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This 6 page Class Notes was uploaded by Jessica Olason on Friday March 27, 2015. The Class Notes belongs to BIO102 at Washington State University taught by Professor Storfer in Fall. Since its upload, it has received 40 views. For similar materials see Biology in Science at Washington State University.
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Date Created: 03/27/15
Week 10 Notes 32315 Protein Synthesis Organism of the day 0 Genderjumping sh They can turn into a male but they can39t go back 0 Protein Synthesis 0 Transcription o Tanslation Steps of protein synthesis 0 DNA transcribed to mRNA 0 mRNA is edited 0 mRNA attaches to ribosome 0 mRNA translated into amino acids Chain of amino acids forms protein 0 Step 1 Transcription DNA to mRNA Messenger RNA mRNA Carries protein building instruction 0 RNA structure 0 Very Similar to DNA structure Phosphate group 0 Sugar 0 Nucleotide base 0 Differences from DNA 0 Sugar is ribose not deoxyribose Uracil U replaces Thymine T o A binds to U 0 RNA is singlestranded Transcription 3 steps 1 Initiation promoter tells RNA polymerase where to start 2 RNA elongation RNA gets longer starts to quotpeelquot away from DNA template 3 Termination transcription stops when RNA reaches quotterminatorquot Step 2 RNA is edited Exons quotcodequot for amino acids lntrons not needed at this point lntrons are spliced out leaving the exons Cao and tail are added 0 After transcription mRNA is spliced Step 3 quotmaturequot mRNA attaches to ribosome Step 4 mRNA translated Translation background genetic code 0 Each triplet of mRNA bases ex UUU is quotcodonquot 0 Each codon is translated into an amino acid 0 64 codon possibilities 4 bases at each site 3 sites 61 code for amino acids 3 quotstopquot codons to end translation This code is universal ALL LIVING THINGS The genetic code 64 codon possibilities quotconservedquot only 20 amino acids 1 quotstartquot codon initiates translation 3 quotstopquot codons End translation Ex Huntington s disease UAU to UAA from conserved to stop which causes problems in genetics genetic disorder 0 Steps of translation 0 Initiation w start codon AUG mRNA molecule binds to ribosome initiator tRNA ts onto ribosome o Elongation mRNA passes between small and large subunits mRNA codons read like a quotticker tapequot tRNA quotanticodonsquot deliver amino acids to ribosome in order speci ed by the mRNA bonds form between adjacent amino acids 0 Termination Stop codon in mRNA moves into ribosome No corresponding anticodon in tRNA Ex gt Ribosome reaches STOP codon UAG gt Protein quotrelease factorsquot tell ribosome to release protein gt mRNA is released proteins called quotrelease factorsquot bind to ribsome mRNA and protein are released 0 RNA 3 types 0 Messenger RNA mRNA Result of transcription Takes quotmessagequot from nucleus to ribosome Has codons o Ribosomal RNA rRNA Site of protein synthesis 0 Transfer RNA tRNA Has quotanticodonsquot to mRNA Each quotanticodonquot attached to appropriate amino acid quottransfersquot amino acids to ribosomes Helps build amino acid chain protein 0 O O O 0 Key Points 0 DNA replication DNA quotunzipsquot and 2 quotdaughterquot strands formed by adding complementary bases 0 Protein synthesis 1 Transcription Like replication but RNA turned to mRNA Editing mRNA edited introns cut out quotmaturequot mRNA attaches to ribosome Translation tRNA quotanticodonsquot bring appropriate amino acids complementary mRNA quotcodonsquot Amino acids chain formed Protein released IhWINI 32515 Lecture outline Types of mutations Results of mutations DNA repair Gene regulation How do Mutations Affect Protein Function Mutations are changes in the base sequence of DNA caused by mistakes during replication or by various environmental factors 0 Five categories of mutations Inversions Translocations Deletions Insertions o Substitutions o Inversions and Translocations o Inversions and transocations occur when pieces of DNA are broken apart and reattached on same or different chromosomes May be relatively benign if entire genes are merely moved from one place to another However if a gene is split in two it will no longer code for a complete functional protein 0 Severe hemophilia often caused inversion in the gene that encodes a blood clotting protein 0 Insertions and deletions o A deletion occurs when one or more nucleotides are removed from the gene sequence 0 An insertion occurs when one or more nucleotides are added to the gene sequence gt Both are called quotframeshift mutationsquot because they can cause shifts in quotreading framesquot 0 Deletions and insertions can cause a misreading of a gene39s codons during transcription or replication gt The codons in THEDOGSAWTHECAT is changed by the deletion of the letter quotEquot to THE 065 AWT HEC AT 0000 gt Or a real example ATG CAT TCG AAA Codes for codons UAG GUA AGC UUU Whichs codes for amino acids TyrValSerPhe gt Now insert ATG CCA 39ITC GGA mRNA UAC GGU AAG CUU U Amino acids TryGlyLysLeu 0 Proteins that result from deletions and insertions often have a very different amino acid sequence and almost always are nonfunctional gt Defective myostatin gene of Belgian Blue cattle has 11 nucleotide deletion generating a premature stop codon o Deletions and insertions of three nucleotides or a multiple of three do not cause a shift of the reading frame and so may simply subtract or add a harmless amino acid to the protein 0 Point mutations or base substitutions 0 May result in change in amino acid sequence 0 When 0 Point Mutations o A point mutation often does not change the amino acid sequence of the protein Because many amino acids are encoded by more than one codon the mutation may cause the same amino acid to be added gt quotsilentquot or quotsynonymousquot substitution gt Ex point mutation in the betaglobin gene for hemoglobin causes CTC to change to C39IT but since both codons code for glutamic acid the protein is unchanged First base substitution usually changes amino acid Second always does Third often doesn39t 0 Sometimes the substituted amino acid may be functionally equivalent to the normal one allowing the mutated protein to function normally Ex in betaglobin point mutation of CTC codon to GTC causes glutamic acid hydrophilic to be replaced with glutamine also hydrophilic but the resulting protein functions well quotneutralquot mutation 0 Some substitutions point mutations can cause altered amino acid sequence that changes protein function dramatically usually for the worse The substitution of an A for T in the CTC lCAC mutation in a hemoglobin gene causes valine hydrophobic to replace glutamic acid hydrophilic Placing this hydrophobic amino acid on the outside of the hemoglobin molecule leas to the clumping of hemoglobin and distortion of the red blood cell seen in sickle cell anemia o A view of mutation o Mutation is the ultimate source of variation Creates variation in DNAproteins Approx 1 in 105 106 eggs or sperm carry a mutation Often neutral or nearly neutral gt Substitutions are often silent When not neutral often negative effects on protein function and organismal tness Sometimes could improve protein function or phenotype gt These mutations may spread through a population Mutation balance example sickle cell anemia o Caused by beta globulin mutation 0 Results in malformed red blood cells Reduction in oxygen capacity Bad shape causing damage to blood vessels and organs 0 BUT maintained in population because change in shape protects against malaria Parasite cannot enter sickleshaped RBCs DNA replication 0 DNA is doublestranded o It quotunzipsquot and new copies of each strand are made by adding complementary bases 1 Enzyme quotunzipsquot DNA in target areas 2 quotbubblesquot form where unzipped 3 DNA polymerases add complementary bases 4 Continues until 2 complete copies made bubbles merge DNA repair 0 DNA replication is not always perfect 0 Ex mismatch 1 in 10000 bases 0 3 steps 1 Damaged DNA recognized 2 Damaged DNA cut out with enzymes 3 Damaged DNA replaced with repair enzymes Are all mutations bad 0 Current thinking is the quotnearly neutralquot model of molecular evolution 0 Most mutations neutral think about conversation of codons 64 codons 20 amino acids 0 Some then detrimental premature stop codons 0 Some few can be bene cial Gene regulation 0 Humans have approx 20500 genes 0 But 38 billion base pair genome MUCH of human DNA is noncoding Some of it is quotjunkquot But some of it is important for initiating protein synthesis etc 0 Even though each cell has a complete genome most cell types ony express certain genes Example of gene expression 0 Some genes expressed only in certain types of cells at certain times or under speci c environmental conditions Ex every cell contains gene for casein milk but this gene expressed only in breast of breast feeding women 0 Gene Turn OnOff in Response to Cues 0 Environmental Cues Bacteria have the ability to reorganize gene expression to match the food resources available 0 Regulation of gene expression 0 Occurs at three different levels 1 2 3 At transcription regulation determines which genes in a given cell are expressed At translation regulation determines how much protein is made from a particular mRNA Proteins can then be kept inactive until needed
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