BBMB 405 1st Edition Lecture 31Outline of Last Lecture XV. Chapter 29: RNA synthesis and ProcessingC. Transcription in eukaryotes is highly regulated (con’t)Outline of Current Lecture XV. Chapter 29: RNA synthesis and ProcessingC. Transcription in eukaryotes is highly regulated (con’t)D. The discovery of catalytic RNA was revealing in regard to both mechanism and evolutionCurrent LectureXV. Chapter 29: RNA synthesis and ProcessingC. Transcription in eukaryotes is highly regulated (con’t)1. mRNA editing can change protein sequencea. Adenosine deaminases that act on RNA (ADAR) enzymes deaminate adenosineb. ADAR recognizes specific A and catalyzes its conversion to Inosinec. Reads out as G instead of Ad. Adenosine deaminase acting on RNA (ADAR): unedited version allows Ca2+ into ion channel, but with single substitution (A to I converting Gln to Arg) Ca2+ is blocked from the channel; this has a strong effect on the function of the protein2. Cytidine deamination can introduce stop codonsa. C U deamination is catalyzed by APOBEC1These 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.- Apolipotrotein B mRNA editing enzyme 1- Expressed in small intestine, not in liverb. ApoB-100 is synthesized in the liver- Transport of synthesized lipids- Can bind to LDL receptorsc. ApoB-48 is synthesized in the small intestine- Transport of dietary fats- Present in chylomicronsd.3. Pre-mRNAs contain intros that are spliced: discovered because sequences present in DNA, but not in protein4. Chemistry of splicing: transesterficationa.b.c.d. Transesterifcation: alcohol attack ester and replace R groups; no 3’ end so use 2’ hydroxyl of adenosine found in introne. Mg ions: activate nucleophiles (2’ OH or 3’ OH), stabilize leaving groups (phosphates)f. RNA important in this reaction5. Spliceosome is composed of snRNPsa.b. snRNPs are present in nucleolus (not U3 because it is a snoRNA, separate nuclear from nucleolus RNA)c. Subunits make up sliceosome6. Processa. U1snRNP bound to 5’-ssb. Spliceosome assembly and actionc. RNA makes RNA: use for scaffold or sequence specific recognitiond. Structures can be formed between U4 and U6 which needs to be melted prior to activation because U6 needs to form interaction with U2e. U2 and U6 complex coordinates pre-mRNA substrates and catalyzes splicingf. U6 coordinates metal ions for splicingg. U6-U5-U2 complex is recycled7. When does all of this processing occur?a. Prior to export from nucleusb. Pre-mRNA processing occurs co-transcriptionalc. Capping, splicing and poly-adenylation factors interact with transcription elongation complexd. Dependent on phosphorylation state of Pol II C-terminal taile.8. Splicing defects and diseasea. Human hemoglobin beta chainb. Leads to thalassemia (hereditary anemia), patient has to have one blood transfusion per monthc. Mutations affecting splicing have been estimated to cause at least 15% of all genetic diseases9. Alternative splicinga. Alternative splicing can produce multiple isoformsb. Highly regulated through trans-acting protein factors (bind) and cis-regulatory elements (within RNA itself)c. Example: CGRP and Calcitonin have different functionsD. The discovery of catalytic RNA was revealing in regard to both mechanism and evolution1. Self-splicing versus spliceosomal splicinga. Self-splicing: don’t require spliceosome; RNA that fold into structure and bring together ends of intronsb. Group I: first step catalyzed by free nucleotide so no looped intermediatec. Group II: catalyzes exact reaction of spliceosome2. Origin of Life: an RNA world? This may or may not have been how life
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