This set of Molecular Biology Interview Questions and Answers for freshers focuses on “Genome Organization – 3”.
1. Which of the following facilitates nucleosome positioning?
a) Nucleosome remodeling complex
b) Topoisomerase II
c) SMC protein
d) DNA – binding protein
View Answer
Explanation: Nucleosome positioning can be directed by DNA – binding protein or particular DNA sequences. Just as many proteins cannot bind to DNA within the nucleosome, prior binding of a protein to a site on DNA can prevent association of the core histone with that stretch of DNA. If two such DNA – binding proteins are bound to sites closer than the minimal nucleosomal DNA requirement (≈150 bp) the DNA stretch between the two proteins will remain nucleosome free.
2. Which of the following regions promote histone – DNA association?
a) A, T
b) A, G
c) G, C
d) C, T
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Explanation: A:T rich DNA has an intrinsic tendency to bend toward the minor grove. Thus A:T rich DNA is favored in positions in which the minor grove faces the histone octamer. G:C rich DNA has the opposite tendency thus, is favored when the major grove faces away from the histone octamer.
3. With respect to end terminal modification of the histone tail which of the following options is true?
a) Lysine – phosphate modification
b) Serine – methylation
c) Acetylation – transcriptionally active
d) Modifications – involvement in gene expression
View Answer
Explanation: Acetylation marks transcriptionally active region whereas methylation marks both transcriptionally active and repressed regions. Finally, phosphorylation histone H3 is commonly seen in highly condensed chromatin. Thus, these modifications result in a code that can be read by the proteins involved in gene regulation and expression.
4. Which of the following is a function of a modified histone tail?
a) Association with adjacent nucleosome
b) Interaction with DNA backbone
c) Interaction with chromodomains
d) Formation of 40-fold DNA structure
View Answer
Explanation: Modification of histone tail generates binding sites for proteins. Specific protein domains called bromodomains and chromodomains mediate these interactions. Chromodomains containing proteins interact with methylated histone tails and are generally associated with tail specific methylating enzymes.
5. Bromodomains of proteins are associated with phosphorylated histone tails.
a) True
b) False
View Answer
Explanation: Bromodomains of proteins interacts with the acetylated histone tails. These proteins are generally associated with histone tail – specific acetyl transferases. Such complexes facilitate the maintenance of acetylated chromatin by further modifying the already acetylated regions.
6. Which of the following enzymes of transcription commonly contains a bromodomain?
a) TFIID
b) CDK
c) Pre – RC
d) DNA polymerase
View Answer
Explanation: Bromodomain containing proteins are involved in regulating transcription or formation of heterochromatin. Only TFIID of the above options is involved in transcription of DNA whereas the others are involved in DNA replication.
7. Which of the following enzymes is not correctly paired with its function?
a) Acetyl transferase – adds acetyl group to lysine
b) Methyl transferase – adds methyl group to serine
c) Topoisomerase – associated with nuclear scaffold
d) Deacetylases – removes acetyl groups from serine
View Answer
Explanation: Methylation is an N – terminal modification of histone tail induced by the enzyme methyl transferase. But methylation is induced in the amino acid lysine. Serine is generally involved with phosphorylation.
8. Which of the following is not promoted by histone tail modification?
a) Formation of repressive structures
b) Gene expression
c) Nucleosome remodeling
d) Nucleosome sliding
View Answer
Explanation: Nucleosome sliding is a type of Nucleosome remodeling. It is facilitated by Nucleosome remodeling complex. It cannot be promoted alone by modifying histone tail unless a nucleosome remodeling complex comes along.
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