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Which of the following is the fundamental unit of chromatin structure?
A. Chromatid
B. Nucleosome
C. Chromosome arm
D. Centromere
Answer: B. Nucleosome
Rationale: A nucleosome consists of DNA wrapped around a histone octamer and is the repeating structural unit of chromatin. -
The “linker” histone protein that helps compact nucleosome arrays is:
A. H2A
B. H3
C. H1
D. H4
Answer: C. H1
Rationale: Histone H1 binds the DNA entry/exit on the nucleosome and promotes higher-order chromatin folding. -
The region on a chromosome that attaches to spindle microtubules during mitosis is called the:
A. Telomere
B. Centromere
C. Nucleosome
D. Scaffold attachment region (SAR)
Answer: B. Centromere
Rationale: The centromere is the primary constriction and binds the kinetochore for spindle attachment. -
Chromatin that is loosely packed and transcriptionally active is called:
A. Heterochromatin
B. Euchromatin
C. Satellite DNA
D. Telomeric chromatin
Answer: B. Euchromatin
Rationale: Euchromatin is less condensed, accessible for transcription, and gene-rich. -
Domains known as “topologically associating domains (TADs)” are characterised by:
A. DNA interacting more frequently within the domain than outside it
B. Having only heterochromatic sequences
C. Being composed only in mitosis
D. Being unchanging between cell types
Answer: A. DNA interacting more frequently within the domain than outside it
Rationale: TADs are self-interacting genomic regions where chromatin interactions are enriched within the domain. (Wikipedia) -
The large-scale compartments labelled “A” and “B” in the 3D genome refer to:
A. Nucleosome positions
B. Euchromatin (A) and heterochromatin (B) compartments
C. S-phase and G2 phase genomes
D. Centromere and telomere compartments
Answer: B. Euchromatin (A) and heterochromatin (B) compartments
Rationale: The A and B compartments reflect active (A) versus inactive (B) chromatin in 3D nuclear space. (OUP Academic) -
Which protein complex is primarily involved in loop extrusion in interphase chromatin architecture?
A. DNA polymerase
B. Cohesin
C. Telomerase
D. Ribosome
Answer: B. Cohesin
Rationale: Cohesin (and condensin) are SMC-protein complexes that help extrude chromatin loops, shaping the 3D architecture. (MDPI) -
The transition from interphase chromatin to mitotic chromosomes involves:
A. Complete loss of architectural proteins
B. Retention of architectural proteins and re-folding of loops into condensed states
C. Chromatin becoming completely linear
D. All transcription ceasing permanently
Answer: B. Retention of architectural proteins and re-folding of loops into condensed states
Rationale: Architectural proteins like CTCF/cohesin are retained and help preserve “mitotic memory” of interphase structure. (PLOS) -
Telomeres are important because they:
A. Anchor chromosomes to the spindle
B. Protect chromosome ends from degradation/fusion
C. Are the sites of transcription for most genes
D. Are the only heterochromatic regions in a chromosome
Answer: B. Protect chromosome ends from degradation/fusion
Rationale: Telomeres consist of repetitive DNA that safeguards chromosome ends. -
Lamina-associated domains (LADs) are:
A. Regions of active transcription near the nuclear centre
B. Genomic regions tethered to the nuclear lamina and generally inactive
C. The binding sites for DNA polymerase
D. Only found in prokaryotes
Answer: B. Genomic regions tethered to the nuclear lamina and generally inactive
Rationale: LADs are part of the B compartment, often heterochromatic and near the nuclear periphery. (OUP Academic) -
Which level of chromatin organization corresponds to the “beads on a string” 10-nm fibre?
A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure
Answer: A. Primary structure
Rationale: The 10-nm fibre (DNA + nucleosomes) is the primary chromatin fibre before higher-order folding. -
The 30-nm chromatin fibre is considered what level of chromatin folding?
A. Primary
B. Secondary
C. Tertiary
D. Quaternary
Answer: B. Secondary
Rationale: The 30 nm fibre arises from coiling/stacking of the 10 nm fibre into a higher compact form. -
In the context of chromosome architecture, what is an “isochore”?
A. A type of histone modification
B. A large DNA segment of relatively homogeneous base composition
C. A protein complex that compacts chromatin
D. A telomeric repeat sequence
Answer: B. A large DNA segment of relatively homogeneous base composition
Rationale: Isochores correlate with chromatin architecture and banding patterns. (PLOS) -
The protein CTCF is important because it:
A. Is the major histone in nucleosomes
B. Marks boundaries of chromatin domains such as TADs
C. Synthesises DNA
D. Anchors ribosomes to the ER
Answer: B. Marks boundaries of chromatin domains such as TADs
Rationale: CTCF binding sites often delineate TAD boundaries and mediate chromatin loop anchors. (Cell) -
Which statement is true about heterochromatin?
A. Always transcriptionally active
B. Generally gene-poor and tightly packed
C. Located exclusively in the nucleus centre
D. Has no role in genome stability
Answer: B. Generally gene-poor and tightly packed
Rationale: Heterochromatin is compacted, often transcriptionally silent, and associated with structural support. -
What does the method Hi‑C measure in the context of chromosome architecture?
A. DNA methylation levels only
B. Frequency of physical contacts between genomic loci genome-wide
C. Protein translation rate
D. Telomere length
Answer: B. Frequency of physical contacts between genomic loci genome-wide
Rationale: Hi-C captures 3D chromatin interactions across the genome. (Wikipedia) -
The structural maintenance of chromosomes (SMC) complexes include Condensin and cohesin. A principal role of condensin is:
A. Loop extrusion during mitotic chromosome condensation
B. Transcription initiation
C. RNA splicing
D. Telomere extension
Answer: A. Loop extrusion during mitotic chromosome condensation
Rationale: Condensin compacts chromosomes by promoting loop formation and higher-order folding. (MDPI) -
Which of the following best describes “chromosome domain architecture and dynamic organization”?
A. Static, identical across all cell types
B. Dynamic, hierarchical, involving loops, TADs, compartments and changes during the cell cycle
C. Irrelevant for gene regulation
D. Only exists in prokaryotes
Answer: B. Dynamic, hierarchical, involving loops, TADs, compartments and changes during the cell cycle
Rationale: Chromosome architecture is hierarchical and changes with cell state and cycle. (febs.onlinelibrary.wiley.com) -
Chromatin loop anchors often include which two factors?
A. RNA polymerase II and histone H1
B. CTCF and cohesin
C. Telomerase and DNA polymerase
D. Ribosomal proteins
Answer: B. CTCF and cohesin
Rationale: These factors mediate loop formation and domain boundary formation. -
The term “mitotic memory” refers to:
A. DNA replication fidelity only
B. The concept that interphase chromatin organisation can be restored after mitosis thanks to retained architectural proteins
C. The memory of the spindle apparatus
D. Telomere shortening
Answer: B. The concept that interphase chromatin organisation can be restored after mitosis thanks to retained architectural proteins
Rationale: Architectural proteins retained in mitosis enable re-establishment of interphase architecture. (PLOS) -
Which of the following is not a feature of the 3D genome architecture in interphase?
A. Chromosome territories
B. Euchromatin and heterochromatin compartments
C. Random, completely unstructured DNA
D. Chromatin loops linking enhancers/promoters
Answer: C. Random, completely unstructured DNA
Rationale: The genome is highly structured, not random; chromosome territories and looping are key features. -
During conversion from interphase to mitotic chromosomes, chromatin:
A. Loses all loops and domain structure permanently
B. Undergoes re-folding into highly condensed structures, but many architectural features are preserved or reused
C. Becomes fully unfolded
D. Doubles in size
Answer: B. Undergoes re-folding into highly condensed structures, but many architectural features are preserved or reused
Rationale: Although compaction increases dramatically, key architectural proteins and binding sites persist. (ScienceDirect) -
In plants and animals, the 3-D genome architecture influences:
A. Only DNA replication
B. Gene expression patterns, cell-fate, genome stability
C. Only protein folding
D. None of the above
Answer: B. Gene expression patterns, cell-fate, genome stability
Rationale: Spatial genome organisation plays a key role in regulation and development. (Frontiers) -
Which of the following is true regarding chromatin packing domains and biochemical properties?
A. All chromatin has identical solubility and packing
B. Biochemical fractionation reveals active and inactive chromatin domains with distinct properties
C. Chromatin packing domains only exist in bacteria
D. They have no relation to gene regulation
Answer: B. Biochemical fractionation reveals active and inactive chromatin domains with distinct properties
Rationale: Studies show different accessibility/solubility for euchromatin vs heterochromatin domains. (OUP Academic) -
Which statement best describes the relationship between linear DNA sequence features and 3-D chromosome architecture?
A. There is no relationship.
B. Sequence composition (e.g., isochores), architectural protein binding sites, and chromatin state all contribute to 3-D architecture.
C. Only histone modifications matter, sequence is irrelevant.
D. Loop extrusion destroys all sequence-based organisation.
Answer: B. Sequence composition (e.g., isochores), architectural protein binding sites, and chromatin state all contribute to 3-D architecture.
Rationale: Research shows correlation between sequence composition, binding sites of architectural proteins and chromosome folding patterns. (PLOS)
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