Regulation of Gene Expression MCQs

Explanation: The anticodon is a sequence of three nucleotides in tRNA that is complementary to a specific mRNA codon. This sequence allows the tRNA to recognize and bind to the corresponding codon on mRNA during translation, ensuring that the correct amino acid is added to the growing polypeptide chain. The anticodon is what primarily determines the tRNA's binding specificity to mRNA.

Ans. is 'a' i.e., Valine for glutamate [Ref Harper's 29th/e p. 444] Sickle cell disease, is caused by mutation of a single base out of the 3 x 109 in the genome, a T-to-A DNA substitution, which in turn results in an A-to-U change in the mRNA corresponding to the sixth codon of the 13-globin gene. The altered codon specifies a different amino acid (valine rather than glutamic acid), and this causes a structural abnormality of the p-globin molecule.

Chondrodysplasias are a mixed group of hereditary disorders affecting cartilage. They are manifested by short-limbed dwarfism and numerous skeletal deformities. A number of them are due to a variety of mutations in the COL2A1 gene, leading to abnormal forms of type II collagen. One example is Stickler syndrome (may also be due to mutations in the COL11A1, COL11A2), manifested by degeneration of the joint cartilage and of the vitreous body of the eye. Reference: Harper's Illustrated Biochemistry, 32 nd Edition, Page Number-643.

Ans. is 'b' i.e., Translation Shine dalgarno sequence in prokaryotes and Kozak consensus sequences in eukaryotes helps in initiation of protein synthesis (Translation) In prokaryotes, a sequence of nucleotide bases on mRNA known as Shine-Dalgarno sequence (SD sequence) facilitates the binding of mRNA to the preinitiation complex. SD sequence is a purine-rich sequence of nucleotide bases, which is located -6 to -10 bp from AUG codon°. In Eukaryotes, 'Kozak consensus' sequence surrounds AUG (initiation codon) and determines the initiating codon of mRNA.

Option A: The expression of some genes is constitutive, meaning that they are expressed at a reasonably constant rate. Option B: A constitutive gene expression is not known to be subject to regulation. Option C: A constitutive gene is often referred to as housekeeping genes. Option D: As a result of mutation, some inducible gene products become constitutively expressed. A mutation resulting in constitutive expression of what was formerly a regulated gene is called a constitutive mutation. Reference: Harper's illustrated biochemistry 32 nd edition CH 38 PN 411

Explanation: Glucose inhibits the expression of the lac operon through catabolite repression. When glucose is present in high amounts, intracellular cAMP levels fall. cAMP is necessary to activate CRP (cAMP receptor protein), which binds near the promoter and helps RNA polymerase strongly attach and transcribe the lac operon.

Explanation: Cystic fibrosis is a genetic disorder caused by mutations in the CFTR gene, leading to thick mucus production that affects the lungs and digestive system. Gene therapy has been actively explored for treating cystic fibrosis. Approaches include introducing a functional copy of the CFTR gene to correct the defect. Some clinical trials have shown promise .