Confirmed Misconceptions in CB-02 Topics
MISCONCEPTION 1: "Enzymes increase to drive reactions." REALITY: Enzymes do NOT alter . is fixed by the thermodynamic properties of reactants and products. Enzymes only lower the activation energy barrier (kinetic effect, not thermodynamic).
MISCONCEPTION 2: "Ribozymes are enzymes made of both RNA and protein." REALITY: Ribozymes are PURELY RNA molecules with catalytic activity. They contain NO protein component. Examples: Group I and II self-splicing introns, RNase P (the RNA subunit is catalytic), peptidyl transferase (23S/28S rRNA).
MISCONCEPTION 3: "Denaturation breaks peptide bonds." REALITY: Denaturation disrupts NON-COVALENT bonds (hydrogen bonds, hydrophobic, ionic), unfolding secondary and tertiary structure. Peptide bonds (primary structure) are covalent and require chemical hydrolysis (not denaturation) to break.
MISCONCEPTION 4: "Sucrose has a free reducing group." REALITY: Sucrose is non-reducing. Both potential reducing groups (aldehyde of glucose and ketone of fructose) are involved in the glycosidic bond formation. This leaves NO free reducing group. Sucrose gives negative Fehling's test.
MISCONCEPTION 5: "A lower Km means the enzyme is slower." REALITY: Km reflects AFFINITY, not speed. Lower Km = higher affinity (enzyme reaches half-maximum velocity at lower substrate concentration). The actual speed depends on Vmax and kcat (turnover number).
MISCONCEPTION 6: "Adding an enzyme to a reaction at equilibrium will shift equilibrium toward products." REALITY: At equilibrium, the forward and reverse rates are EQUAL. An enzyme accelerates BOTH equally. The equilibrium position (Keq) is unchanged. The enzyme just helps the system reach equilibrium faster if disturbed.
MISCONCEPTION 7: "Phospholipids are the same as triglycerides with an added phosphate." REALITY: Phospholipids are fundamentally different: they have only 2 fatty acids (not 3), and the third position on glycerol is occupied by a phosphate group + head group. This changes their properties from entirely non-polar (triglyceride) to amphipathic (phospholipid).
MISCONCEPTION 8: "Trypsin works in the stomach." REALITY: Trypsin works in the SMALL INTESTINE (optimum pH 8). Pepsin works in the STOMACH (optimum pH 2). These are frequently reversed in NEET multiple choice traps.
MISCONCEPTION 9: "Competitive inhibition permanently inactivates the enzyme." REALITY: Competitive inhibition is REVERSIBLE. The inhibitor can be displaced by excess substrate. Irreversible inhibition (e.g., aspirin on COX) permanently inactivates the enzyme by covalent modification.
MISCONCEPTION 10: "Glycogen is found in plants." REALITY: Glycogen is found in ANIMALS (liver and muscle). Plants store energy as STARCH. Both use alpha-glycosidic bonds but glycogen is more highly branched.
MISCONCEPTION 11: "FAD and N are prosthetic groups because they are bound to enzymes." REALITY: N and FAD are COENZYMES (loosely bound, organic). PROSTHETIC GROUPS (e.g., haem) are tightly/covalently bound. The key distinction is binding strength, not the mere fact of association with an enzyme.
MISCONCEPTION 12: "All proteins have quaternary structure." REALITY: Quaternary structure only exists when a protein has TWO OR MORE polypeptide chains. Single-chain proteins (myoglobin, lysozyme, ribonuclease) have no quaternary structure. Haemoglobin (4 chains) is the classic quaternary structure example.
MISCONCEPTION 13: "Chitin and cellulose have the same monomer." REALITY: Cellulose monomer = glucose. Chitin monomer = N-acetylglucosamine (glucose modified with an acetyl-amino group at C-2). Both use beta-1,4 glycosidic bonds, but the monomers differ in chemical composition.
MISCONCEPTION 14: "RNA cannot have secondary structure because it is single-stranded." REALITY: Single-stranded RNA can fold back on itself and form intramolecular base pairs, creating secondary structures (stems and loops). tRNA cloverleaf and rRNA complex folds are examples. Ribozymes depend on their secondary/tertiary structure for catalytic activity.
MISCONCEPTION 15: "Enzymes are consumed during the reaction." REALITY: Enzymes are BIOLOGICAL CATALYSTS — they are NOT consumed. After each catalytic cycle, the enzyme is regenerated and can catalyse the next reaction. This is fundamental to the definition of a catalyst (a substance that speeds up a reaction without being consumed). The enzyme-substrate complex forms and dissociates, releasing free enzyme after product formation.
MISCONCEPTION 16: "Higher substrate concentration always increases enzyme activity indefinitely." REALITY: Enzyme activity reaches a MAXIMUM (Vmax) when all active sites are saturated. Beyond this substrate concentration, adding more substrate has no effect — the rate is limited by enzyme concentration and turnover rate (kcat), not substrate availability.