This set of Molecular Endocrinology Multiple Choice Questions & Answers (MCQs) focuses on “Receptor Regulation of Gene Transcription”.
1. Which among the following is a coactivator of nuclear receptor?
a) Swi/Snf complex
b) NCoR
c) SMRT
d) CGT
View Answer
Explanation: Ligands attract a set of proteins to the nuclear receptor LBD, collectively called coregulators. Coactivators are considered positively-acting coregulators. In molecular biology, SWI/SNF, which is present in eukaryotes, is a subfamily of ATP-dependent chromatin remodeling complexes.
2. What are the peptide regions of the coactivator molecules called?
a) P boxes
b) NR boxes
c) A box
d) HR boxes
View Answer
Explanation: H12 forms a hydrophobic cleft along with H3, H4, and H5 that is connected by short polypeptide regions of the coactivator molecules. There are characteristic sequences of LxxLL in these polypeptides called NR boxes, in which L is leucine and xx may be any two amino acids.
3. Which among the following is the best understood class of coactivator molecule?
a) Swi/Snf complex
b) Histone acetyltransferase
c) p160 family
d) p300/CBP
View Answer
Explanation: The p160 family, whose name is based on its protein size, is the best-known class of coactivator proteins. At least three such molecules are included in the family, and each has many names.
4. The receptor that is ligand bound enhances the transcription of the target gene to which it is bound.
a) True
b) False
View Answer
Explanation: By influencing the three-dimensional shape orientation, the ligand binding to a receptor protein changes the conformation. Ligand-dependent activation is the best understood function of nuclear receptors and their ligands. The ligand bound receptor increases transcription of a target gene to which it is bound.
5. Coactivators improve the rate of transcription of genes.
a) True
b) False
View Answer
Explanation: Co-activators are molecules that bind to an activator molecule that helps in the enhanced action of the activator. The gene transcription rate is improved by coactivators. Enzymatic functions, including DNA unwinding in response to the operation of histone acetyltransferase (HAT), accomplish this task.
6. Where the thyroid hormone receptor associated protein (TRAP) complex and the vitamin D receptor interacting protein (DRIP) complex link nuclear receptors to?
a) X factor
b) General Transcription Factors (GTFs)
c) HRE
d) mRNA
View Answer
Explanation: Some HATs also connect directly with GTFs and boost their operations more. The protein-associated thyroid hormone receptor (TRAP) complex and the protein interacting with the vitamin D receptor (DRIP) complex connect nuclear receptors to GTFs.
7. What is the role of unliganded DNA-bound nuclear receptor?
a) Active repression
b) Passive repression
c) Voltage gated repression
d) ATPase repression
View Answer
Explanation: The unliganded, DNA-bound receptor does not wait passively for the hormone, instead, the transcription of the target gene is actively repressed. This suppression shuts the target gene off and amplifies the hormone or ligand intensity of the resulting activation.
8. Which among the following is a major corepressor of nuclear receptors?
a) Chromatin remodeling
b) Swi/Snf complex
c) pCAF (p300/CBP-associated factor)
d) SMRT
View Answer
Explanation: The unliganded nuclear receptor recruits coregulators, or corepressors, to the target gene, which function negatively. Large proteins (approximately 270 kd) are the two primary corepressors: the nuclear receptor corepressor (NCoR) and the silencing mediator for retinoid and thyroid receptors (SMRT).
9. What is the name of the peptide responsible for receptor binding of corepressors?
a) CoRNR box
b) NR box
c) P box
d) PR box
View Answer
Explanation: The peptide responsible for receptor binding is called the CoRNR box in the case of corepressors. This includes the (I or L) xx (I or V) I series in which I is isoleucine, L is leucine, V is valine, and any two amino acids are represented by xx.
10. Which among the following helices does not promote or even hinders corepressor binding?
a) H3
b) H12
c) H5
d) H4
View Answer
Explanation: To form the hydrophobic pocket, the receptor uses helices 3 to 5, as in coactivator binding. However, H12 does not facilitate the binding of corepressors but it doesn’t block that too. Ligand binding is thought to reposition H12 in the case of the retinoid acid receptor and thyroid hormone receptor, inducing corepressor dissociation and coactivator recruitment, leading to transcriptional activation.
11. Which enzyme is secreted by the corepressors?
a) Histone deacetylases
b) Aromatases
c) Methylases
d) Lyases
View Answer
Explanation: The NCoR and SMRT transcriptional functions are the reverse of those of the coactivators. The corepressors themselves do not exhibit enzyme activity but do recruit histone deacetylases (HDACs) to the target gene.
12. Which Histone deacetylases acts in mammalian genome system of corepression?
a) HDAC3
b) HDAC4
c) HDAC2
d) HDAC7
View Answer
Explanation: While there are several HDACs in the mammalian genome, some of which can play a role in the function of the nuclear receptor, the key one involved in repression is HDAC3. This behavior of the enzyme relies on contact with NCoR or SMRT.
13. What is referred to as ligand-dependent negative regulation of transcription?
a) Turning off of gene targets
b) Turning off of ligands
c) Turning off of receptors
d) Turning off of DNAs
View Answer
Explanation: In the presence of the ligand, some major gene targets of hormones are switched off. To differentiate it from the suppression of basal transcription by unliganded receptors, this is referred to as ligand-dependent negative regulation of transcription, or trans repression.
14. Which is the most variable region among all members of the superfamily in terms of length and amino acid sequence?
a) A/B
b) C/D
c) B/C
d) A/D
View Answer
Explanation: In terms of length and amino acid sequence, the amino-terminal A/B domain of the nuclear receptors is the most variable region among all the members of the superfamily. Subtypes of the same receptor also have A/B domains that are entirely different.
15. What is the positive transcriptional activity of the A/B domain referred as?
a) Activation function 1 (AF-1)
b) Activation function 2 (AF-2)
c) Activation function 3 (AF-3)
d) Activation function 4 (AF-4)
View Answer
Explanation: The A/B domain contains positive transcriptional activity in several receptors, which is referred to as activation function 1 (AF-1). It is independent of the ligand, but potentially interacts with coactivators and can affect the degree of agonist or partial agonist activation.
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