Question

6. RNA ___________________ is post-transcriptional alteration of sequences in mRNAs.

10. RNA splicing involves two __________ reactions?

14. Peptide bond formation in translation occurs by an _______________catalyzed reaction

17. The protein kinase Raf phosphorylates the protein kinase _______, which then phosphorylates (on both threonine and tyrosine residues) ______________________________.

18. Expression of the immediate early genes triggers the expression of a battery of other downstream genes called ________________________________________________.

Answer 1

6. The nascent RNA synthesized by RNA polymerase II is called heterogenous nuclear RNA (hnRNA) or primary transcript .It contains both unwanted base sequences (introns) alternated with useful base sequences (exons). The process by which this primary transcript is converted into functional mRNA after post-transcriptional processing which involves the process of removal of introns and joining of exons in a defined order is called RNA splicing. So, RNA Splicing is post-transcriptional alteration of sequences in mRNAs.

10. RNA Splicing involves two Trans-esterification reactions. These are removal or splicing of introns and joining of exons. Introns are removed by small nuclear RNA (SnRNA) and protein complex called small nuclear ribonucleoproteins or SnRNPs (Snurps). After the removal of introns, the exons are joined and the excised regions are sealed by Ligase.

14. Peptide bond formation in translation take place between COOH group of first amino acid (methionine) and NH2 group of second amino acid. The formation of peptide bond requires energy and is catalyzed by enzyme peptidyl transferase (a type of ribozyme-catalytic RNA, i.e 23S rRNA in bacteria and 28S rRNA in eukaryotes). So the peptide bond formation in translation occurs by an Peptidyl transferase catalyzed reaction.

17. In unstimulated cells, the Ras protein remain in its inactive form with bound GDP. When a growth factor binds to its receptor tyrosine Kinase (RTK), it leads to the formation of active Ras (GTP bound). This activated Ras initiates a signaling cascades by binding with to the N terminal domain of Raf, a serine/threonine kinase. The protein kinase Raf binds to and phosphorylates MEK, a dual specificity protein kinase that phosphorylates both threonine and tyrosine residues. The MEK in turn phosphorylates and activates MAP kinase by phosphorylating threonine and tyrosine residues. The MAP kinase then phosphorylates many different proteins including transcription factors. So the protein kinase Raf phossphorylates the protein kinase MEK, which then phosphorylates (on both threonine and tyrosine residues) MAP (Mitogen activated Protein) kinase.