Harper's Biochemistry Chapter 36 - RNA Synthesis, Processing, & Modification PDF

C H A P T E R RNA Synthesis, Processing, & Modification P. Anthony Weil, PhD 36 OBJ EC T IVES Describe both the molecules involved and the mechanism of RNA...

C H A P T E R RNA Synthesis, Processing, & Modification P. Anthony Weil, PhD 36 OBJ EC T IVES Describe both the molecules involved and the mechanism of RNA synthesis. Describe the major differences between the prokaryotic and eukaryotic After studying this chapter, transcription machineries. you should be able to: Explain how eukaryotic DNA-dependent RNA polymerases, in collaboration with an array of specific accessory factors, can differentially transcribe genomic DNA to produce specific messenger RNA (mRNA) precursor molecules. Diagram the critical functional elements of eukaryotic mRNA encoding genes and detail important similarities and differences with their prokaryotic counterparts. Describe the key structural elements of eukaryotic mRNA precursors as well as their fully processed forms. Appreciate the fact that the majority of mammalian mRNA-encoding genes are interrupted by multiple nonprotein coding sequences termed introns, which are interspersed between protein coding regions termed exons. Explain that since intron RNA does not encode protein, the intronic RNA must be specifically and accurately removed in order to generate functional mRNAs from the mRNA precursor molecules in a series of precise molecular events termed RNA splicing. Explain the steps and molecules that catalyze mRNA splicing, a process that converts the end-modified precursor molecules into mRNAs that are functional for translation. BIOMEDICAL IMPORTANCE hese proesses resuls in lered res of proein synhesis, nd hus,  vriey of ellulr phenoypi hnes. Suh ler- The synhesis of n RNA moleule from eukryoi DNA is  ions in ene expression llow ornisms o dp o hnes omplex proess involvin one of he roup of DNA-dependen in heir environmen. I is lso how differenied ell sru- RNA polymerse enzymes nd  number of ddiionl proeins. ures nd funions re esblished nd minined. Errors or The enerl seps required o synhesize he primry rnsrip hnes in synhesis, proessin, spliin, sbiliy, or funion re iniiion, elonion, nd erminion. Mos is known of mRNA rnsrips n be  use of disese. bou iniiion. A number of DNA reions (enerlly loed upsrem from he iniiion sie) nd proein fors h bind o hese sequenes o reule he iniiion of rnsripion RNA EXISTS IN TWO MAJOR hve been idenified. Cerin RNAs—mRNAs in priulr— hve very differen life spns in  ell. The RNA moleules CLASSES synhesized in mmmlin ells re mde s preursor mol- All eukryoi ells hve wo mjor lsses of RNA (Table 36–1), eules h hve o be proessed ino mure, ive RNA. I heprotein coding RNAs, or mRNAs, nd vrious forms of bun- is imporn o undersnd he bsi priniples of messener dn nonprotein coding RNAs delineed on he bsis of size: RNA (mRNA) synhesis nd mebolism, for modulion of he lre ribosoml RNAs (rRNAs) nd lon nonodin RNAs 384  CHAPTER 36 RNA Synthesis, Processing, & Modification 385 TABLE 36–1 Classes of Eukaryotic RNA RNA Distinct Forms Abundance Stability Protein Coding RNAs Messenger (mRNA) ≥105 Different species 2-5% of total Unstable to very stable Nonprotein Coding RNAs (ncRNAs) Large ncRNAs Ribosomal (rRNA) 28S, 18S 80% of total Very stable lncRNAs ~1000s ~1-2% Unstable to very stable Small ncRNAs 5.8S, 5S ~2% Very stable Small ribosomal RNAs Transfer RNAs (tRNAs) ~60 Different species ~15% of total Very stable Small nuclear (snRNA) ~30 Different species ≤1% of total Very stable Micro/Silencing (mi/SiRNAs) 100s-1000