Large Molecules by University of Arizona Learn about structures and properties of sugars, lipids, amino acids, and nucleotides, as well as macromolecules including proteins, nucleic acids and polysaccharides. Clinical Correlates of pH Levels by University of Arizona Learn how metabolic acidosis or alkalosis can arise and how these conditions shift the bicarbonate equilibrium.
Splicing pathways[ edit ] Several methods of RNA splicing occur in nature; the type of splicing depends on the structure of the spliced intron and the catalysts required for splicing to occur.
Introns[ edit ] The word intron is derived from the term intervening sequence, that is, a segment of DNA that "intervenes" between two exons of a gene.
The term intron refers to both the DNA sequence within a gene and the corresponding sequence in the unprocessed RNA transcript. As part of the RNA processing pathway, introns are removed by RNA splicing either shortly after or concurrent with transcription.
Further upstream from the polypyrimidine tract is the branchpoint, which includes an adenine nucleotide involved in lariat formation.
Y-U-R-A-C branch sequence nucleotides upstream of acceptor site This results in a mature messenger RNA with a missing section of an exon. In this way, a point mutationwhich might otherwise affect only a single amino acid, can manifest as a deletion or truncation in the final protein.
Assembly and activity of the spliceosome occurs during transcription of the pre-mRNA. Two types of spliceosomes have been identified major and minor which contain different snRNPs.
By contrast, when the intronic flanking sequences do not follow the GU-AG rule, noncanonical splicing is said to occur see "minor spliceosome" below. However, in some cases, especially in mRNAs with very long introns, splicing happens in steps, with part of an intron removed and then the remaining intron is spliced out in a following step.
This has been found first in the Ultrabithorax Ubx gene of the fruit fly, Drosophila melanogasterand a few other Drosophila genes, but cases in human have been reported as well.
Group I and II introns perform splicing similar to the spliceosome without requiring any protein. This similarity suggests that Group I and II introns may be evolutionarily related to the spliceosome.
Self-splicing may also be very ancient, and may have existed in an RNA world present before protein. Two transesterifications characterize the mechanism in which group I introns are spliced: The mechanism in which group II introns are spliced two transesterification reaction like group I introns is as follows: The splicing reaction involves a different biochemistry than the spliceosomal and self-splicing pathways.
Prokaryoteson the other hand, splice rarely and mostly non-coding RNAs.
Another important difference between these two groups of organisms is that prokaryotes completely lack the spliceosomal pathway.
Because spliceosomal introns are not conserved in all species, there is debate concerning when spliceosomal splicing evolved. Two models have been proposed:Metabolites Detected by Metabolomic Analysis and Displayed onto Schematic Representations of the Biochemical Pathways (Manipulation of phytoene levels in tomato fruit: effects on isoprenoids, plastids, and intermediary metabolism.
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Aug 18, · 4G_full This is Lecture 4G of the free online course Useful Genetics Part 1. All of the lectures are on YouTube in the Useful Genetics library.
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Systems analysis of the complete genome sequence combined with biochemical information on metabolic pathways has been used to define and elucidate the relationship between genotype and phenotype for Haemophilus influenzae Rd.