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Methylation is a chemical reaction that involves the addition of a methyl group (CH3) to chemical compounds.
- Methyl Group is a small molecule that gets added to DNA, proteins, or other molecules in Methylation.
- Methylation also involves substitution of a functional group with a methyl group.
- It is considered to be a specific type of alkylation in which only a CH3 group is transferred.
- The changes to the methylation patterns of genes or proteins can affect the person’s risk of developing cancer.
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Key Terms: Methylation, Electrophilic Methylation, Methyl Group, Eschweiler-Clarke Reaction, Alkylation, Nucleophilic Methylation
What is Methylation?
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Methylation is a specific type of alkylation in which only a CH3 group is transferred and a methyl group is replaced by a hydrogen atom. In case of biological terms, methylation is catalysed by enzymes that involves regulation of proteins, and RNA processing.
- Methylation is the addition of a methyl group (CH3) to chemical compounds in Organic Chemistry.
- It involves the substitution of a functional group with a methyl group.
- The most common examples of methylation include DNA Methylation and Gene Regulation.
- The removal of methyl group from a compound is known as Demethylation.
Methylation
Read More:
| Relevant Concepts | ||
|---|---|---|
| Methane | Histones | Hofmann Elimination |
| Cytosine | Restriction Enzymes | Uses of Methanol and Ethanol |
Electrophilic Methylation
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In Electrophilic Methylation, an electrophile is the source of the methyl group. Some examples of electrophilic methylating agents are dimethyl sulphate, iodomethane, dimethyl carbonate, and diazomethane. Methylation proceeds through a SN2 reaction in Electrophilic Methylation.
Here are some examples of chemical reactions that can be classified as electrophilic methylation reactions:
- Methylation of a carboxylate ion at its oxygen to afford a methyl ester.
- Methylation of the enolate of a ketone to obtain a new ketone.
- Formation of an ether from the methylation of alkoxide ion.
- Purdie methylation reaction in which the oxygen that belongs to some carbohydrate is methylated with the help of silver oxide and iodomethane.
Nucleophilic Methylation
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Nucleophilic Methylation is the process in which a nucleophilic methylating agent is used for the transfer of a CH3 group.
Following are the examples for nucleophilic methylating agents:
- Methyllithium (CH3Li)
- Tetramethyltin ((CH3)4Sn)
- Trimethyl aluminium (Al2(CH3)6)
- Dimethyl zinc (Zn(CH3)2)
- Grignard Reagents (In which R group is a Methyl Group)
Eschweiler-Clarke Reaction
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Eschweiler-Clarke Reaction is a chemical reaction which involves methylation of a primary or secondary amine after treatment with excessive formaldehyde and formic acid. It is a method that avoids risk of quaternization, which occurs when amines are methylated with methyl halides.
Eschweiler – Clarke Reaction
What is DNA Methylation?
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DNA Methylation is defined as an inherent mechanism of gene suppression in several biological organisms.
- DNA is a sequence of base pairs that undergo transcription and translation to express them into proteins.
- But, there are some cases in which a gene shouldn’t be transcribed to mRNA as they are most likely to harm other biological processes.
- Thus, a methyl group is added to one of the bases present in the gene with the action of methyltransferase.
- That particular gene can no longer take part in transcription and hence cannot be expressed.
- This entire process is referred to as Gene Repression.
Things to Remember
- Methylation is a process that involves the addition of a methyl group (CH3) to chemical compounds.
- It can also be defined as a process that involves the substitution of a functional group with a methyl group.
- It is a type of alkylation in which only a CH3 group is transferred.
- Electrophilic Methylation and Nucleophilic Methylation are the two types of Methylation in Organic Chemistry.
- The source of the methyl group is an electrophile in electrophilic methylation.
- The source of a methyl group is a nucleophile in nucleophilic methylation.
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Previous Year Questions
- Chief use of methylated spirit is…
- Zerevitinov’s determination of active hydrogen in a… (NEET - 1994)
- Which of the following is an optically active compound… (NEET - 1989)
- Following is the substitution reaction in which… (KCET - 2011)
- What are the starting materials to get 2-methylpropene… (KEAM)
- The order of reactivity of various alkyl halides towards nucleophilic…
- When alkyl halides are heated with dry… (AIIMS - 1994)
- The ease of dehydrohalogenation of alkyl halide with… (WBJEE - 2011)
- Tertiary alkyl halide cannot be used in the Williamsons…
- Boiling points of the hydrogen halides…
Sample Questions
Ques. What is Methylation? (3 Marks)
Ans. Methylation is a chemical reaction in Organic Chemistry that is used to refer to the addition of a methyl group to a given reactant.
- Methylation can also be defined as the substitution of one of the functional groups on a given reactant with a methyl group.
- It is a type of alkylation in which a methyl group is interchanged with a hydrogen atom on a substrate.
Ques. What is Electrophilic Methylation? (3 Marks)
Ans. Electrophilic Methylation is defined as a class or type of methylation reactions in which the methyl group sources are electrophilic in nature. Here are some common examples of electrophilic methyl sources:
- Dimethyl Sulfate
- Iodomethane
- Dimethyl Carbonate
- Diazomethane
These reagents participate in methylation through SN2 reactions which are a class of nucleophilic substitution reactions.
Ques. What is Methanogenesis? (3 Marks)
Ans. Methanogenesis is defined as the formation of methane coupled to energy conservation by microbes known as methanogens.
- It is also known as ‘Biomethanation’.
- Production of methane is an important form of microbial metabolism.
- It is the final step in the decomposition of biomass in anoxic environments.
- Methanogenesis is also responsible for significant amounts of natural gas accumulations.
Ques. Explain the role of Methylation in Biological Systems? (2 Marks)
Ans. Methylation is an important reaction that is frequently used in the regulation of gene expression and the regulation of protein function in several biological systems. It should be noted that the methylation that occurs in the bodies of living things are catalysed by enzymes. Methylation also plays an important role in RNA processing in biological systems.
Ques. What is Methyltransferase? (2 Marks)
Ans. Methyltransferases are a large group of enzymes that all catalyse the addition of methyl groups to a substrate. They can be split into several subclasses based on their structural features.These enzymes play a vital role in methylating bio substrates and regulate various biological processes. They may help to enable clean and green alkylation of amino and hydroxy groups as well as reactive carbon atoms in future
Ques. What are Methanogens? (2 Marks)
Ans. Methanogens are a group of methane-producing anaerobic bacteria. These are the bacteria found in cattle dung (gobar) and in anaerobic sludge during sewage treatment. Methanogens with the help of anaerobic digestion of cellulosic plant part produces methane, carbon dioxide and hydrogen gas.
Ques. What is Eschweiler-Clarke Methylation Reaction? (2 Marks)
Ans. Eschweiler-Clarke Methylation is a reaction in which amines are subjected to methylation. The advantage of such reaction is that it avoids the chance for quaternization. The name of the reaction is derived form British and German chemist Hans Thacher Clarke and Wilhelm Eschweiler.
Ques. How are the enzymes categorized in Methyltransferase? (3 Marks)
Ans. The enzymes can be categorized into the following:
- Histone Methyltransferases
- N-terminal Methyltransferases
- DNA/RNA Methyltransferases
- Natural Product Methyltransferases
- Radical Methyltransferases
- Non-SAM dependent Methyltransferases
Ques. What is the difference between Methylation and Demethylation? (1 Mark)
Ans. Methylation is a chemical reaction that involves the functional group with a methyl group whereas the removal of methyl group from a compound is known as demethylation.
Ques. Which all gases are produced during sewage treatment? (2 Marks)
Ans. The gases which are produced during the sewage treatment are:
- Methane (CH4)
- Hydrogen sulfide (H2S)
- Carbon-dioxide (CO2)
Ques. How is Biogas produced? (3 Marks)
Ans. Biogas is the mixture of gases that consists of primarily methane and carbon dioxide that is produced by the breakdown of organic substance into such gases in the lack of oxygen.
- Biogas is produced when bacteria digest organic matter in oxygen absence.
- It is referred to as anaerobic digestion.
- It occurs naturally within the digestive system to the depth of effluent ponds.
- It can be reproduced artificially in engineered containers called digesters.
Ques. Which bacterias are responsible for converting organic acids into Methane? (1 Mark)
Ans. The bacterias which are responsible for converting organic acids into Methane are:
- Anaerobic Bacteria
- Methanogenic Bacteria
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