1. What is the primary function of histones in DNA packaging?
- a) Protecting DNA from damage
- b) Assisting in DNA replication
- c) Facilitating DNA packaging into nucleosomes
- d) Enhancing gene expression
Answer: c) Facilitating DNA packaging into nucleosomes
Explanation: Histones play a key role in the packing of DNA by binding to DNA and facilitating its coiling into nucleosomes, forming the basic unit of chromatin.
2. What is the structure of a nucleosome?
- a) A histone octamer wrapped with RNA
- b) A histone octamer wrapped with DNA
- c) A single histone protein
- d) A cluster of nucleotides
Answer: b) A histone octamer wrapped with DNA
Explanation: A nucleosome consists of an octamer of histone proteins around which DNA is wound, resembling beads on a string.
3. How many histone proteins are involved in the formation of a nucleosome core?
- a) 4
- b) 6
- c) 8
- d) 12
Answer: c) 8
Explanation: A nucleosome core consists of eight histone proteins—two copies of each of four types of histones (H2A, H2B, H3, and H4).
4. Which of the following histones is involved in linking nucleosomes together?
- a) H1
- b) H2A
- c) H3
- d) H4
Answer: a) H1
Explanation: Histone H1 binds to the DNA between nucleosomes, helping to stabilize the nucleosomal structure and compact the DNA further.
5. What is the role of the “linker DNA” in nucleosome formation?
- a) To stabilize the histone proteins
- b) To facilitate DNA replication
- c) To connect adjacent nucleosomes
- d) To initiate transcription
Answer: c) To connect adjacent nucleosomes
Explanation: Linker DNA connects adjacent nucleosomes, contributing to the formation of the chromatin fiber.
6. How does histone modification affect gene expression?
- a) By altering the nucleotide sequence of DNA
- b) By changing the DNA replication rate
- c) By influencing the accessibility of DNA to transcription factors
- d) By repairing DNA damage
Answer: c) By influencing the accessibility of DNA to transcription factors
Explanation: Histone modifications, such as acetylation and methylation, alter chromatin structure and regulate DNA accessibility, impacting gene expression.
7. Which of the following histone modifications typically promotes gene activation?
- a) Methylation of histone H3 at lysine 9
- b) Acetylation of histone H3 at lysine 27
- c) Acetylation of histone H3 at lysine 9
- d) Methylation of histone H4 at arginine 3
Answer: c) Acetylation of histone H3 at lysine 9
Explanation: Acetylation of histone proteins generally relaxes chromatin structure, promoting transcription and gene activation.
8. What is the primary consequence of histone deacetylation?
- a) DNA becomes more accessible for transcription
- b) Chromatin becomes more compact, silencing genes
- c) DNA replication speeds up
- d) Histone proteins lose their structure
Answer: b) Chromatin becomes more compact, silencing genes
Explanation: Deacetylation of histones leads to chromatin condensation, reducing DNA accessibility and silencing gene expression.
9. Which histone protein undergoes methylation to influence DNA packing and gene silencing?
- a) Histone H1
- b) Histone H2A
- c) Histone H3
- d) Histone H4
Answer: c) Histone H3
Explanation: Methylation of histone H3, particularly at lysine 9, is associated with gene silencing and the formation of heterochromatin.
10. What is the effect of histone phosphorylation on DNA packing?
- a) DNA becomes more tightly packed
- b) DNA becomes more accessible for transcription
- c) DNA replication is inhibited
- d) Histones are degraded
Answer: b) DNA becomes more accessible for transcription
Explanation: Phosphorylation of histones can lead to chromatin relaxation, allowing for transcriptional activation.
11. Which type of chromatin is associated with tightly packed histones?
- a) Euchromatin
- b) Heterochromatin
- c) Both euchromatin and heterochromatin
- d) Both are equally packed
Answer: b) Heterochromatin
Explanation: Heterochromatin is tightly packed, often associated with gene silencing, while euchromatin is more loosely packed and actively transcribed.
12. What happens when histones are acetylated?
- a) Chromatin becomes more compact
- b) Chromatin becomes less compact, allowing transcription
- c) Transcription factors are inhibited
- d) DNA replication is slowed
Answer: b) Chromatin becomes less compact, allowing transcription
Explanation: Acetylation neutralizes the positive charge on histones, reducing their interaction with DNA and making the chromatin more accessible to transcription machinery.
13. Histone modifications are mainly involved in regulating what biological process?
- a) DNA replication
- b) Protein synthesis
- c) Gene expression
- d) Cell division
Answer: c) Gene expression
Explanation: Histone modifications, including acetylation, methylation, and phosphorylation, regulate the structure of chromatin and thus control gene expression.
14. Which of the following best describes the effect of histone methylation at lysine 27 of H3?
- a) Gene activation
- b) Gene repression
- c) DNA replication
- d) Chromatin relaxation
Answer: b) Gene repression
Explanation: Methylation at lysine 27 of histone H3 is associated with gene repression and the formation of heterochromatin.
15. What is a key feature of “euchromatin”?
- a) It is tightly packed and inactive
- b) It is loosely packed and transcriptionally active
- c) It is involved in DNA repair
- d) It is composed of RNA
Answer: b) It is loosely packed and transcriptionally active
Explanation: Euchromatin is less condensed, allowing access to DNA for transcription, making it transcriptionally active.
16. Which histone is associated with the “beads-on-a-string” structure?
- a) H1
- b) H2A
- c) H3
- d) H4
Answer: a) H1
Explanation: Histone H1 binds to the linker DNA and helps organize the “beads-on-a-string” structure of nucleosomes.
17. What is the role of histone H3 in chromatin structure?
- a) It stabilizes DNA replication
- b) It forms part of the nucleosome core
- c) It is involved in RNA transcription
- d) It binds to the nuclear envelope
Answer: b) It forms part of the nucleosome core
Explanation: Histone H3 is one of the core histones in nucleosomes, contributing to the structural organization of chromatin.
18. How do histone modifications contribute to cellular differentiation?
- a) By regulating the expression of differentiation-related genes
- b) By altering the genetic code
- c) By promoting rapid cell division
- d) By increasing gene mutation rates
Answer: a) By regulating the expression of differentiation-related genes
Explanation: Histone modifications can activate or silence specific genes, playing a crucial role in cellular differentiation and development.
19. What is the effect of histone acetylation on chromatin structure?
- a) Chromatin becomes more condensed
- b) Chromatin becomes less condensed
- c) It prevents DNA replication
- d) It causes DNA damage
Answer: b) Chromatin becomes less condensed
Explanation: Acetylation reduces the positive charge of histones, loosening the interaction between histones and DNA, leading to a more open chromatin structure.
20. Which of the following histones is found in the nucleosome core?
- a) H1
- b) H2A
- c) H3
- d) All of the above
Answer: d) All of the above
Explanation: The nucleosome core contains two copies each of histones H2A, H2B, H3, and H4.
21. Histone proteins are predominantly rich in which amino acid residues?
- a) Serine
- b) Lysine and arginine
- c) Glutamine and asparagine
- d) Tyrosine and phenylalanine
Answer: b) Lysine and arginine
Explanation: Histone proteins are rich in positively charged amino acids, particularly lysine and arginine, which help in binding to the negatively charged DNA.
22. Which enzyme is responsible for adding acetyl groups to histones?
- a) Histone deacetylase
- b) Histone acetyltransferase
- c) DNA polymerase
- d) RNA polymerase
Answer: b) Histone acetyltransferase
Explanation: Histone acetyltransferases (HATs) add acetyl groups to histones, leading to chromatin relaxation and gene activation.
23. Which of the following processes involves histones during DNA replication?
- a) DNA unwinding
- b) DNA condensation
- c) DNA polymerization
- d) Nucleosome assembly
Answer: d) Nucleosome assembly
Explanation: After DNA replication, histones help reassemble nucleosomes onto the newly synthesized DNA strands.
24. What is the effect of histone methylation at H3K4?
- a) Gene silencing
- b) Gene activation
- c) Chromatin condensation
- d) DNA replication inhibition
Answer: b) Gene activation
Explanation: Methylation of histone H3 at lysine 4 (H3K4) is associated with transcriptionally active regions of chromatin.
25. What is the role of histone proteins in chromatin structure?
- a) DNA transcription
- b) DNA replication
- c) DNA packaging into chromatin
- d) RNA splicing
Answer: c) DNA packaging into chromatin
Explanation: Histone proteins help package DNA into nucleosomes, which further condense into chromatin, enabling DNA to fit inside the nucleus.
26. Which of the following best describes heterochromatin?
- a) Transcriptionally active
- b) Condensed and transcriptionally silent
- c) Associated with RNA splicing
- d) Replicated during mitosis only
Answer: b) Condensed and transcriptionally silent
Explanation: Heterochromatin is tightly packed and generally transcriptionally inactive, playing a role in gene silencing.
27. What is the function of histone H2A in DNA packing?
- a) It helps form the nucleosome core
- b) It stabilizes the linker DNA
- c) It assists in DNA replication
- d) It is involved in gene activation
Answer: a) It helps form the nucleosome core
Explanation: Histone H2A is a core histone that, along with other histones, forms the nucleosome core and aids in DNA packaging.
28. How does histone modification affect chromatin structure?
- a) It alters the nucleotide sequence of DNA
- b) It determines the condensation level of chromatin
- c) It directly influences DNA replication
- d) It initiates protein synthesis
Answer: b) It determines the condensation level of chromatin
Explanation: Histone modifications influence the structure of chromatin by altering its condensation level, affecting gene expression.
29. What is the role of the histone H1 protein?
- a) DNA replication
- b) Linker DNA stabilization
- c) Gene expression regulation
- d) Chromosome segregation
Answer: b) Linker DNA stabilization
Explanation: Histone H1 binds to the linker DNA between nucleosomes and helps further compact the chromatin structure.
30. Which of the following histone modifications is commonly associated with DNA repair?
- a) Methylation
- b) Acetylation
- c) Phosphorylation
- d) Ubiquitination
Answer: c) Phosphorylation
Explanation: Phosphorylation of histones is often associated with DNA damage response and repair processes.
