Question

The synthesis of normal adult hemoglobin (HbA) requires the coordinated synthesis \(\alpha\) -globin and \(\beta\) -globin. \(\beta\) -Thalassemia is a genetic disease leading to a deficiency of \(\beta\) -globin chains and an inability of the blood to deliver oxygen properly. \(\beta\) -Thalassernia can result from a wide variety of mutations. One mutation leading to \(\beta\) -thalassemia occurs at a splice junction. Which of the following statements about removing introns is correct? A. Small nuclear ribonucleoproteins (snRNP) are necessary for removing introns. B. The consensus sequences at the \(5^{\prime}-\) and \(3^{\prime}\) -ends of introns are identical. C. Removal of an intron does not require metabolic energy. D. The exon at one end of an intron must always be joined to the exon at its other end. E. The nucleoside at the end of the intron first released forms a bond with a \(3^{\prime}\) -OH group on one of the nucleotides within the intron.

Short answer

Answer: A. snRNP are necessary for removing introns.

Step-by-step solution

A. snRNP are necessary for removing introns

This statement is correct. Small nuclear ribonucleoproteins (snRNP) are part of the spliceosome complex which is responsible for removing introns from the pre-mRNA during the splicing process. The snRNPs bind to specific sequences on the pre-mRNA to perform their action.

B. Consensus sequences at the ends of introns are identical

This statement is incorrect. The consensus sequences at the \(5'\) and \(3'\) ends of introns are not identical. The \(5'\) splice site has the consensus sequence GU, while the \(3'\) splice site has the consensus sequence AG.

C. No metabolic energy is required to remove an intron

This statement is incorrect. Energy in the form of ATP or GTP is required for the proper functioning of the spliceosome, which is responsible for removing introns and joining exons together.

D. The exon at one end of an intron must always be joined to the exon at its other end

This statement is incorrect. The exon at one end of an intron can be joined to another exon in alternative splicing, which allows for the synthesis of multiple different proteins from a single pre-mRNA.

E. The nucleoside at the end of the intron forms a bond with a \(3'\) -OH group on one of the nucleotides within the intron

This statement is incorrect. In the intron removal process, the \(2'\) -OH group of a branch-point adenosine within the intron attacks the \(5'\) splice site, forming a lariat structure. The \(3'\) -OH group of the upstream exon is then free to attack the \(3'\) splice site, releasing the intron lariat and joining the exons together. The correct statement is A. Small nuclear ribonucleoproteins (snRNP) are necessary for removing introns.