Ribozymes is/are
A. Splicing of heterogenous RNA (hnRNA) to form mRNAB. Splicing of polypeptide chain and mRNA
C. Transcription of mRNA
D. Recognition of codons in introns
E. RNA polymerase
Answer. A. Splicing
of heterogenous RNA to form mRNA
; (D) Recognition of codons
in intron
• Ribozymes are RNA molecules with
intrinsic catalytic activity, meeting all the criteria for enzymes definition. These
generally involve transesterification reactions, and ultimately hydrolysis of
phosphodiester bonds in RNA molecules and most concerned with RNA metabolism
(splicing and endoribonuclease). These reactions are facilitated by free-OH
groups e.g. on guanosyl residues. Examples Sn RNAs, rRNA.
(i) Intron splicing events essential for conversion of pm. mRNA to mature RNAs in eukaryotes. Introns don’t code for protein primary transcript while exons codes for proteins are spliced together to form mature mRNA. Small nuclear RNAs (snRNAs) in association with small nuclear ribonucleoprotein particles (snRNPs) facilitate splicing arid thus act as enzyme.
(ii) In eukaryotic protein synthesis
during elongation of polypeptide chain ribozymes (rRNA) involved. The formation
Of peptide bonds is catalyzed by peptidyl transferase, an activity intrinsic to
23S rRNA
found in 50S ribosomal subunit.
• Heterogeneous RNA (hnRNA) are
precursor of mRNA. They are synthesized in nucleus of 75% of hnRNA are degraded in nucleus only 25% of hnRNA forms precussor of mRNA
(pre-mRNA). Splicing of hnRNA forms mRNA pre-mRNA is converted to mRNA.
• Glycine is converted to serine
addition of a methylene group from N5, N’° methylene tetrahydrofolate
Glycine Tetrahydrofolate N5N’°
methylene Serine tetrahydrofolate
