CHEMCA
EXAM MASTER REVIEW SHEET
Biomolecules
1 Carbohydrates (Saccharides)
Optically active polyhydroxy aldehydes or ketones, or compounds which produce them on hydrolysis.
Reducing Sugars: Have a free aldehyde or ketone group. They reduce Tollen's and Fehling's solutions. (e.g., All Monosaccharides, Maltose, Lactose).
Non-Reducing Sugars: Aldehydic/Ketonic groups are bonded in glycosidic linkage. e.g., Sucrose.
Glucose exists in two cyclic forms ($\alpha$ and $\beta$) called Anomers. They differ only in the configuration of the $-OH$ group at $C_1$ (Anomeric Carbon).
Mutarotation: Spontaneous change in specific rotation of an optically active compound to an equilibrium value.
Chemical Evidence for D-Glucose Structure
$HI / \Delta$ $\rightarrow$ Yields n-hexane. (Proves straight 6-C chain)
$NH_2OH$ / $HCN$ $\rightarrow$ Oxime / Cyanohydrin. (Proves Carbonyl $>C=O$ group)
$Br_2$ water $\rightarrow$ Gluconic acid. (Mild oxidation proves Aldehyde group)
$HNO_3$ $\rightarrow$ Saccharic acid. (Strong oxid. proves $1^\circ$ Alcohol at tail)
$(CH_3CO)_2O$ $\rightarrow$ Pentaacetate. (Proves presence of 5 $-OH$ groups)
| Disaccharide / Polysaccharide | Monomer Units | Glycosidic Linkage Type (High Yield) |
|---|---|---|
| Sucrose (Invert Sugar) | $\alpha$-D-Glucose + $\beta$-D-Fructose | $C_1$ of Glu - $C_2$ of Fru |
| Maltose | Two $\alpha$-D-Glucose units | $C_1$ of Glu - $C_4$ of Glu |
| Lactose (Milk Sugar) | $\beta$-D-Galactose + $\beta$-D-Glucose | $C_1$ of Gal - $C_4$ of Glu |
| Starch (Amylose - 15%) | $\alpha$-D-Glucose (Linear) | $\alpha$ $1 \rightarrow 4$ glycosidic linkage |
| Starch (Amylopectin - 85%) | $\alpha$-D-Glucose (Branched) | $\alpha$ $1 \rightarrow 4$ chain, $\alpha$ $1 \rightarrow 6$ branching |
| Cellulose | $\beta$-D-Glucose (Linear) | $\beta$ $1 \rightarrow 4$ glycosidic linkage |
2 Amino Acids & Proteins
Building blocks of proteins containing both acidic ($-COOH$) and basic ($-NH_2$) groups. All naturally occurring $\alpha$-amino acids are optically active except Glycine.
$H_3N^+ - CH(R) - COO^-$
Zwitterion: Dipolar, neutral ion.
Isoelectric Point (pI): The pH at which the amino acid carries no net electrical charge. Solubility is minimum here.
- $1^\circ$ Structure: The specific sequence of amino acids linked by covalent peptide bonds ($-CO-NH-$).
- $2^\circ$ Structure: Regular folding ($\alpha$-helix or $\beta$-pleated sheet) stabilized by intramolecular Hydrogen bonds.
- $3^\circ$ Structure: Overall 3D folding of the chain. Stabilized by H-bonds, Disulphide linkages ($-S-S-$), van der Waals, and electrostatic forces.
3 Vitamins (Essential Factors)
| Vitamin | Chemical Name | Solubility | Deficiency Disease (Highly Tested) |
|---|---|---|---|
| Vitamin A | Retinol | Fat | Night blindness, Xerophthalmia |
| Vitamin B1 | Thiamine | Water | Beri-Beri (loss of appetite, stunted growth) |
| Vitamin B12 | Cyanocobalamin (Contains Cobalt) |
Water | Pernicious Anaemia (RBC deficiency) |
| Vitamin C | Ascorbic Acid | Water | Scurvy (bleeding gums) |
| Vitamin D | Calciferol | Fat | Rickets (children), Osteomalacia (adults) |
| Vitamin E | Tocopherol | Fat | Muscular weakness, increased RBC fragility |
| Vitamin K | Phylloquinone | Fat | Increased blood clotting time |
Note: Vitamin B and C are water-soluble and must be supplied regularly in diet as they are excreted in urine (except B12 which is stored in liver).
4 Nucleic Acids (DNA & RNA)
Components & Linkages
- Nucleoside: Nitrogenous Base + Pentose Sugar (attached at C1' via N-glycosidic linkage).
- Nucleotide: Nucleoside + Phosphoric acid (attached at C5' via Phosphoester linkage).
Nucleotides are joined together by Phosphodiester linkages between the 5' and 3' carbon atoms of the pentose sugar.
DNA vs. RNA
• Sugar: $\beta$-D-2-deoxyribose
• Bases: Adenine, Guanine, Cytosine, Thymine.
• Sugar: $\beta$-D-ribose
• Bases: Adenine, Guanine, Cytosine, Uracil.
Chargaff's Rule (DNA): Adenine = Thymine ($A=T$), Guanine = Cytosine ($G \equiv C$)
5 Qualitative Biomolecule Tests
- Molisch's Test: General test for all carbs. Gives a Reddish-violet ring at the junction of two layers.
- Seliwanoff's Test: Distinguishes ketoses from aldoses. Ketoses (like Fructose) give a Cherry red color rapidly.
- Barfoed's Test: Distinguishes monosaccharides from disaccharides. Monosaccharides reduce copper acetate rapidly.
- Biuret Test: Detects peptide bonds. Addition of dilute $CuSO_4$ in alkaline medium yields a Bluish-violet color.
- Ninhydrin Test: General test for amino acids. Forms an intense Blue/Purple color complex (Ruhemann's purple).
- Xanthoproteic Test: Concentrated $HNO_3$ is added to protein giving a Yellow precipitate. (Detects aromatic amino acids like Tyrosine, Tryptophan).
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