(JUNE 2007)
11. The order of reaction catalyzed by enzyme at low substrate concentration is
(1) first order (2) Pseudo first order
(3) Second order (4) Zero order
The correct answer is (1) first order.
Introduction
Enzymes catalyze biochemical reactions by lowering activation energy and increasing reaction rates. However, the order of the reaction catalyzed by enzymes depends on substrate concentration. This concept is pivotal in enzyme kinetics and has profound implications in biochemical pathways and pharmaceutical sciences. Here, the focus is on enzyme-catalyzed reactions at low substrate concentrations and why they follow first-order kinetics.
Understanding Reaction Order in Enzyme Kinetics
The order of a reaction describes how the reaction rate depends on the concentration of reactants.
For a simple reaction without enzymes:
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A first-order reaction rate depends linearly on the concentration of one reactant.
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A second-order reaction depends on the concentration of two reactants.
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A zero-order reaction indicates the rate is independent of substrate concentration.
Enzyme Kinetics: Michaelis-Menten Model
The Michaelis-Menten model describes how the reaction rate (v) depends on substrate concentration [S]:
v=Vmax[S]Km+[S]
Where
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Vmax is the maximum reaction velocity (when enzyme is saturated by substrate).
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Km is the Michaelis constant (substrate concentration at which reaction rate is half of Vmax).
Reaction Order at Low Substrate Concentration ([S]≪Km)
When substrate concentration is very low compared to Km:
v≈Vmax[S]Km∝[S]
This means:
-
The reaction rate is directly proportional to substrate concentration.
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The reaction exhibits first-order kinetics with respect to substrate concentration.
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The enzyme active sites are mostly free, so the substrate availability limits the reaction rate.
Reaction Order at High Substrate Concentration ([S]≫Km)
At high substrate concentrations:
v≈Vmax
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The enzyme becomes saturated with substrate.
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The reaction rate reaches a maximum (Vmax) and no longer increases with substrate concentration.
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Reaction displays zero-order kinetics with respect to substrate concentration.
Real-World Analogy
Imagine taxis (enzymes) waiting for passengers (substrate):
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At low passengers, increasing passengers directly increases trips (first-order).
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At full capacity (enzyme saturation), more passengers do not increase trips (zero-order).
Implications in Biology and Biotechnology
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Understanding the order of enzyme reactions helps predict reaction behavior in metabolic pathways.
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Useful in designing drugs and inhibitors targeting enzyme activity.
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Vital for metabolic engineering and enzyme-based industrial processes.
Summary Table
| Substrate Concentration | Reaction Order | Explanation |
|---|---|---|
| Low ([S]≪Km) | First order | Rate proportional to substrate |
| High ([S]≫Km) | Zero order | Rate independent of substrate (saturation) |
Conclusion
At low substrate concentrations, enzyme-catalyzed reactions follow first-order kinetics because the reaction rate depends on the amount of available substrate. As substrate concentration increases, saturation occurs, shifting the reaction to zero-order kinetics. This fundamental concept is crucial for understanding enzyme behavior in physiological and experimental settings and beneficial for academic and professional pursuits in life sciences.
52 Comments
Roopal Sharma
September 12, 2025First order reaction depends upon substrate concentration and zero order reaction is independent of substrate concentration.
Sakshi yadav
September 12, 2025Ist order of reaction -it’s depend upon the substrate conc.
Aakansha sharma Sharma
September 12, 2025First order reaction bez it depends upon only onesubstrate concentration
Sakshi Kanwar
September 12, 2025At low substrate concentrations, the reaction rate is directly proportional to the substrate concentration.
And reaction will be first order
Varsha Tatla
September 12, 20251st oder reaction
Mohd juber Ali
September 12, 2025At low substrate concentration rate dependebt of subs.(first order reaction )
Priya dhakad
September 12, 2025First order reaction becoz it depends upon substrate concentration.
Mansukh Kapoor
September 12, 2025The correct answer is option 1st
First order reaction is based upon the substrate concentration
Tanvi Panwar
September 12, 2025First order reaction is based on substrate concentration.
Heena Mahlawat
September 12, 20251st order reaction – here the concentration of substrate is low and limiting, hence reaction is dependent on concentration of one reactant only
HIMANI FAUJDAR
September 12, 2025Ans First order reaction depend on one substrate concentration.
Kanica Sunwalka
September 13, 2025first order as it is based on substrate conc .
Santosh Saini
September 13, 20251st order reaction depends linearly on the concentration of one substrate
Dharmpal Swami
September 13, 2025First order rex.at which substrate construction is low
Neha Yadav
September 13, 20251st order of reaction depends on the 1 reactants conc. ( Low Substrate concentration )
Kirti Agarwal
September 13, 2025First order reaction
Bhawna Choudhary
September 13, 20251st order reaction is the correct answer
Bhawna Choudhary
September 13, 20251st order reaction
Soniya Shekhawat
September 14, 2025First order reaction depend on upon substate concentration in which substrate concentration is very low compared to the km .
Nilofar Khan
September 14, 2025correct answer is (1) first order.
First order reaction depend upon substate.
Aafreen Khan
September 14, 2025First Order Reaction because here the concentration of substrate is low and rate depends on the concentration of one reactant
Kajal
September 14, 2025First order bcz depends upon substrate concentration
Ayush Dubey
September 14, 2025first order.
Vanshika Sharma
September 14, 2025First order reaction
Khushi Agarwal
September 14, 2025The correct answer is (1) first order.
Anjali
September 14, 2025First order reaction
Bhavana kankhedia
September 14, 2025First order reaction
Manisha choudhary
September 14, 2025Jab substrate concentration km hoti h too enzyme ki active site free bhi hoti h jaise jaise substrate concentration bdhayenge vese vese enzyme substate complex bhi bnta jayega jab tk ki sabhi enzyme ko substrate nhi mil jaate rate of reaction bdhegi straight line curve hoga means first oder reaction ko follow krega
Jab sbhi enzyme ko substrate mil jaayega at high substrate concentration ab substrate kaa number kitna bhi bdha lo rate of reaction nhi bdhegi means substrate ki concentration p depend nhi rahegi saturation aa jayega zero order reaction ko follow krega
Anurag Giri
September 14, 2025Ans 1 A first-order reaction rate depends linearly on the concentration of one reactant
Mitali saini
September 14, 2025The correct answer is (1) first order.
Avni
September 14, 2025First Order Reaction rate depends on the concentration of one reactant
Rishita
September 14, 2025first order.
Deepika sheoran
September 14, 2025First order reaction is based upon the substrate concentration.
Arushi Saini
September 14, 2025first order reaction depends upon the concentration of substrate
Asha Gurzzar
September 14, 2025First order reaction
Payal Gaur
September 14, 2025Substrate concentration low then follow 1st order V directly proportional to S¹
Simran Saini
September 14, 2025First order reaction.
Pallavi Ghangas
September 14, 2025First order reaction
anjani sharma
September 14, 2025First order reaction is based on substrate concentration.
Sneha Kumawat
September 14, 2025First order reaction depend on concentration
Priyanshi sharma
September 15, 2025First order reaction because it’s depend upon substrate construction
Devika
September 15, 2025First order
Khushi Vaishnav
September 15, 2025First order reaction is based on low substrate concentration.
Yogita
September 16, 20251st order reaction
Anjana sharma
September 16, 20251st order reaction
Minal Sethi
September 16, 2025at low substrate concentration the order of reaction is first order and when the substrate concentration is high or infinite then it becomes zero order
Muskan singodiya
September 16, 20251st order reaction
Alec
September 16, 2025First order reaction because it depends on low substrate concentration
Muskan Yadav
September 17, 2025First-order kinetics because the reaction rate depends on the amount of available substrate.
Divya rani
September 17, 2025Reaction catalyzed by Enzyme at low substrate concentration is first order reaction.
Monika jangid
September 17, 20251st order reaction
Priti khandal
September 17, 2025First order