Question

What role do small nucluar ribomucleagroteins I.5 On what basis is a promoter of a gene strong ar weak?

Answer 1

II 3] EF-Tu is a prokaryotic elongation factor responsible for catalyzing the binding of an aminoacyl-tRNA [aa-tRNA] to the ribosome. It is a multifunctional G-protein. Besides binding of aa-tRNA to the ribosome it also possesses chaperone activity in protecting other proteins from aggregation caused by environmental stress, displays a protein disulfide isomerase activity and participating in degradation of N-terminally blocked proteins by the proteosomes.

Its most important role is in elongation phase of protein synthesis. This is done via three steps-

i] EF-Tu binds GTP and aminoacyl-tRNA, which leads to the codon dependent placement of the aminoacyl -tRNA at the A-site of the ribosome, GTP hydrolysis, and the release of EF-Tu-GDP from the ribosome.

ii] EF-Ts[ elongation factor Ts] facilitates the exchange of EF-Tu bound GDP for GTP.

iii] Upon the peptide bond formation, EF-G [ elongation factor G] tranlocates the mRNA one codon to allow for arrival of new aminoacyl-tRNA in the A-site.

II 4] Small nuclear ribonucleoproteins [snRNPs] are RNA-protein complexes that combine with unmodified pre-mRNA and other proteins to form a spliceosome- a large RNA-protein complex upon which splicing of pre-mRNA occurs. A spliceosome is a large and complex molecular structure found primarily within the nucleus of eukaryotic cells. They are assembled from snRNA and about 80 proteins. The spliceosomes remove introns from a transcribed pre-mRNA which is actually a type of primary transcript.

II 5] A promoter is a sequence of nucleotides present upstream of a gene at which the RNA polymerase binds and initiates the transcription process. A promoter is considered weak or strong based on its affinity for RNA polymerase and the sigma factor. If the consensus sequence of promoter matches that of the RNA polymerase, it is considered as strong. On the other hand, if the sequences do not match exactly, it is called a weak promoter. This affects the process of protein synthesis.