BIOL10221 Molecular Biology Lecture Notes PDF

BIOL10221 “Molecular Biology” Dr David Boam Module 6 - Structure and function of RNA  Aims for this lecture Describe the physical and functional properties of RNA Describe the biological roles of RNA in the cell Describe functions of UTR’s...

BIOL10221 “Molecular Biology” Dr David Boam Module 6 - Structure and function of RNA  Aims for this lecture Describe the physical and functional properties of RNA Describe the biological roles of RNA in the cell Describe functions of UTR’s Lecture 6/1 RNA biochemistry  What is Ribonucleic Acid (RNA)? NA is the product of transcription from a DNA template 10x more RNA than DNA in a cell Several kinds of RNA play key roles in gene expression What makes RNA different from DNA? Chemical structure Physical properties Biological role Lecture 6/1 RNA biochemistry  Chemical Structure of RNA RIBOSE is used in place of Deoxyribose bose contains 2’-OH (hydroxyl) whereas Deoxyribose cks an oxygen, that’s why it’s DEOXY! his makes RNA less stable than DNA Lecture 6/1 RNA biochemistry  Chemical Structure of RNA The base Uracil is used in place of Thymine Uracil does not have a -CH3 (methyl) Lecture 6/1 RNA biochemistry  Biological Roles of RNA Transfer of information from DNA to protein – Messenger RNA (mRNA) codes for proteins Synthesis of Proteins – Ribosomal RNA (rRNA) and Transfer RNA (tRNA) (module 7) Processing of Messenger RNA – Small nuclear RNA (snRNA) involved in splicing introns from pre-messenger RNA (lecture 6/2) Processing and modification of ribosomal RNA – Small nucleolar RNA (snoRNA) - processing and modifying ribosomal RNA Catalytic RNA – Self-splicing introns – Natural and artificially created ribozymes Lecture 6/1 RNA biochemistry  RNA content of a cell A single cell contains 10 pg (10-11 g) RNA 80-85% ribosomal RNA 10-15% low m/w species (tRNAs, small nuclear RNAs etc 1-5% mRNAs Lecture 6/1 RNA biochemistry  Physical Properties of RNA RNA is generally single stranded RNA can base-pair with itself to fold into complex structures Secondary structure Tertiary structure Lecture 6/1 RNA biochemistry How RNA secondary structure forms 5' GCCGCCAG CTGGCGGC 3' CGGCGGTC GACCGCCG 5’ 5' GCCGCCAG CUGGCGGC GACCGCCG Palindromic sequence Self complementary base G C A U pairing C G C G G C C G C G G C Lecture 6/1 RNA biochemistry The regulation of the amount or usage of certain RNA’s is important for their function Controlled by: Synthesis - transcription can be turned on and off rapidly Lac operon 2) Regulated degradation Transferrin receptor mRNA Property of the 3) Translation efficiency - proteins UTRs can control the usage of certain RNA’s e.g. Ferritin mRNA Lecture 6/1 RNA biochemistry  Eukaryotic Class II (mRNA-encoding) genes Transcription start Transcribed region AUG UGA Enhancer Promoter Intron Exons mature mRNA AUG UGA 5'-UTR Translated3'-UTR region Nucleus Cytoplasm H2N COOH Lecture 6/1 RNA biochemistry  The Transferrin receptor Iron in blood binds to Tf-Fe2+ Transferrin - transported into cells TfR via a receptor If there is enough intracellular Fe2+, transferrin receptor mRNA is Fe2+ degraded TfR mRNA Lecture 6/1 RNA biochemistry  RNA 2o structure regulates transferrin receptor mRNA degradation Iron Response Element-binding Intracellular protein (IRE-BP) Iron (Fe ) 2+ AU- rich stab degrad 5’- Coding 3’- le ed UTR region UTR No Fe ….IRE-BP bound to 3’-UTR- RNA stable so 2+ receptor is made In presence of Fe2+ ….IRE-BP binds Fe2+ - dissociates from 3’UTR- RNA degraded so receptor is not made Lecture 6/1 RNA biochemistry  RNA secondary structure can regulate translation: Ferritin – binds Fe2+The Ferritin within the cellgene Low Iron - IRE-BP binds to IRE and prevents translation initiation Fe2+ Fe2+ Lecture 6/1 RNA biochemistry  Summary RNA 2o structure Important for: – Catalysis – Organisation – Recognition Consequences – Stability (transferrin) – Translation (ferritin) Lecture 6/1 RNA biochemistry  Intended learning outcomes for this lecture By completion of this lecture and Keywords supporting material you should be able to rRNA Define and describe the basic tRNA chemical and functional properties of RNA and how it mRNA differs from DNA snRNA Understand how RNA can form secondary structure and build palindrome this into complex three hyphenated dyad dimensional structures symmetry Appreciate the role of RNA UTR secondary/tertiary structure in the biological rolesLecture of RNA6/1 RNA biochemistry