The mature mRNA is then exported to the cytoplasm What is minor splicing? some introns in the pre-mRNA of multicellular eukaryotes can undergo this type of splicing if introns have different consensus sequences at the 5' splice site and branch point. Next, cleavage at the 3' splice site occurs while the 3' of Exon 1 becomes covalently attached to the 5' of Exon 2. This bond is formed via a transesterification reaction. The intron first cleaves at the 5' splice site and then the free 5' end of the intron folds back on itsself and binds to the branch point, forming a structure called a lariat. Splicing takes place within a spliceosome, which consists of 5 snRNAs, which associate with proteins to form a total of 5 snRNPs (U1, U2, U4, U5, and U6). Additional sequences in introns and exons can also affect the process of splicing. The 5' splice site, branch point, and 3' splice site are collectively called the *splicing code* becaise it determines where splicing will occur. Mutation of this nucleotide will also prevent splicing. The third sequence important for splicing is the *branch point* which is an adenine nucleotide upstream of the 3' splice site. indeed, changing a nucleotide at either of these sites will prevent splicing. These sites possess short consensus sequences - most introns in pre-mRNA begin with GU and end with AG indicating their important role in splicing. The ends of the intron are called its 5' and 3' spice sites. Splicing requires the presence of 3 sequences in the intron. Since the amount of protein not only depends on the amount of RNA transcribed, but also the stability of the DNA molecule, this poly(A) increases the amount of protein synthesized by protecting the 3' end from degredation by exonucleases, and subsequently increasing the time in which the mRNA stays in tact and available for translationÄescribe RNA splicing of eukaryotic mRNA This modification of eukaryotic pre-mRNA takes place in the nucleus, prior to its transport to the cytoplasm. Once cleavage is complete, adenosine nucleotides are added without a template to the 3' end. A large number of proteins help to find the cleavage site and cleave the 3' at the cleavage site. Downstream of the cleavage site is typically a sequence rich in uracil, or U and G. The consensus sequence AAUAAA (called the poly(A) consensus sequence) is usuallu 11-30 nucleotides upstream of the cleavage site and determines the point at which cleavage will take place. Processing of the 3' end of pre-mRNA requires sequences, collectively termed the polyadenylation signal, located both upstream and downstream of the cleavage site. This sequence affects the stability of mRNA and helps regulate the translation of the mRNA protein-coding sequence this is a sequence of nucleotides at the 3' end of an mRA strand that is not translated into AAs. 3' untranslated region (3' UTR) aka the "trailer". This region begins with a start codon and ends with a stop codon 3. protein-coding region - which comprises the condons that specify the AAs of the proteins. In bacteria, this region contains a consensus sequence called the Shine Dalgarno Sequence. this is a sequence of nucleotides at the 5' of the mRNA that does not encode any of the AAs of a protein. the 5' unsaturated region (5' UTR) or aka the "leader". Both eukaryotic and prokaryotic mRNA contains 3 primary regions: 1. In an mRNA molecule, each AA of a protein is specified by a set of 3 nucleotides, called a codon. It carries genetic info from DNA to a ribosome, where it helps to assemble AA in their correct order. It should be noted, that S1 is only present in Gram-negative bacteria, being absent from Gram-positive species.MRNA functions as the template for protein synthesis. What principally attracts ribosome to mRNA initiation region is apparently ribosomal protein S1, which binds to AU-rich sequences found in many prokaryotic mRNAs 15-30 nucleotides upstream of start-codon. Moreover, numerous prokaryotic mRNAs don't possess Shine-Dalgarno sequences at all. In Gram-negative bacteria, however, Shine-Dalgarno sequence presence is not obligatory for ribosome to locate initiator codon, since deletion of Anti-Shine-Dalgarno sequence from 16S rRNA doesn't lead to translation initiation at non-authentic sites. When the Shine-Dalgarno sequence and the anti-Shine-Dalgarno sequence pair, the translation initiation factors IF2-GTP, IF1, IF3, as well as the initiator tRNA fMet-tRNA(fMET) are recruited to the ribosome. This reduction is due to a reduced mRNA-ribosome pairing efficiency, as evidenced by the fact that complementary mutations in the anti-Shine-Dalgarno sequence can restore translation. Mutations in the Shine-Dalgarno sequence can reduce translation. Safe Weighing Range Ensures Accurate Results
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