1/23/2019 chapter 17 reading guide - Google Docs What did Garrod mean by "inborn errors of metabolism" Symptoms of an inherited disease reflect an inability to synthesize a certain enzyme. Beadle and Tatum Exposed bread mold to xrays. Each mutation causes an inability to produce specific enzymes, therefore the mutation is classified by what the mold needs/ uses to grow. What was Beadle and Tatum's initial hypothesis? One gene one enzyme Beadle and Tatum's final hypothesis One gene one polypeptide Summarize the 2 major stages in getting DNA to protein Transformation­ ribosomes synthesize using RNA Transcription­ synthesis of RNA into DNA, nucleus Difference between flow of information in prokaryotic vs. eukaryotic cell pro ­ cell space and ribosome, no RNA processing euk ­ transcription and RNA processing in neucleus, translation in ribosome Central dogma DNA ­> RNA ­> Protein exon shuffling The variation in the patterns by which RNA may produce diverse sets of exons from a single gene. tRNA transfer RNA; type of RNA that carries amino acids to the ribosome anticodon A three­nucleotide base sequence on tRNA aminoacyl­tRNA synthetase An enzyme that joins each amino acid to the appropriate tRNA. polyribosomes Found in eukaryotic and prokaryotic cells, enable a cell to make many copies of a polypeptide very quickly post­translational modification the removal of some amino acid segments; folding the protein; stabilizing protein with disulfide bridges; adding carbohydrates https://docs.google.com/document/d/1jYCr6wpHLG6cSAzcXQy2Uhsdo-6rpY2zQRF-8OHfESw/edit 1/6 1/23/2019 chapter 17 reading guide - Google Docs signal peptides sequence of about 20 amino acids on the leading end of the polypeptide SRP a signal recognition particle protein that binds the signal sequence and stops translation, then later moved to the rough ER to be translated at the same time as being imported mutations A random error in gene replication that leads to a change point mutation A change in a gene at a single nucleotide pair. Nucleotide­pair substitution the replacement of one nucleotide and its partner with another pair of nucleotides silent mutations base­pair substitutions with no effect on genetic code because of redundancy missense mutations still codes for an amino acid, but not necessarily the right amino acid nonsense mutation A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein. insertions A mutation involving the addition of one or more nucleotide pairs to a gene. deletions Mutation involving the removal of one or more nucleotide pairs from a gene frameshift mutation Mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide mutagen A chemical or physical agent that interacts with DNA and causes a mutation. How is bacterial and eukaryotic gene expression different pro: don't travel euk: leave nucleus ­> ribosomes; includes rna processing transcription summary (euk) https://docs.google.com/document/d/1jYCr6wpHLG6cSAzcXQy2Uhsdo-6rpY2zQRF-8OHfESw/edit 2/6 1/23/2019 chapter 17 reading guide - Google Docs pre­mRNA is cleaved while RNA polymerase II continues to transcribe DNA ­> proteins cut it free from polymerase (releasing pre­mRNA) ­> polymerase falls off the DNA and transcription is terminated Why does the "code" have to be in triplets and not singles or doubles? Triplets are the smallest units of uniform length that can code for all the amino acids What is the template strand? It provides the template for ordering the sequence of nucleotides in an RNA Codon and anticodon they both consist of 3 RNA molecules, but codons are found in mRNA and anticodons are found in tRNA What is the reading frame? Our ability to extract the intended message from a written language depends on reading the symbols in the correct groupings What can be drawn from the similarities of genetic code among living organisms? Genes can be transplanted from one organism to another. It shows common ancestry. What is a transcription unit? a stretch of DNA that is transcribed into an RNA molecule Prokaryotic promoter and terminator Promoter is the DNA sequence where RNA polymerase attaches and initiates transcription. Terminator is the sequence that signals the end of transcription Termination of transcription for prokaryotic organisms transcription proceeds through a terminator sequence in the DNA, and at the end it stops Termination of transcription for eukaryotic organisms transcription pre mRNA is cleaved from growing RNA chain while polymerase 2 continues and it keeps reading after it releases Why is it important that the promoter be upstream of the transcription unit? it has to read it left to right because the promoter must be before codons Why is RNA processing necessary? it helps form on mRNA molecule that is ready to be translated. What does adding a 5' cap and poly A tail mean and why is it important? https://docs.google.com/document/d/1jYCr6wpHLG6cSAzcXQy2Uhsdo-6rpY2zQRF-8OHfESw/edit 3/6 1/23/2019 chapter 17 reading guide - Google Docs it helps form on mRNA molecule that is ready to be translated, and it facilitates export of mature mRNA from the nucleus, protects, mRNA from degradation from hydrophilic enzymes, and it helps ribosomes attach to 5' end of mRNA RNA Splicing removes introns and joins exons Introns noncoding segments of nucleic acids Exons coding regions of nucleic acids Spliceosome assembly of snrnps and protein that release exons and gain introns snRNP's short nucleic segment at the end of the inton that signals where its going to splice Ribozymes RNA molecules that function as enzymes UTR intron untranslated regions Alternative RNA splicing single gene codes for 2 or more polypeptides depending on which segments are treated as exons during RNA processing Domains discrete structural and functional regions Structure and function of transfer RNA it consists of a single strand that is looped, and it contains anticodons that match mRNA codons Why is enzyme aminoacyl­tRNA synthetase important to translation and protein synthesis? if there is a mutation, then the enzyme won't join the correct amino acid What is "wobble"? flexible base pairing at the third base of codon Structure and function of ribosomal RNA https://docs.google.com/document/d/1jYCr6wpHLG6cSAzcXQy2Uhsdo-6rpY2zQRF-8OHfESw/edit 4/6 1/23/2019 chapter 17 reading guide - Google Docs ribosomal RNA aids in building the protein from the amino acids that the tRNA attaches on the mRNA. It has two subunits, and 3 binding sites Steps of initiation of translation Ribosomal sub units binds to both mRNA and a specific initiator tRNA. tRNA pairs with a start codon. Large sub units attach and form initiation complex. Initiator tRNA is now in the P site, and then a site is available for next tRNA Elongation of cycle of translation a charged tRNA docks in the A site and the existing, growing polypeptide is transferred from the tRNA molecule in the P site to the new tRNA's amino acid. The ribosome then moves 3 bases along the mRNA, moving the uncharged tRNA in the P site into the exit site, the tRNA in the A site into the P site, and positioning a new codon into association with the A site. How translation is terminated translocation brings a stop codon into the position associated with the empty A site. A stop codon does not code for an amino acid, but for a release factor. The release factor binds and then frees the polypeptide and dissociates the ribosome. Polyribosomes strings of ribosomes trailing along the same mRNA, makes many copies of a polypeptide very quickly Signal peptide amino acids near the landing end of a polypeptide Signal recognition particle functions as an adapter that brings the ribosome to a receptor protein built into the ER membrane Mutations changes in the genetic information of a cell Point Mutations chemical changes in a single base pair Base­pair substitution replacement of a nucleotide and its partner with another air of nucleotides Missense charge of one amino acids to another, may have little effector protein Nonsense codon changed to a stop codon, translation is terminated prematurely, leads to nonfunctional proteins https://docs.google.com/document/d/1jYCr6wpHLG6cSAzcXQy2Uhsdo-6rpY2zQRF-8OHfESw/edit 5/6 1/23/2019 chapter 17 reading guide - Google Docs Insertions addition of a nucleotide pair Deletions loss of a nucleotide pair Frameshift mutation altered reading frame due to addition or deletion of a nucleotide pair Mutagen physical or chemical agents that interact with DNA to cause mutations How has a gene been "redefined" and why? it is now defined as a region of DNA that can be expressed to produce a polypeptide or an RNA molecule https://docs.google.com/document/d/1jYCr6wpHLG6cSAzcXQy2Uhsdo-6rpY2zQRF-8OHfESw/edit 6/6
