing sugars
Iodine test	I $_2$ /KI solution	Blue-black colour	Starch (amylose) only
Benedict's test	Cu $^{2+}$ citrate (alkaline)	Orange-red precipitate	All reducing sugars
Hydrolysis of sucrose	Invertase / dilute acid	Glucose + Fructose (invert sugar)	Sucrose only
Hydrolysis of starch	Amylase	Maltose, then glucose	Starch

Peptide Bond Formation

$\text{H}_2\text{N–CHR}_1\text{–COOH} + \text{H}_2\text{N–CHR}_2\text{–COOH} \xrightarrow{-H_2O} \text{H}_2\text{N–CHR}_1\text{–CO–NH–CHR}_2\text{–COOH}$

Conditions: condensation (elimination of water); reversible by hydrolysis (acid/base/enzyme).

Hydrogen Bond Data in DNA

Base Pair	H-bonds	Relative Stability
A–T (Adenine–Thymine)	2	Lower $T_m$
G–C (Guanine–Cytosine)	3	Higher $T_m$

Vitamin Formula References

Vitamin	Formula	Key Element
B12 (Cyanocobalamin)	$C_{63}H_{88}CoN_{14}O_{14}P$	Contains cobalt (Co)
Folic acid (B9)	$C_{19}H_{19}N_7O_6$	Pteridine ring
Ascorbic acid (C)	$C_6H_8O_6$	Lactone of hexuronic acid
Retinol (A)	$C_{20}H_{30}O$	Isoprenoid chain

Key Molecular Formulas

$\text{Glucose/Fructose/Galactose}: C_6H_{12}O_6$ $\text{Sucrose}: C_{12}H_{22}O_{11} \quad \text{(disaccharide, } -H_2O \text{ from two hexoses)}$ $\text{Starch/Cellulose/Glycogen}: (C_6H_{10}O_5)_n$