Enzymes — Active site, specificity
Biomolecules
8
JEE Qs
8%
Hard
75
min
Focus on distinguishing between the 'Lock and Key' and 'Induced Fit' models and understanding how the active site's structure dictates enzyme specificity and function.
✅ Key Points for JEE
- 1Enzymes are highly efficient biocatalysts, predominantly globular proteins, which accelerate biochemical reactions by lowering activation energy without being consumed.
- 2The active site is a specific three-dimensional region (often a cleft or pocket) on the enzyme where the substrate binds and the catalytic reaction occurs; its unique spatial arrangement and functional groups are crucial.
- 3Enzyme specificity refers to the ability of an enzyme to catalyze only one specific reaction or act on a specific type of substrate, arising from the precise complementary fit between the active site and the substrate(s).
- 4The 'Lock and Key' model proposes a rigid active site perfectly complementary to the substrate, while the 'Induced Fit' model suggests a more flexible active site that adapts its shape upon substrate binding to achieve optimal fit.
- 5Specificity can be absolute (for a single substrate), group (for a specific type of bond or functional group), or stereochemical (for a particular stereoisomer).
⚠️ Common Mistakes
- ✕Confusing the 'Lock and Key' model (rigid active site) with the 'Induced Fit' model (flexible active site), and not understanding that Induced Fit provides a more accurate representation of dynamic enzyme-substrate interaction.
- ✕Overlooking the three-dimensional nature and the specific arrangement of amino acid residues within the active site that dictates both specificity and catalytic activity.
- ✕Failing to connect the concept of specificity to the enzyme's role in complex biochemical pathways, where selective action prevents unwanted side reactions.
📝 Practice Questions
See allQ51.Given below are two statements: Statement I: Fructose does not contain an aldehydic group but still reduces Tollen's reagent Statement II: In the presence of base, fructose undergoes rearrangement to give glucose. In the light of the above statements, choose the correct answer from the options given below (1) Both Statement I and Statement II are true (2) Both Statement I and Statement II are false (3) Statement I is true but Statement II is false (4) Statement I is true but Statement II is false
Q51.The carbohydrate "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in ∝-anomeric form Choose the correct answer from the 2025 (24 Jan Shift 1) JEE Main Previous Year Paper options given below: (1) A, D and E Only (2) A, C and D Only (3) A, B and E Only (4) B, D and E Only
Q60.Which of the following acids is a vitamin? (1) Adipic acid (2) Ascorbic acid (3) Saccharic acid (4) Aspartic acid
Q61.Identify the number of structure/s from the following which can be correlated to D-glyceraldehyde. (1) four (2) one (3) two (4) three
Q59.The α-Helix and β - Pleated sheet structures of protein are associated with its : (1) tertiary structure (2) quaternary structure (3) secondary structure (4) primary structure ∣∣∣ ∣∣∣ ∣∣∣ ∣∣ 2025 (23 Jan Shift 2) JEE Main Previous Year Paper
Q51.Given below are two statements: Statement I : D-glucose pentaacetate reacts with 2, 4-dinitrophenylhydrazine Statement II : Starch, on heating with concentrated sulfuric acid at 100∘C and 2-3 atmosphere pressure produces glucose. In the light of the above statements, choose the correct answer from the options given below 2025 (28 Jan Shift 1) JEE Main Previous Year Paper (1) Statement I is false but Statement II is true (2) Both Statement I and Statement II are false (3) Both Statement I and Statement II are true (4) Statement I is true but Statement II is false
NCERT Chapters
- Class 12 Chemistry Ch 14: Biomolecules