Introns in the eukaryotic genes are found in:
rRNA, tRNA and mRNA encoding genes.
Introns Location in Eukaryotic Genes
Let's understand where introns are located within eukaryotic genes. Eukaryotic genes are different from prokaryotic genes because they contain both coding sequences called exons and non-coding sequences called introns. Introns are segments of DNA that are removed during RNA processing before the RNA molecule becomes functional.
After transcription, the initial RNA molecule, called the primary transcript or pre-mRNA, contains both exons and introns. A process called RNA splicing removes the introns and joins the exons together to form the mature functional RNA.
Presence of Introns in Different RNA Genes
Introns are common in genes that encode messenger RNA (mRNA). These introns are spliced out of the pre-mRNA to produce mature mRNA, which is then translated into protein.
However, introns are not exclusive to protein-coding genes (mRNA encoding genes). They are also found in genes that encode ribosomal RNA (rRNA) and transfer RNA (tRNA). Although less frequent than in mRNA genes, introns in pre-rRNA and pre-tRNA molecules are also removed by splicing, sometimes involving different mechanisms (like self-splicing or enzyme-mediated splicing).
Therefore, introns are present in genes encoding all three major types of RNA in eukaryotes: rRNA, tRNA, and mRNA.
Based on this understanding:
- Option 1 suggests introns are in rRNA and mRNA genes but not tRNA genes. This is incorrect.
- Option 2 suggests introns are in mRNA and tRNA genes but not rRNA genes. This is incorrect.
- Option 3 suggests introns are only in mRNA encoding genes. This is incorrect.
- Option 4 suggests introns are in rRNA, tRNA, and mRNA encoding genes. This is correct.
Thus, introns are found in the genes that encode ribosomal RNA (rRNA), transfer RNA (tRNA), and messenger RNA (mRNA) in eukaryotes.
Important Questions from RNA synthesis and processing
Which one of the following statements related to transcription and processing of mRNA is INCORRECT?
Following statements were made with respect to transcription in eukaryotes:
A. RNA polymerase III synthesises mRNAs in the nucleoplasm
B. The target promoter for RNA polymerase III is usually represented by a bipartite sequence downstream of the transcription start site.
C. The assembly factors TFIIIA and TFIIIC assist the binding of the positioning factor TFIIIB at the precise location.
D. TFIIIB is the last factor that joins the initiation complex.
E. Phosphorylated Ser residues in the C-terminal domain (CTD) of RNA polymerase II serve as binding sites for mRNA processing enzymes.
Which one of the following options represents the correct combination of the statements?
Following statements were made about the post-transcriptional processing of RNA in eukaryotes.
A. Soon after transcription initiation, RNA polymerase II pauses ~30 nucleotides downstream from the site of initiation until the Cap structure is added to the 5' end of the nascent pre- mRNA.
B. The 5' splice sites are functionally divergent whereas the 3' sites are functionally equivalent.
C. In addition to helping in recognition of the splice sites, the exon definition also functions as a splicing regulator by allowing pairing and linking of adjacent 5' and 3' splice sites.
D. The intron definition mechanism applies only to the larger introns (above 500 nucleotides length) and assists in achieving alternate splicing.
E. The splicing reactions carried out in vitro have revealed that the first and second transesterification reactions are reversible.
Which one of the following combination of statements is correct?
Which one of the following statements is NOT a correct feature of Escherichia coli RNA polymerase?
The following statements are related to transcription in bacteria/eukaryotes.
A. During concurrent promoter sequence recognition and melting, melting commences with base flipping where two bases are flipped out into pockets of the primary sigma factor
B. Binding of α-amanitin to RNA polymerase Il permits entry of nucleotides into RNA pol II active site and synthesis of RNA, but prevents translocation
C. RNA polymerase I can use upstream promoters with 3 consensus sequences, as well as internal promoters having a bipartite structure
D. FACT is associated with RNA polymerase during transcriptional elongation and helps displace histone octomers during transcription
Which of the following combinations of statements represents all correct statements?
