Final answer:
The cellular component that remains at the exon-exon junction to form the exon junction complex (EJC) is mRNA. tRNA is the small, uracil-containing nucleic acid that is covalently bound to amino acids. rRNA, known for its catalytic abilities, is synthesized in the nucleolus.
Step-by-step explanation:
Which cellular component remains at the exon-exon junction to form the exon junction complex (EJC) for export? The answer is A) mRNA. The mRNA molecule carries the coding information from DNA to the cytoplasm and is subsequently translated into protein. Proteins that are part of the EJC bind to the mRNA at the exon-exon junctions after splicing has occurred. This complex is crucial for the export of the mature mRNA from the nucleus to the cytoplasm and also plays a role in mRNA surveillance and translation.
In the context of RNA purification, the description given matches that of D) tRNA, the nucleic acid that transfers specific amino acids to a growing polypeptide chain during protein synthesis. It is relatively small, contains uracil, and most tRNA molecules are covalently bound to an amino acid at one end.
The type of RNA known for its catalytic abilities is C) rRNA. Some rRNA molecules are indeed catalytically active and function as ribozymes, which are part of the ribosome's machinery for protein synthesis. These catalytically active rRNAs are responsible for peptidyl transferase activity, which forms peptide bonds between amino acids.
Lastly, the RNA components of ribosomes are synthesized in the d. nucleolus of the cell. The nucleolus is a specialized structure within the nucleus where ribosomal RNA (rRNA) synthesis and ribosomal subunit assembly occurs.