17. Following is a table in which the List I contains names of various steps of gene expression and in those List II are the enzymes associated with those. Match the components of List I with those in List II.
List I                                                                                              List II
A. Epigenetic regulation                                                        I. Endonuclease
B. DNA repair                                                                            II. Histone methyltransferase
C. Transcription                                                                       III. eIF2 Kinase
D. Translation                                                                           IV. RNA polymerase
Choose the correct answer from the options given below:
Options:-
(a) A – II, B – I, C – IV, D – III,
(b) A – II, B – IV, C – I, D – III,
(c) A – III, B – II, C – IV, D – I,
(d) A – IV, B – III, C – II, D – I,

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Introduction to Gene Expression and Enzyme Functions

Gene expression is the process by which genetic information is used to synthesize proteins and RNA molecules, critical for cellular function. The regulation and execution of gene expression are tightly controlled, and various enzymes play pivotal roles in each step. From epigenetic regulation to transcription and translation, enzymes facilitate these processes, ensuring that cells function correctly.

This article will explore the different steps of gene expression and the enzymes associated with each step, helping you understand how they work together to regulate gene activity.

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Step-by-Step Breakdown of Gene Expression

Gene expression occurs through a series of tightly regulated steps:

1. Epigenetic Regulation: This refers to changes in gene expression or cellular phenotype that do not involve changes to the underlying DNA sequence. Epigenetic modifications, such as DNA methylation and histone modification, help control whether genes are turned on or off. Enzymes like histone methyltransferase are key players in modifying histones, which in turn regulates DNA accessibility.

2. DNA Repair: DNA repair mechanisms are essential for maintaining the integrity of the genome. Various enzymes, including endonucleases, are involved in recognizing and repairing damaged DNA. These enzymes cut the DNA backbone, allowing for the repair of mismatched or damaged nucleotides.

3. Transcription: Transcription is the process by which an RNA copy of a gene is made. RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template. Transcription is the first step in expressing a gene and is heavily regulated by various factors, including eIF2 Kinase, which controls the initiation of protein synthesis.

4. Translation: Translation is the process of converting the RNA sequence into a protein. This occurs in the ribosome, where transfer RNA (tRNA) matches codons of mRNA to their corresponding amino acids, forming proteins. Translation initiation is regulated by enzymes such as eIF2 Kinase, which is involved in the phosphorylation of translation initiation factors.

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Matching the Steps of Gene Expression with Enzymes

Let’s now examine the enzymes associated with each step of gene expression as outlined in the table:

• A. Epigenetic Regulation: The enzyme Histone methyltransferase (List II, II) plays a crucial role in modifying histones, thus regulating gene expression at the chromatin level. This allows for either activation or repression of specific genes.

• B. DNA Repair: The enzyme Endonuclease (List II, I) is involved in cutting the DNA backbone at specific sites, allowing for the repair of damaged or mismatched bases. Endonucleases are key in the process of excision repair.

• C. Transcription: The enzyme RNA polymerase (List II, IV) is responsible for synthesizing RNA from the DNA template during transcription. This enzyme binds to DNA and catalyzes the formation of RNA.

• D. Translation: The enzyme eIF2 Kinase (List II, III) is involved in regulating translation initiation. It plays a crucial role in controlling protein synthesis in response to various stress conditions.

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Analysis of the Options

Now, let’s match each step with its corresponding enzyme:

• Option (a) A – II, B – I, C – IV, D – III:

  • A (Epigenetic Regulation): Histone methyltransferase (II) is correctly matched.

  • B (DNA Repair): Endonuclease (I) is correctly matched.

  • C (Transcription): RNA polymerase (IV) is correctly matched.

  • D (Translation): eIF2 Kinase (III) is correctly matched.

This is the correct option.

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Conclusion

Gene expression involves a complex series of steps, each regulated by specific enzymes that facilitate or inhibit processes such as transcription, translation, and DNA repair. The correct matching of each process with its corresponding enzyme is essential for understanding the molecular mechanisms that control gene expression.

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Answer:

The correct answer is: (a) A – II, B – I, C – IV, D – III.