Questions and Answers
What term describes the regulation of when and how often a gene sequence is copied into RNA?
Which modification can silence genes by preventing them from being transcribed?
What enzyme is responsible for the methylation of DNA?
Which type of methylation ensures new DNA strands are identical to the old ones during replication?
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Which histone modification promotes transcription by neutralizing positive charges on histones?
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What is one effect of histone modifications on gene expression?
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What type of histone modification adds phosphate groups to histone proteins?
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Which of the following is NOT a type of post-translational modification of histone proteins?
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What is the effect of acetylation on histone proteins?
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What is the primary result of tri-methylation of histone H3 at lysine 27?
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Which amino acids are typically involved in the methylation of histone proteins?
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How does phosphorylation of histone proteins affect chromatin structure?
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What is the role of protein kinase in histone modification?
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What effect does ubiquitination of H2A typically have on gene expression?
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Which residues are affected by citrullination of histone proteins?
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What is a likely effect of H2B ubiquitination?
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Study Notes
Transcriptional Control
- Transcriptional control defines the timing and frequency of gene sequence copying into RNA.
- Structural-chemical modifications of genetic material play a crucial role in regulating gene expression.
- DNA binding proteins are essential for modulating gene expression by turning transcription on or off.
DNA Modification: Methylation
- In eukaryotes, cytosine bases in DNA can be converted to 5-methylcytosine through methylation by DNA methyltransferases.
- Methylation of cytosines in CpG motifs silences genes by preventing the transcription machinery from accessing the DNA.
- Two types of methylation:
- Maintenance methylation ensures newly synthesized DNA strands match the original strands during replication.
- De novo methylation involves adding methyl groups to entirely new positions on the DNA.
Histone Modifications
- Histone modifications are covalent post-translational modifications (PTMs) that include:
- Acetylation
- Methylation
- Phosphorylation
- Ubiquitination
- These modifications influence gene expression by altering chromatin structure and recruiting associated proteins.
Histone Acetylation
- Acetylation introduces negatively charged acetyl groups to lysine residues on histone proteins, promoting transcription.
- Reduced affinity of acetylated histones for DNA destabilizes chromatin, allowing gene expression to occur.
- Active genes are typically associated with acetylated histones, while unacetylated histones are found in heterochromatin.
Histone Methylation
- Generally represses transcription but can activate it when specific residues are methylated.
- Occurs mainly on lysine and arginine residues in histones H3 and H4, conducted by Histone Methyltransferases (HMTs).
- Tri-methylation of H3K27 (H3K27me3) silences gene expression, while tri-methylation of H3K4 (H3K4me3) activates transcription.
Histone Phosphorylation
- Phosphorylation occurs on serine, threonine, or tyrosine residues, conferring a negative charge to histones.
- Increased negative charge leads to a more open chromatin structure by reducing histone-DNA interactions.
- Protein kinases add phosphate groups; protein phosphatases remove them.
Histone Ubiquitination
- Involves adding ubiquitin to lysine residues at the C-terminal regions of histones H2A and H2B.
- Ubiquitination typically represses gene expression (e.g., H2A) but can also activate genes (e.g., H2B).
Citrullination of Histone Proteins
- Citrullination occurs in the N-terminal regions of histones H3 and H4, playing a role in gene regulation.
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Description
Explore transcriptional control and how gene expression is regulated in this quiz. Learn about structural-chemical modifications of genetic material, including DNA and histone proteins, and the role of DNA binding proteins. Delve into key concepts like DNA methylation and its impact on gene activity.
