Exam Master Review Sheet - Biomolecules

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EXAM MASTER REVIEW SHEET

Biomolecules

Carbohydrates, Proteins, Nucleic Acids & Vitamins

1. Carbohydrates (Saccharides)

Polyhydroxy aldehydes or ketones, or compounds which produce them on hydrolysis.

Classification

• Monosaccharides: Cannot be hydrolyzed (Glucose, Fructose).
• Oligosaccharides: Yield 2-10 units (Sucrose, Lactose).
• Polysaccharides: Yield many units (Starch, Cellulose).

Reducing vs Non-Reducing

Reducing: Free aldehyde/ketone group. Reduces Tollen's/Fehling's (All monosaccharides, Maltose).

Non-Reducing: Sucrose (Glycosidic linkage involves both anomeric carbons).

Chemical Evidence for Glucose Structure

1. HI / $\Delta$: Forms n-hexane (Shows straight chain).

2. $NH_2OH$: Forms oxime (Shows Carbonyl group).

3. $Br_2 / H_2O$: Forms Gluconic acid (Shows Aldehyde group).

4. $(CH_3CO)_2O$: Forms pentaacetate (Shows 5 $-OH$ groups).

5. $HNO_3$: Forms Saccharic acid (Shows Primary $-OH$ group).

2. Amino Acids & Peptide Bond

Building blocks of proteins containing both $-NH_2$ and $-COOH$ groups.

Zwitterion Property

In aqueous solution, $-COOH$ loses a proton and $-NH_2$ gains one.

$H_3N^+ - CH(R) - COO^-$

At Isoelectric Point (pI), net charge is zero; minimum solubility.

Peptide Linkage

An amide linkage ($-CO-NH-$) formed between $-COOH$ of one amino acid and $-NH_2$ of another.

Essential Amino Acids: Must be taken in diet (Val, Leu, Ile, Lys, etc.).

3. Protein Structures

Level	Description	Stabilizing Forces
Primary ($1^\circ$)	Sequence of amino acids.	Peptide bonds (Covalent).
Secondary ($2^\circ$)	$\alpha$-Helix or $\beta$-Pleated sheet.	Intramolecular H-bonding.
Tertiary ($3^\circ$)	Overall folding (Fibrous/Globular).	Disulphide, H-bonds, van der Waals.

Denaturation of Proteins

Change in $T$ or $pH$ disrupts $2^\circ$ and $3^\circ$ structures. $1^\circ$ structure remains intact. Biological activity is lost (e.g., coagulation of egg white).

4. Nucleic Acids (DNA & RNA)

Composition

• Nucleoside: Base + Sugar.
• Nucleotide: Base + Sugar + Phosphate.
• Bases: Purines (A, G) & Pyrimidines (C, T, U).

Key Differences

DNA: 2-deoxyribose sugar; Bases: A, G, C, T.
RNA: Ribose sugar; Bases: A, G, C, U.

Chargaff's Rule: In DNA, $[A] = [T]$ and $[G] = [C]$.

5. Qualitative Identification Tests

For Carbohydrates

• Molisch Test: Violet ring at junction (General test).
• Seliwanoff Test: Cherry red color (Distinguishes Ketohexose).
• Barfoed Test: Distinguishes Monosaccharides.

For Proteins

• Biuret Test: Bluish-violet color (Peptide bonds).
• Ninhydrin Test: Intense Blue/Purple (Amino acids).
• Xanthoproteic Test: Yellow color (Aromatic amino acids).

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