Podcast
Questions and Answers
What is the primary role of histones in DNA organization?
What is the primary role of histones in DNA organization?
Which histones combine to form the octamer structure?
Which histones combine to form the octamer structure?
What is the width of the nucleofilament structure?
What is the width of the nucleofilament structure?
Which statement about euchromatin is true?
Which statement about euchromatin is true?
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What type of chemical modification can affect the stability of nucleosomes?
What type of chemical modification can affect the stability of nucleosomes?
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What structure refers to the portion of DNA between two neighboring nucleosomes?
What structure refers to the portion of DNA between two neighboring nucleosomes?
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Which histone is considered most species specific and organ specific?
Which histone is considered most species specific and organ specific?
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After DNA replication, how are the octamers distributed to the daughter DNAs?
After DNA replication, how are the octamers distributed to the daughter DNAs?
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Which of the following is a characteristic of heterochromatin?
Which of the following is a characteristic of heterochromatin?
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What is the diameter of the DNA helix?
What is the diameter of the DNA helix?
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What is the purpose of the methylation of the parental strand during DNA replication?
What is the purpose of the methylation of the parental strand during DNA replication?
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In the context of the mismatch repair system, what role does the MSH-2 gene play?
In the context of the mismatch repair system, what role does the MSH-2 gene play?
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What is the consequence of a defect in the MSH-2 gene?
What is the consequence of a defect in the MSH-2 gene?
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During the process of mismatch repair, which enzyme is primarily responsible for elongating the new DNA strand?
During the process of mismatch repair, which enzyme is primarily responsible for elongating the new DNA strand?
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What is typically found at A.P. sites in the context of Base Excision Repair?
What is typically found at A.P. sites in the context of Base Excision Repair?
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Which enzyme is responsible for detecting and removing aberrant bases during Base Excision Repair?
Which enzyme is responsible for detecting and removing aberrant bases during Base Excision Repair?
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What specific type of damage can cause deamination of cytosine, leading to its conversion to uracil?
What specific type of damage can cause deamination of cytosine, leading to its conversion to uracil?
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What sequence of events follows the identification of a mismatch by the mismatch repair system?
What sequence of events follows the identification of a mismatch by the mismatch repair system?
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In which phase of the cell cycle does the mismatch repair system primarily function?
In which phase of the cell cycle does the mismatch repair system primarily function?
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What is the primary function of DNA ligase in the mismatch repair process?
What is the primary function of DNA ligase in the mismatch repair process?
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Study Notes
DNA Organization
- Histones are positively charged proteins used to package negatively charged DNA.
- Histones are rich in positively charged amino acids (Lysine and Arginine), and also contain Mg2+.
- Types of Histones: H1, H2A, H2B, H3, and H4.
- Two units each of H2A, H2B, H3, and H4 histones aggregate to form an octamer structure (containing 8 units total).
DNA Packaging
- DNA double helix wraps around each histone octamer twice.
- It then moves to the next octamer.
- Each octamer with its wrapped DNA is called a Nucleosome.
- The portion of DNA between two nucleosomes is called Linker DNA.
- Linker DNA is associated with H1 histones.
- H3 histones are species and organ specific.
- The structure resembling a string of beads is called a Nucleofibril.
- Nucleofibril diameter is 10 nm.
- DNA helix itself is 2 nm wide.
- Nucleofibril is wrapped around a cylindrical protein called Nucleoplasmin.
- Multiple wraps of nucleofibril around nucleoplasmin form a long coil.
- This coil structure is 30 nm wide and is called the Nucleofilament.
- Nucleofilament is wrapped around a scaffolding protein.
- Open DNA double helix is called Euchromatin.
- Highly condensed portions of DNA are called Heterochromatin.
DNA Modification
- Euchromatin contains genes that are actively being transcribed (expressed).
- Nucleosomes contain 8 histone molecules and 8 amino ends of polypeptide chains protruding outwards.
- Chemical modifications of these amino ends (e.g. methylation, phosphorylation, acetylation, covalent linkage, ADP ribosylation) affect nucleosome stability.
DNA Replication and Octamer Formation
- After DNA replication, each daughter DNA strand receives one parental octamer
- The daughter DNA strand must produce its own octamers.
DNA Repair: Mismatch Repair
- DNA usually has a GATC sequence where adenine is methylated.
- After replication, one strand is methylated (parental strand) while the other is not (new strand).
- DNA mismatch repair system scans newly formed DNA double helix for mismatches in nucleotide pairs.
- If a mismatch is found, the system determines which strand is the newly formed strand and corrects the error in the new strand.
- Methylation of the parental strand serves as the marker.
- DNA segments between the two nearest GATC sites are cut and removed.
- DNA polymerase resynthesizes the DNA segment.
DNA Repair: Base Excision Repair
- DNA repair system using this method
- Purines (adenine and guanine) tend to spontaneously fall out of place.
- Nitrates and nitrites cause cytosine to deaminate and change to uracil.
- Glycosylase enzyme removes the incorrect base, creating an AP (apurinic/apyrimidinic) site.
DNA Repair: other System
- DNA polymerase joins fragments of the DNA using the 5' to 3' direction.
- Damage in the MSH-2 gene causes Hereditary Non-Polyposis Colon Cancer.
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Description
Explore the fascinating world of DNA organization and packaging in this quiz. Dive into the roles of histones, nucleosomes, and linker DNA, and understand how DNA is structured within the cell nucleus. This quiz covers essential concepts necessary for understanding molecular biology.
