Textbook Question
What parts of the genome are reversibly methylated? How does this affect gene expression?
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13. Gene Regulation in Eukaryotes
Epigenetics, Chromatin Modifications, and Regulation
0:28 minutesProblem 7
Textbook Question
Provide a brief description of two different types of histone modification and how they impact transcription.
Verified step by step guidance1
Step 1: Understand that histone modifications are chemical changes to the histone proteins around which DNA is wrapped, affecting how tightly or loosely DNA is packaged and thus influencing gene expression.
Step 2: Describe acetylation as a type of histone modification where an acetyl group (−COCH₃) is added to lysine residues on histone tails, which neutralizes positive charges and reduces histone-DNA interaction, leading to a more open chromatin structure and increased transcription.
Step 3: Describe methylation as another type of histone modification where one or more methyl groups (−CH₃) are added to lysine or arginine residues on histones; depending on the specific site and degree of methylation, this can either activate or repress transcription.
Step 4: Explain that acetylation generally promotes transcription by loosening chromatin, making DNA more accessible to transcription factors and RNA polymerase, while methylation can have dual roles—either activating or repressing transcription based on the context of the modification.
Step 5: Summarize that these histone modifications are part of the epigenetic regulation mechanisms that dynamically control gene expression without altering the underlying DNA sequence.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Histone Modifications
Histone modifications are chemical changes to histone proteins around which DNA is wrapped. These modifications, such as methylation and acetylation, alter chromatin structure and influence gene accessibility, thereby regulating gene expression.
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Histone Acetylation
Histone acetylation involves adding acetyl groups to lysine residues on histone tails, neutralizing their positive charge. This reduces histone-DNA interaction, leading to a more relaxed chromatin structure that promotes transcription by allowing transcription factors easier access to DNA.
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Histone Methylation
Histone methylation adds methyl groups to specific amino acids on histones, which can either activate or repress transcription depending on the site and degree of methylation. For example, methylation of H3K4 is linked to gene activation, while H3K9 methylation is associated with gene silencing.
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