BIOMOLECULES · Comparison Tables

1. Acid-Soluble Pool vs Acid-Insoluble Fraction

Feature	Acid-soluble pool / filtrate	Acid-insoluble fraction / retentate
Preparation	Filtrate obtained after tissue is ground in trichloroacetic acid and strained	Material retained after straining
Typical molecular mass	About 18 to 800 Da; usually less than 1000 Da	True macromolecules generally above 10,000 Da
Representative contents	Amino acids, sugars, fatty acids, glycerol, nitrogen bases, nucleosides, nucleotides, ions and inorganic compounds	Proteins, nucleic acids, polysaccharides and lipids
Cellular representation	Roughly cytoplasmic composition	Macromolecules from cytoplasm and organelles
Important exception	Lipids are small molecules but occur in the insoluble fraction because broken membranes form water-insoluble vesicles.

2. Primary Metabolites vs Secondary Metabolites

Feature	Primary metabolites	Secondary metabolites
Occurrence	Seen in animal tissues and all normal living cells	Especially abundant in plant, fungal and microbial cells
Role	Identifiable functions in normal physiological processes	Functions in host organism are not always fully understood; many have ecological importance
Examples	Amino acids, sugars, fatty acids, glycerol, nucleotides and proteins	Alkaloids, flavonoids, rubber, essential oils, antibiotics, pigments, gums and spices
Human relevance	Core compounds of metabolism	Useful products include drugs, scents, pigments, rubber and spices

3. Amino Acids: Acidic vs Basic vs Neutral

Class	Basis	NCERT example
Acidic amino acid	Acidic character from number/nature of amino and carboxyl groups	Glutamic acid
Basic amino acid	Basic character from number/nature of amino and carboxyl groups	Lysine
Neutral amino acid	Neither acidic nor basic in this classification	Valine
Aromatic amino acid	Contains aromatic R group	Tyrosine, phenylalanine and tryptophan
Shared plan	Protein amino acids are alpha-amino acids: alpha-carbon bears H, -NH₂, -COOH and a variable R group. Their ionisable groups permit zwitterionic form at suitable pH.

4. Saturated vs Unsaturated Fatty Acids; Fats vs Oils

Feature	Saturated fatty acid / fat	Unsaturated fatty acid / oil
Carbon-carbon bonds	No C=C double bond in fatty-acid chain	One or more C=C double bonds
Melting point and state	Higher melting point; commonly solid as fat	Lower melting point; commonly liquid as oil
Glyceride formation	Fatty acids esterify with glycerol (trihydroxy propane) to form mono-, di- and triglycerides.
Phospholipid link	Phospholipids contain phosphorus and a phosphorylated organic compound; lecithin is an example and is found in cell membranes.

5. Nucleoside vs Nucleotide; DNA vs RNA

Feature	Nucleoside	Nucleotide
Composition	Nitrogenous base + sugar	Nitrogenous base + sugar + phosphate
Examples	Adenosine, guanosine, thymidine, uridine and cytidine	Adenylic, guanylic, thymidylic, uridylic and cytidylic acids
Polymer role	Component without phosphate	Building block of DNA and RNA

Feature	DNA	RNA
Sugar	2'-deoxyribose	Ribose
Full name	Deoxyribonucleic acid	Ribonucleic acid
Shared plan	Both are nucleic acids/polynucleotides. Purines are adenine and guanine; pyrimidines are cytosine, uracil and thymine.

6. Major Polysaccharides Compared

Polysaccharide	Monomer / structure	Main occurrence or role
Cellulose	Glucose homopolymer; no complex helix that holds iodine	Plant cell wall; cotton and paper are cellulosic
Starch	Glucose polymer with helical regions; holds I₂ and turns blue	Energy store in plants
Glycogen	Branched sugar polymer with reducing and non-reducing ends	Energy store in animals
Inulin	Polymer of fructose	Plant storage carbohydrate
Chitin	Complex polysaccharide with amino/modified sugars	Arthropod exoskeleton

7. Levels of Protein Structure

Level	Description	Key term / example
Primary	Linear positional sequence of amino acids	N-terminal amino acid at one end; C-terminal amino acid at the other
Secondary	Local folding of the protein thread	Right-handed alpha helix; other folded forms
Tertiary	Further folding of a long polypeptide into a three-dimensional form	Essential for many biological activities
Quaternary	Arrangement of more than one folded polypeptide subunit	Adult human haemoglobin: 2 alpha + 2 beta subunits

8. Enzymes: Regulation and Cofactors

Topic	Key distinction / NCERT fact
Enzyme vs ribozyme	Almost all enzymes are proteins; catalytic nucleic acids are ribozymes.
Active site and activation energy	Substrate fits in active-site pocket. Enzymes lower activation energy, accelerating conversion through the transition state.
Low vs high temperature	Low temperature makes enzymes temporarily inactive; high temperature denatures protein and destroys activity.
Substrate concentration	Velocity rises then reaches V_max when enzyme molecules are saturated.
Competitive inhibition	Inhibitor resembles substrate and competes for the binding site; malonate inhibits succinate dehydrogenase.
Prosthetic group vs coenzyme	Prosthetic group is tightly bound (haem in catalase/peroxidase); coenzyme associates transiently (NAD/NADP contain niacin).
Metal-ion cofactor	Metal ions coordinate active site and substrate; zinc is needed by carboxypeptidase.

Six enzyme classes Oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases.