(DEC 2004)
76. The best example of regulation of enzyme by reversible covalent modification is-
(1) Phosphorylation (2) Acetylation
(3) Glycosylation (4) proteolytic cleavage
The correct answer is (1) Phosphorylation.
Introduction
Cellular enzyme regulation is critical for maintaining metabolic balance and responding to environmental changes. One of the most effective and widespread means of regulating enzyme activity is through reversible covalent modification, where chemical groups are added to or removed from enzymes to modulate their function dynamically. Among various types—phosphorylation, acetylation, glycosylation, and proteolytic cleavage—phosphorylation stands out as the best and most studied example of reversible covalent enzyme regulation.
Reversible Covalent Modification Explained
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Definition: Addition and removal of chemical groups via covalent bonds that can be reversed, allowing dynamic control of enzyme function.
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Modifications typically target side chains of amino acids such as serine, threonine, or tyrosine.
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The reversible nature enables enzymes to switch between active and inactive states rapidly in response to physiological signals.
Why Phosphorylation Is the Best Example
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Mechanism: A phosphate group is added to hydroxyl groups of serine, threonine, or tyrosine residues by protein kinases and removed by phosphatases.
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Regulatory flexibility: Phosphorylation can either activate or inhibit enzyme activity, alter protein-protein interactions, and change enzyme localization.
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Prevalence: Involved in virtually all cellular processes including cell cycle control, metabolism, and signal transduction.
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Fast and reversible: Provides rapid response adjustment to cellular needs.
Comparison with Other Modifications
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Acetylation: Also reversible but mostly modifies histones or transcription factors, less common for direct enzyme activity regulation.
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Glycosylation: Generally irreversible modification affecting protein folding and stability rather than rapid enzymatic regulation.
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Proteolytic cleavage: Irreversible; permanently activates or inactivates enzymes by peptide bond hydrolysis.
Key Examples of Phosphorylation in Enzyme Regulation
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Glycogen phosphorylase: Activated by phosphorylation to mobilize glucose.
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Pyruvate dehydrogenase: Activity modulated by phosphorylation state coordinating metabolism.
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MAP kinase pathways: Phosphorylation cascades that relay extracellular signals inside the cell.
Summary Table
| Modification Type | Reversibility | Functional Role | Example |
|---|---|---|---|
| Phosphorylation | Reversible | Dynamic enzyme control | Glycogen phosphorylase |
| Acetylation | Reversible | Mostly gene regulation | Histone proteins |
| Glycosylation | Usually irreversible | Protein stability | Cell surface receptors |
| Proteolytic cleavage | Irreversible | Enzyme activation | Digestive enzymes (trypsin) |
Conclusion
Phosphorylation is the best-illustrated example of reversible covalent enzyme regulation due to its dynamic, widespread impact on enzyme function and cellular metabolism. Its reversible nature and prompt responsiveness make it indispensable for biological regulation, far surpassing other modifications like acetylation or proteolytic cleavage.
54 Comments
yashika
September 12, 2025Phosphorylation is best example of reversible covalent enzyme regulation
Vijay Marmat
September 12, 2025Phosphorylation correct ✔️
reversible covalent enzyme regulation
Mahima Sharma
September 16, 2025Phosphorylation
Kirti Agarwal
September 12, 2025Phosphorylation is best for direct enzyme regulation
Khushi Vaishnav
September 12, 2025Phosphorylation is best example of regulation of enzyme by reversible covalent modification
Sakshi yadav
September 12, 2025Phosphorylation is best eg for regulation of enzyme by reversible covalent
anjani sharma
September 12, 2025Phosphorylation is best example of reversible covalent enzyme regulation.
So answer a
Mahima Sharma
September 14, 2025Phosphorylation is best for reversible covalent enzyme regulaton
Neelam Sharma
September 12, 2025Enzyme regulations k ley two facty depend krte h 1st allosteric enzyme reversible regulation and 2 nd is modification of enzyme covalent yh irreversible or reversible dono hota h but fastly or reversible regulation best enzyme regulations h jisme phosphorylation is best reversible covalent regulation h kyunki enzyme k oH grp pr phosphate ATP davara addd hota h kinase enzyme se or remove by phosphatase so best regulation of enzyme
Varsha Tatla
September 13, 2025Enz regulations depends upon two factors one is allosteric enz reversible regulation
Nd another is modification of enz
In modification of enz phosphorilytion is best regulation type
Savita Garwa
September 13, 2025Phosphorylation is best example of reversible covalent enzyme regulation
Kajal
September 13, 2025Option A means phosphorylation is best for enzyme regulation
Konika Naval
September 13, 2025The best example of regulation of enzyme by reversible covalent modification is phosphorylation.
Kanica Sunwalka
September 13, 2025phosphorylation is best example of regulation of enzyme by reversible covalent modification
( as phosphate grp is added by protein kinases and removed by phosphatases )
Aartii sharma
September 13, 2025Phosphorylation is the best example of enzyme by reversible covalent modification
Rishita
September 13, 2025Phosphorylation
Asha Gurzzar
September 13, 2025Phosphorylation is Best answer
Aakansha sharma Sharma
September 13, 2025Phosphorylation is best example of reversible covalent enzyme regulation
Saniya Jangid
September 14, 2025Phosphorylation
Anju
September 14, 2025Ans :1 ( phosphorylation)
Activate or inhibit enzym activity
Protein- protein intraction
Protein localization
Pratibha Jain
September 14, 2025Correct answer is option (1)
phosphorylation is best example of regulation of enzyme by reversible covalent modification
( as phosphate grp is added by protein kinases and removed by phosphatases )
Santosh Saini
September 14, 2025Phosphorylation is the best example of reversible covalent enzyme regulation due to its dynamic enzymes control
Meera gurjar
September 14, 2025Phosphorylation
Payal Gaur
September 14, 2025Phosphorylation is best for regulation of enzyme ( reversible modifications ).
Pallavi Ghangas
September 14, 2025Phosphorylation is used for enzyme regulation by reversible covalent modification
Dharmpal Swami
September 14, 2025Phosphorylation is used for enzyme regulation by reversible covalent modification
Palak Sharma
September 14, 2025Phosphorylation is best example of regulation of enzyme by reversible covalent modification.
Deepika sheoran
September 14, 2025Phosphorylation is used for enzyme Regulation by reversible covalent modification..
Lokesh Kumawat
September 14, 2025Phosphorylation is best example of regulation of enzyme by reversible covalent modification.
Priya dhakad
September 14, 2025phosphorylation is best for enzyme regulation.
Divya rani
September 14, 2025Phosphorylation is The best example of reversible covalent enzyme regulation.
Sachin kant sharma
September 14, 2025Phosphorylation is best example
Sachin kant sharma
September 14, 2025Phosphorylation is best example of enzyme regulation
Sachin kant sharma
September 14, 2025Phosphorylation is best example of enzyme regulation of rev covalent
Vanshika Sharma
September 15, 2025Phosphorylation is the best example of reversible covalent enzyme regulation
Devika
September 15, 2025Phosphorylation
Parul Yadav
September 15, 2025The most effective way of enzymatic activity regulation is through REVERSIBLE COVALENT MODIFICATION – Phosphorylation is best among them.
Bhawna Choudhary
September 15, 2025Phosphorylation is correct
Mansukh Kapoor
September 15, 2025The correct answer is option 1st
Phosphorylation is best for direct enzyme regulation
Soniya Shekhawat
September 15, 2025Phosphorylation is best for regulation of enzyme ( reversible modifications ).
Anjana sharma
September 16, 2025Phosphorylation have reverse dynamic catalytic activity
Aafreen Khan
September 16, 2025Phosphorylation is the best example of regulation of an enzyme by reversible covalent because it involves the addition or removal of a phosphate group
Nilofar Khan
September 16, 2025Phosphorylation is correct answer
Mohd juber Ali
September 16, 2025Phosphorylation beat for direct enzyme regulation
Vinita Meena
September 16, 2025Phosphorylation is best eg for regulation of enzyme by reversible covalent
Payal Gaur
September 16, 2025Phosphorylation
priya khandal
September 17, 2025phosphorylation is a best example for gene regulation of enzyme
Muskan Yadav
September 17, 2025Phosphorylation
Simran Saini
September 17, 2025Phosphorylation is best example of regulation of enzyme by reversible covalent modification.
Tanvi Panwar
September 17, 2025Phosphorylation is the best example of reversible covalent modification.
Avni
September 17, 2025The correct answer is (1) Phosphorylation
Aafreen Khan
September 23, 2025Option 1st – Phosphorylation is best for regulation of enzyme reversible
Neelam Sharma
September 23, 2025Phosphorylation is best example of reversible covalent enzyme regulation
Sachin kant sharma
September 27, 2025Phosphorylation for best option in reversible covalent modification