BO101 Molecular Genetics Lecture 4 Expression of Genes PDF

Expression of Genes BO101 - Molecular Genetics - Lecture 4 Dr Andrew Flaus, Biochemistry Flickr - Stewart Butter eld - Library fi Proteins perform many functions based on their structures Proteins: Getting things done ๏ Diverse structures enables wi...

Expression of Genes BO101 - Molecular Genetics - Lecture 4 Dr Andrew Flaus, Biochemistry Flickr - Stewart Butter eld - Library fi Proteins perform many functions based on their structures Proteins: Getting things done ๏ Diverse structures enables wide range of functions ‣ Enzymes: digestion ‣ Ovalbumin: storage ‣ Antibodies: defence ‣ Hemoglobin: transport ‣ Receptors: signalling ‣ Keratin: structures ‣ Insulin: coordination ‣ Actin-myosin: movement Campbell g 5.13 fi Protein function depends on structure ๏ Biochemical properties determine structure to enable function ‣ Antibody protein surface matches target antigen Enables recognition function ‣ Hemoglobin protein pockets t heme chemical that binds iron Enables iron to transport oxygen Campbell g 5.17, 5.18f fi fi Proteins must fold for biological activity ๏ Folded protein ‣ Final stable structure ‣ Active ๏ Denatured protein ‣ Unfolded ‣ Inactive Campbell g 5.20 fi Four levels of protein structure ๏ 1º structure ‣ Linear order of amino acids ๏ 2º structure ‣ Hydrogen bonding between nearby amino acids in backbone ๏ 3º structure ‣ Stabilisation by interaction between sidechains ๏ 4º structure ‣ Close association of two or more polypeptide chains Campbell g 5.18a-c fi Proteins from amino acid building blocks ๏ Proteins are polymers of amino acids ๏ Common features ‣ Amino group ‣ Carboxylic acid group ‣ Central alpha carbon ๏ Unique feature of each type ‣ Sidechain, R Campbell p125 Amino acid polymers link by peptide bond ๏ Links up linear protein backbone ‣ 50-5000 amino acids ๏ Peptide bond ‣ Covalent bond between amino acids in backbone Amino group Carboxyl group ๏ Polypeptide chain has N and C termini Campbell g 5.15 fi 20 amino acid types = sidechains ๏ Sidechains confer unique properties to amino acids ‣ 20 different types ‣ Chemical toolkit ๏ Chemical types 1. Hydrophobic, non-polar 2. Uncharged hydrophilic, polar 3. Charged hydrophilic, ionic Campbell g 5.14 fi Flow of genetic information Central dogma of molecular biology Directional ow of genetic information “Once sequence information has passed to a protein it cannot get out” Crick, 1956 Campbell Biology ch 17 concepts fl Genetic code: DNA translated to protein ๏ Universal code ‣ Genetic information in DNA directs creation of functional proteins Primary structure = order of amino acids ‣ Same in all living organisms Prokaryotes and eukaryotes Campbell Biology g 17.4 fi Genetic code: Translates DNA to protein ๏ Universal code ๏ Codons ‣ 20 amino acids but 4 bases Need multiple bases to encode each amino acid 4x4x4 = 43 = 64 possible codons ‣ Groups of 3 nucleotides 4 possibilities in position 1 4 possibilities in position 2 4 possibilities in position 3 ‣ Frames to step along code Campbell Biology g 17.5 fi Genetic code is redundant ๏ Universal code ๏ Codons ‣ Groups of 3 nucleotides ‣ 4x4x4 = 43 = 64 possible codons ๏ Redundant ‣ 20 amino acids use 61 codons Redundancy = more than 1 codon for most amino acids ‣ Stop (3 codons) ‣ Start (1 codon, shared) Campbell Biology g 17.6 fi Transcription makes mRNA Stages of transcription 1. Initiation ‣ RNA polymerase binds to start ‣ Transcription factors assist (TFs) To be covered in lecture 5 2. Elongation ‣ RNA polymerase moves 5’ to 3’ ‣ Polymerises RNA based on template DNA strand 3. Termination ‣ RNA polymerase detaches Able to restart another cycle Campbell Biology g 17.8 fi Stages of transcription 1. Initiation 2. Elongation ‣ RNA polymerase Moves 5’ to 3’ Does NOT need a primer ‣ Polymerises transcript based on template strand Uracil (U) opposite Adenine (A) ‣ Separation of DNA strands 3. Termination Campbell Biology g 17.10 fi Campbell Biology - BioFlix - Protein Synthesis - Transcription: 0.28-0.53 RNA post-transcriptional processing ๏ Only in eukaryotes 1. mRNA capping ‣ Protective 2. polyA tail ‣ Stabilisation Campbell Biology g 17.11 fi RNA post-transcriptional processing 3. Splicing ‣ Removes INTRONS Concatenates EXONS ‣ Makes mature mRNA Protein coding exons only Enables variation in proteins encoded Campbell Biology 17.12, 17.13 Campbell Biology - BioFlix - Protein Synthesis - RNA processing: 0.52-1.33 Translation of mRNA to protein Translation machinery ๏ mRNA ‣ Processed transcript ‣ ‘Blueprint’ sequence of codons ๏ tRNA ‣ Adapter holds matching anticodon and amino acid ๏ Ribosome ‣ Enzyme that chains amino acids into a polypeptide Campbell Biology g 17.15 fi Campbell Biology - BioFlix - Protein Synthesis -Translation: 1.31-2.41 tRNAs ๏ Adapter with two ends ‣ Amino acid attachment ‣ Anticodon loop matches mRNA ๏ Amino acid charging ‣ tRNA synthetase enzymes Campbell Biology g 17.16, 17.17 fi Campbell Biology - BioFlix - Protein Synthesis -Translation: 2.16-2.41 Ribosomes ๏ Two parts ‣ Small subunit binds mRNA ‣ Large subunit holds machinery ๏ E-P-A sites in ribosome ‣ tRNA matches codon at A site ‣ Peptide bond formed at P site ‣ Empty tRNA leaves at E site ๏ Ribosomes are processive ‣ Step along mRNA template Campbell Biology g 17.18 fi  BioFlix Protein Synthesis Ribosome: 1.43-2.15  Campbell g 17.25 fi  gene a region of DNA that can be expressed to produce a nal functional product that is either a polypeptide or an RNA molecule fi Mutations and protein function Types of mutation ๏ Wild type ‣ Normal sequence ๏ Mutation ‣ Change in coding sequence ‣ Substitution mutations ‣ Frameshift mutations Campbell Biology g 17.26 fi Types of mutation: Substitution 1. Substitution mutations ‣ Change of nucleotides ‣ Possible outcomes a. Silent = same amino acid b. Missense = different amino acid c. Nonsense = Stop codon 2. Frameshift mutations Campbell Biology g 17.27 fi Types of mutation: Frameshift 1. Substitution mutations 2. Frameshift mutations ‣ Insertion or deletion of nucleotides Changes ribosome reading frame ‣ Possible outcomes: a. Premature Stop codon soon after b. Many incorrect amino acids added c. Minor effect, if frameshift is multiple of 3 Campbell Biology g 17.26 fi Mutation and disease ๏ Sickle cell hemoglobin ‣ Single mutation in DNA ‣ Change in amino acid sequence of hemoglobin ‣ Clumping of hemoglobin ‣ Stretched ‘sickle’ red blood cells ‣ Reduced oxygen transport ๏ Molecular basis of genetic diseases http://evolution.berkeley.edu/evolibrary/article/mutations_06 Summary of lecture ๏ Proteins ‣ Worker molecules of cell ‣ 4 levels of structure ๏ Central dogma ‣ DNA-RNA-Protein ๏ Transcription ‣ RNA polymerase ๏ Translation ‣ tRNA, ribosomes, export ๏ Mutations ‣ Genetic basis of disease  Learning outcomes for lecture ๏ On successful completion of this lecture, you will be able to: ‣ Relate the basic aspects of protein structure and function ‣ List the 4 levels of protein structure ‣ De ne a gene ‣ Name the basic steps in the ow of genetic information from DNA to RNA to protein ‣ Describe the steps by which a mRNA template is made from DNA, including transcription and post-transcriptional processing ‣ Describe the steps by which proteins are produced based on mRNAs, including translation by ribosomes and post-translational events ‣ Explain the effect of mutations on protein coding genes fi fl