2.5.7 · HinglishEnzymes & Bioenergetics Basics
Explain the induced-fit model
2.5.7· Biology › Enzymes & Bioenergetics Basics
WHAT is the induced-fit model?
Key contrast:
- Lock-and-key (Fischer, 1894): active site rigid hota hai; substrate ek key ki tarah lock mein fit hota hai.
- Induced-fit (Koshland): active site flexible hota hai; binding ise reshape karti hai.
WHY do we need induced fit? (Pehle lock-and-key ko steel-man karte hain)
Lock-and-key sahi lagta hai kyunki:
- Enzymes specific hote hain — ek enzyme, ek substrate. Ek rigid pre-shaped pocket specificity ko cleanly explain karta hai.
Lekin yeh kuch observations explain karne mein fail hota hai:
Toh induced fit dono specificity aur catalytic power explain karta hai.
HOW does it work, step by step?
- Substrate open active site ke paas aata hai.
- Initial weak bonds (H-bonds, ionic, van der Waals) bante hain.
- Ye contacts enzyme ko strain karte hain, ek hinge-jaisa conformational change trigger karte hue.
- Active site close hota hai, catalytic residues align hote hain + substrate strain hota hai apne transition state ki taraf.
- Bonds toote/bane → products bante hain, jo ab fit nahi karte → site reopen hoti hai aur unhe release karti hai.
Thodi si energetics: WHY straining helps
Worked Examples
Common Mistakes
Active Recall
Recall Quick self-test (dekhne se pehle try karo)
- Induced fit kisne propose kiya, aur usne kaunse model ko refine kiya?
- Enzyme ka kaunsa part shape change karta hai, aur kya trigger karta hai?
- Induced fit sirf substrate hold karne se zyada rate kaise badhata hai?
- Hexokinase ka closure ATP waste kyun rokta hai?
Recall Feynman: 12-saal ke bacche ko explain karo
Ek beanbag chair (enzyme) aur tum (substrate) ki tarah socho. Ek ordinary chair ki fixed shape hoti hai — woh lock-and-key hai. Lekin ek beanbag sirf tab squish hokar tumhare around wrap hota hai jab tum actually baithte ho. Woh hugging tumhe bilkul sahi position mein settle karti hai. Enzyme ek molecule ke saath yahi karta hai, use squeeze karke perfect shape mein react karne ke liye. Jab molecule kuch naya ban jaata hai, toh woh ab "sahi tarah nahi baithta," toh beanbag wapas puff up ho jaata hai aur agla molecule aa sakta hai.
Connections
- Lock-and-Key Model — woh rigid predecessor jise induced fit refine karta hai
- Enzyme Active Site — jahan conformational change hoti hai
- Activation Energy — jise induced fit kam karta hai
- Transition State Theory — induced fit is state ko stabilise karta hai
- Enzyme Specificity — dono models se explain hoti hai
- Hexokinase and Glycolysis — classic induced-fit example
- Allosteric Regulation — enzyme shape change ka ek aur case
Who proposed the induced-fit model and in what year?
Daniel Koshland ne propose kiya, 1958 mein.
Which earlier model did induced fit refine?
Lock-and-key model (Emil Fischer, 1894).
In induced fit, which molecule's shape primarily changes?
Enzyme ka active site shape change karta hai (mould hota hai) substrate ke around.
What triggers the conformational change in induced fit?
Substrate ka active site se initial weak binding conformational change trigger karta hai.
How does induced fit boost catalysis beyond simple binding?
Yeh substrate ko strain karta hai aur transition state ko stabilise karta hai, activation energy aur bhi kam karta hai.
Why does hexokinase closing around glucose prevent ATP waste?
Closure paani ko bahar rakhta hai, toh ATP bekar mein hydrolyse nahi hota.
Is the enzyme permanently changed after catalysis?
Nahi — yeh reversibly apni original conformation mein wapas aa jaata hai aur reuse hota hai.
Why does the product get released in the induced-fit model?
Product ki alag shape hoti hai, induced fit maintain nahi rehta, toh active site relax hokar open ho jaata hai.
By what relation does lowering activation energy raise rate?
Arrhenius: ; rate enhancement .
What is one observation lock-and-key cannot explain but induced fit can?
Transition-state stabilisation / conformational proofreading (jaise hexokinase sirf glucose ke liye close hona).