Micromolecules vs Macromolecules (Biomacromolecules)
Biology · Biomolecules · NEET
Micromolecules are small biomolecules with molecular weight less than 1000 daltons (Da) and stay in the acid-soluble pool. Macromolecules (biomacromolecules) are big, with molecular weight 10,000 Da and above, and stay in the acid-insoluble fraction. Memory hook: "Micro is Money-light (under 1000), Macro is Massive (over 10,000)."
Grinding tissue in acid and filtering splits biomolecules into the acid-soluble pool (micromolecules, under 1000 Da) and the acid-insoluble fraction (macromolecules, 10,000 Da and above). *Lipids are light but join the macromolecular fraction because they form membrane vesicles.
Your doubts, answered
What molecular weight separates micromolecules from macromolecules?
NCERT gives a clear cut-off. Micromolecules have molecular weight less than 1000 Da (the acid-soluble pool ranges from about 18 to 800 Da). Macromolecules have molecular weight of about 10,000 Da and above (the acid-insoluble fraction). For NEET, remember the two numbers: below 1000 = micro, 10,000 and above = macro.
Which four compounds are the macromolecules (biomacromolecules)?
The acid-insoluble fraction has only FOUR types of organic compounds: proteins, nucleic acids, polysaccharides, and lipids. NCERT calls these biomacromolecules. This is a common NEET fact question, so memorise the four.
Are lipids micromolecules or macromolecules? This confuses students.
By molecular weight alone, lipids are small (less than 800 Da), so they seem like micromolecules. But NCERT places lipids in the acid-insoluble (macromolecular) fraction. Reason: during grinding, lipids form membrane vesicles that are too big to pass the filter, so they end up with the retentate. So lipids are counted as macromolecules for classification even though each lipid molecule is light.
Are all macromolecules polymers?
No. Proteins, nucleic acids and polysaccharides are true polymers (made of repeating monomer units). Lipids are NOT polymers, they are esters of fatty acids and glycerol. So the acid-insoluble fraction is polymeric EXCEPT for lipids. NEET 2017 tested exactly this.
What is the acid-soluble pool?
When you grind a tissue in acid (like trichloroacetic acid) and filter it, the filtrate is the acid-soluble pool. It holds thousands of small organic compounds (amino acids, sugars, nucleotides) with molecular weights 18 to 800 Da. These are the micromolecules. The leftover retentate is the acid-insoluble fraction holding the macromolecules.
Are micromolecules also just called biomolecules?
Yes. NCERT says micromolecules are usually referred to simply as biomolecules, while the large acid-insoluble ones are called macromolecules or biomacromolecules. So in NCERT language, 'biomolecule' in the narrow sense often means the small micromolecule.
⚠️ The NEET trap ✗ Lipids are micromolecules because their molecular weight is under 800 Da, so they are non-polymeric and belong to the acid-soluble pool. ✓ Lipids have small molecular weight, but NCERT places them in the acid-insoluble (macromolecular) fraction because they form membrane vesicles that do not pass the filter. Lipids are the only non-polymeric member of the four macromolecules. 🧠 NEET tests the split idea: lipids are LIGHT in weight but sit in the HEAVY (macromolecular) fraction. Weight says micro, fraction says macro. Do not mix the two rules.
Real NEET questions
NEET 2017
Which of the following are not polymeric?
A · Nucleic acids
B · Proteins
C · Polysaccharides
D · Lipids ✓
Solution: Nucleic acids (polymers of nucleotides), proteins (polymers of amino acids) and polysaccharides (polymers of monosaccharides) are true polymeric biomacromolecules. Lipids are esters of fatty acids with glycerol and are not built from repeating monomer units, so they are NOT polymeric. This is why NCERT calls the acid-insoluble fraction polymeric 'with the exception of lipids'.
NEET 2024
Lecithin, a small molecular weight organic compound found in living tissues, is an example of
A · Phospholipids ✓
B · Glycerides
C · Carbohydrates
D · Amino acids
Solution: Lecithin is a small molecular weight lipid containing a phosphorylated group; NCERT names it as a phospholipid found in cell membranes. Note the phrase 'small molecular weight' links to the micromolecule idea, yet as a lipid it still classifies with the macromolecular (acid-insoluble) fraction.
Solved Biomolecules NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Water is a micromolecule. Its molecular weight is only 18 Da, which is the lowest end of the acid-soluble pool range (18 to 800 Da). Water is also the most abundant molecule in living cells.
Why do lipids fall in the macromolecular fraction despite low weight?
During tissue grinding, lipids form membrane-bound structures (vesicles) that are large and get trapped in the retentate, so they end up in the acid-insoluble macromolecular fraction even though each molecule is under 800 Da.
What is the molecular weight range of the acid-soluble pool?
About 18 to 800 daltons. These are all micromolecules such as amino acids, sugars, nucleotides and organic acids.
Do macromolecules include DNA and RNA?
Yes. Nucleic acids (DNA and RNA) are one of the four macromolecules, along with proteins, polysaccharides and lipids. DNA and RNA are polymers of nucleotides.
Is starch a micromolecule or macromolecule?
Starch is a macromolecule. It is a polysaccharide, a polymer of many glucose units, with molecular weight in the tens of thousands of daltons, so it sits in the acid-insoluble fraction.
