Podcast
Questions and Answers
What aspect of histones facilitates their interaction with DNA?
What aspect of histones facilitates their interaction with DNA?
- Histones are catalyzed by enzymes to form covalent bonds with DNA.
- Histones possess a net negative charge that attracts DNA.
- Histones are rich in positively charged amino acids, allowing electrostatic interactions with negatively charged DNA. (correct)
- Histones contain both hydrophobic and hydrophilic regions for amphipathic interactions with the DNA double helix.
Which of the following statements accurately describes the composition of a histone octamer?
Which of the following statements accurately describes the composition of a histone octamer?
- Four units each of H2A and H2B histones only.
- Two units each of H1, H2A, H2B, H3, and H4 histones.
- A single unit each of H1, H2A, H2B, H3, and H4 histones.
- Two units each of H2A, H2B, H3, and H4 histones, without H1. (correct)
What is the correct order of DNA packaging, from least to most condensed?
What is the correct order of DNA packaging, from least to most condensed?
- DNA double helix, Nucleosome, Nucleofibrile, Nucleofilament (correct)
- Nucleofilament, Nucleofibrile, Nucleosome, DNA double helix
- Nucleosome, DNA double helix, Nucleofilament, Nucleofibrile
- DNA double helix, Nucleofilament, Nucleosome, Nucleofibrile
Linker DNA, situated between nucleosomes, is associated with which histone variant?
Linker DNA, situated between nucleosomes, is associated with which histone variant?
How does the function of Euchromatin differ from that of Heterochromatin?
How does the function of Euchromatin differ from that of Heterochromatin?
Which chemical modification is most directly associated with the silencing of gene expression?
Which chemical modification is most directly associated with the silencing of gene expression?
What is the functional significance of the amino ends of histone proteins protruding outward from the nucleosome?
What is the functional significance of the amino ends of histone proteins protruding outward from the nucleosome?
What is the role of Nucleoplasmin in chromatin structure?
What is the role of Nucleoplasmin in chromatin structure?
What characterizes the Barr body observed in female mammalian cells?
What characterizes the Barr body observed in female mammalian cells?
Considering the process of DNA replication, what happens to parental histones?
Considering the process of DNA replication, what happens to parental histones?
Given that methylation of DNA suppresses gene transcription, how does histone acetylation counteract this effect to regulate chromatin remodeling?
Given that methylation of DNA suppresses gene transcription, how does histone acetylation counteract this effect to regulate chromatin remodeling?
How does the wrapping of DNA around histone octamers to form nucleosomes affect DNA accessibility and gene expression?
How does the wrapping of DNA around histone octamers to form nucleosomes affect DNA accessibility and gene expression?
If a mutation occurred that prevented histones from being positively charged, what would be the most likely outcome?
If a mutation occurred that prevented histones from being positively charged, what would be the most likely outcome?
Which characteristic distinguishes H1 histones from the other histone types (H2A, H2B, H3, H4)?
Which characteristic distinguishes H1 histones from the other histone types (H2A, H2B, H3, H4)?
A cell with increased levels of heterochromatin would likely exhibit which characteristic?
A cell with increased levels of heterochromatin would likely exhibit which characteristic?
Which statement correctly relates the width of the DNA helix, nucleofibrile, and nucleofilament?
Which statement correctly relates the width of the DNA helix, nucleofibrile, and nucleofilament?
How does acetylation of histones contribute to chromatin remodeling and gene expression?
How does acetylation of histones contribute to chromatin remodeling and gene expression?
Where is H1 histone located relative to the nucleosome and what is its function?
Where is H1 histone located relative to the nucleosome and what is its function?
How does the arrangement of nucleosomes into a nucleofilament affect the accessibility of DNA for transcription?
How does the arrangement of nucleosomes into a nucleofilament affect the accessibility of DNA for transcription?
Flashcards
Histones
Histones
Positively charged proteins used to wrap negatively charged DNA polymers. Rich in lysine, arginine, and Mg2+.
Octamer
Octamer
H2A, H2B, H3, and H4 histones aggregate in two units each to form this structure.
Nucleosome
Nucleosome
The structure formed when DNA is wrapped twice around an octamer.
Linker DNA
Linker DNA
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Nucleofibril
Nucleofibril
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Nucleoplasmin
Nucleoplasmin
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Nucleofilament
Nucleofilament
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Scaffolding Protein
Scaffolding Protein
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Euchromatin
Euchromatin
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Heterochromatin
Heterochromatin
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Euchromatin function
Euchromatin function
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Methylation of DNA effect
Methylation of DNA effect
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Acetylation of histones effect
Acetylation of histones effect
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Barr body
Barr body
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Study Notes
- Histones are positively charged (cationic) proteins that wrap up negatively charged DNA polymers.
- Histones are rich in positively charged amino acids like lysine and arginine, and magnesium (Mg2+).
- The types of histones consist of H1, H2A, H2B, H3 and H4.
- Two units each of H2A, H2B, H3, and H4 histones aggregate together to form an octamer, which has eight units total.
- The DNA double helix wraps around each octamer twice, then continues to the next octamer.
- A nucleosome is each octamer with DNA wrapped around it twice.
- Linker DNA is the portion of DNA between two neighboring nucleosomes.
- Linker DNA associates with H1 histones.
- H1 histones are the most species-specific and organ-specific of all histones.
- Nucleofibril refers to a structure that looks like a chain of beads.
- The DNA helix is 2 nm wide.
- The nucleofibril is 10 nm wide.
- The nucleofibril wraps around a cylindrical-shaped protein called nucleoplasmin.
- When nucleofibril wraps around nucleoplasmin multiple times, nucleoplasmin moves out and leaves a long coil made of nucleofibril.
- This coil structure is 30 nm wide and is called nucleofilament.
- Nucleofilament wraps or coils around a long protein called a scaffolding protein.
- Euchromatin is DNA that is open and made of just a double helix.
- Heterochromatin refers to highly condensed portions of DNA.
- Euchromatin consists of portions of DNA transcribed (genes being expressed).
- Each nucleosome has eight histone molecules, and as histones are proteins, each nucleosome has eight amino ends of polypeptides protruding outwards.
- Chemical modification of these amino ends affects the stability of the nucleosome.
Chemical modifications
- Methylation
- Phosphorylation
- Acetylation
- Covalent linkage
- ADP ribosylation
- After DNA replication, all octamers from the parental DNA go to one of the daughter DNAs and the second daughter DNA has to make its own octamers.
Chromatin Remodeling Regulation
- Several ways regulate chromatin remodeling (Euchromatin <-> Heterochromatin), two of which are most widely used.
- Methylation of the DNA suppresses transcription.
- Acetylation of histones causes dissociation of bonds between histones and DNA, as a result heterochromatin changes into euchromatin.
- A classical example of heterochromatin is a Barr body.
- A Barr body is one of the female X chromosomes that is highly methylated and inactive.
- Depending on where the centromere is located, there are three types of chromosomes: acrochromosome, submetachromosome, and metachromosome.
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