BIO 172 1st Edition Lecture 7Outline of Last Lecture I. DNA replicationII. TranscriptionOutline of Current Lecture I. mRNA ProcessingII. TranslationCurrent LectureRNA Processing: Prokaryotes use RNA intranslation, becauseboth Transcription andTranslation happen inthe cytoplasm!Eukaryotes need toprocess RNA before itcan be used; becausetheir cells have anucleus.Modifications RNA goes through before it leaves the Nucleus in Eukaryotes:Add 5’ cap. (5’ to 5’ Phosphate linkage)Add poly A tail to 3’ end. Both these events happen after transcription! The 5’ Cap helps stabilize and get RNA ready for translation. Tail helps stabilize and export from the nucleus.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.A third event if RNA Splicing: Removing introns. Removal of introns is done by spliceosomes. Introns are portions of the RNA not used in translation.snRNPS: Small RiboNuclear Proteins. These proteins catalyze splicing of the mRNA, so the mRNAcan become a mature mRNA transcript. RNA within asnRNP finds the junction, and then the “A” can attack the junction. Breaks the junction, and then the intron is gone!1 32 4snRNPshold together the loop, and releases the intron. Then the 5’ cap endattaches to the 3’ and it’s now mature RNA! (step 4 above)*Bacteria typically don’t have many introns. Eukaryotes though, every gene has introns! Alternative splicing: exons attached, might leave out one exon… the proteins will be different based on which exon is left out. The order or how many exons come together makes proteins carry out different functions. Going through alt splicing allows more proteins to come from fewer genes. It is important for eukaryotes to get more out of their genome, more proteins for each coding region.Introns are spliced out by spliceosomes before the mRNA is translated.mRNA processing pretty much only happens in Eukaryotes.Translation:Need a ribosome to bind to mRNA to initiate translation, initiation factors help start translation.Aminoacyl tRNA synthetases: take a tRNA (uncharged, not carrying an amino acid) and then it puts the amino acid on the tRNA, which gives it a charge.Basic Features of Translation: Synthesis of a Polypeptide using information in mRNA.Carried out by a ribosome.Occurs in the Cytosol.mRNAis carrying DNA info, because mRNA is complementary to its template- DNA!. tRNAis carrying amino acid, and it reads the mRNA. Prokaryotes: mRNA transcribed in the cytoplasm of Prokaryotes. The ribosome can jump right on to begin translation.Eukaryotes: mRNA has to leave the nucleus, where it was transcribed. Translation requires three types of RNA:mRNA (messenger) – specifies the sequence of amino acids in a proteinrRNA (ribosomal RNA) – component of ribosomes. Makes up ribosomes, it is a complex of rRNA and protein.tRNA (transfer RNA) – links nucleic acid information to amino acidsGoing from DNA… to RNA (mRNA)… to Protein. Three Nucleotides in mRNA = 1 codon.DNA template- make an RNA species from that. Then tRNA pairs with a codon of mRNA.The following chart is important: You need to be able to follow the color scheme and order of the bases (CUA, for example).Always read code from 5’ to 3’ on mRNA. This chart is 5’ to 3’ Left to Right.More than one codon can specify for an amino acid! Redundancy is usually in the third position.Where the ribosome and DNA have the first two with good base pairing, the third is not so important.Always read code from 5’ to 3’ on mRNA, and recognize START and STOP codons: AUG in bacteria codes for “formal methionine” with initiates tRNA. It’s a start codon.Release factor in stop codon causes ribosome to disassemble. tRNA help read the mRNA code and insert the correct amino acid.Short RNAs with intra-molecular base pairing (so bases pair with other bases in that single RNA strand).One part (Anti-codon) base pairs with codon of mRNA. Anticodon loop pairs with codon in mRNA and specifies the amino acid. Amino acid attaches to 3’ end.One end is attached to the specific amino acid.(see diagram on next page):1. Active site on aminoacyl tRNA synthetase binds ATP and amino acid. Each aminoacyl tRNA synthetase is specific to one amino acid.2. Reaction leaves AMP and amino acid bound to enzyme; two phosphate groups released. “Activated” amino acid has high potential energy. 3. The activated amino acid is transferred from tRNA synthetase to the tRNA specific to that amino acid; AMP leaves.4. The finished aminoacyl tRNA is ready to participate in translation.Specific for leucine! Unlinked tRNA is “uncharged tRNA”.This reaction does not make errors often. The ANTICODON varies and then tRNA has a reaction with the anticodon so it knows which base to link.Bind each required tRNA so there’s a link, for amino acid to link at 3’ end.RIBOSOME: both prokaryotes and eukaryotes have a small and large subunit. The total size based on where they migrate within a gradient.The Large Subunit includes three binding sites for tRNAs:E site: where the tRNA that exits the ribosome goes. This tRNA no longer has a charge.P site: making a peptide bond. Holds the bases while the peptide bond forms.A site: charged tRNA entering, the tRNA is charged because it has an amino acid attached. As ribosome begins translating.These three sites work as translation occurs.Peptide bond formation, and then the ribosome moves along the strand.Initiation of Translation:1. Small subunit of ribosome attaches to the 5’ end of mRNA. (at the ribosome binding site). Ribosome binding site sequence binds to a complementary sequence in an RNA molecule (in the small subunit of the ribosome) with the help of protein initiation factors.mRNA has a ribosome binding site.2. Initiator animacyl tRNA (attached to “formal-Met”) binds to start codon (AUG).Initiator pairs with AUG start codon. Leaves “formal-Met” and is sitting in P-site.3. Large subunit of ribosome binds (initiator tRNA occupies P site). Translation begins.1. Incoming aminoacyl tRNA. New tRNA moves into A site, where its anticodon base pairs with the mRNA codon. Amino acid alone in the A site, then the ribosome catalyzes.2. Peptide bond formation. The amino acid attached to the tRNA in the P site is transferred tothe tRNA in the A site. Ribosome helps the peptide bond formation take place, then once the tRNA no longer has a charge, it moves to