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CH 17 18 Only pages 351 359 19 1 The function of RNA polymerase how does RNA polymerase differ from DNA polymerase RNA polymerase binds to DNA separates the strands and then uses one of the strands as a template from which to assemble nucleotides into a complementary RNA strand RNA polymerase is important because its ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds or even thousands of RNA molecules RNA polymerase binds only to promoters which are signals in the DNA molecule that show RNA polymerase exactly where to start making mRNA Similar signals in DNA cause transcription to stop when a new mRNA molecule is complete RNA polymerase can initiate RNA synthesis but DNA polymerase requires a primer to initiate DNA synthesis 2 MRNA and primary transcripts In prokaryotes you make an mRNA strand and immediately after you make the mRNA strand you start to translate it In eukaryotes you make your primary transcript then you have to cut out the introns then it s called the secondary transcript Then the 5 prime cap and 3 prime tail are added then it s translated 3 What is a codon What determines the number of possible codons A codon is a specific group of 3 sequential bases of mRNA Each codon codes for a specific amino acid Codons for the same amino acid differ from each other by one base in the third position The sequence of nucleic acids determines the number of possible codons 4 Why the genetic code is redundant but not ambiguous The code is redundant more than one codon per amino acid but not ambiguous no codon specifies more than one amino acid 5 What are the template and non template strands What is their relationship to the sequence of mRNA Whereas the nucleotide strand used for transcription is termed the template strand the non transcribed strand is called the non template strand Transcription occurs 5 prime to 3 prime and translation reads it 5 prime to 3 prime The template strand is the reverse complement The non template strand and the mRNA strand go in the same direction Template strand gets read 3 to 5 prime 6 How a Ribosome reads the message RNA When a ribosome reads a codon on mRNA it must bind to the anticodon of a corresponding tRNA 7 What happens at the E P and A sites A site is where the new incoming tRNA binds to mRNA P site is where the amino acids on the tRNA make a peptide bond with the amino acids on the rRNA at the A site forming a long amino acid chain E site is when the tRNA that just gave up its amino acid now empty exit the ribosome to go restock their amino acid 8 Where is the growing polypeptide Elongation stage of translation 9 TRNA why does it have a defined tertiary structure How is it stabilized what is the anticodon Know all the parts of tRNA Anticodon is complementary to the codon on the mRNA and that codon codes for a specific amino acid tRNA has a defined tertiary structure interaction of the r groups because of the interactions of the nitrogenous bases A lot of R groups have a lot of bonds that they can form so when these things interact with each other they can fold into a tertiary structure 10 How TRNAs are charged what happens if the wrong amino acid is put on a tRNA The enzyme that synthesizes amino Acyl tRNA is called amino acyl tRNA synthase It charges TRNAs in translation If the wrong amino acid is put on a tRNA you would have improper translation causing a mutated protein This doesn t happen in reality 11 The types of mutations that occur in DNA and their consequences Neutral Silent Mutation is a change in the genetic code that is neither harmful nor beneficial Missense Substitution is a single base that replaces another which may result in a codon for a different amino acid Nonsense Substitution is a single base that replaces another that results in the premature termination of a polypeptide Reading Frameshift is a mutation wherein the addition or deletion of a nucleotide s causes a shift in the codons in the mRNA 12 13 How are prokaryotes and eukaryotes similar and different in terms of transcription WHERE Prokaryotes in cytoplasm eukaryotes in nucleus BEGINNING Prokaryotic consensus sequences w in promoter are at 35 TTGACA and 10 TATAAT They do not rely on enhancers or transcription factors Eukaryotic consensus sequences are at 35 and 80 They rely on enhancers and TFs WHAT prokaryotes do not have introns or chromatin Eukaryotes have introns which will be spliced out prior to translation The genes are wrapped up in chromatin which may limit what is available to RNA polymerase HOW 1 RNA Polymerase in prokaryotes 3 in eukaryotes END Prokaryotic RNA goes on immediately for translation Eukaryotic must be processed and transported to the cytoplasm Definitions operon operator promoter repressor activator transcription factor An operon is a stretch of DNA consisting of an operator a promoter and genes for a related set of proteins usually making up an entire metabolic pathway Regulatory proteins bind to the operator to control expression of the operon A promoter is a specific nucleotide sequence in DNA that binds RNA polymerase positioning it to start transcribing RNA at the appropriate place A repressor is a protein that inhibits gene transcription In prokaryotes this problem binds to the DNA in or near the promoter Activators bind to DNA enhancer regions A transcription factor is proteins that assemble on a eukaryotic chromosome allowing RNA polymerase 2 to perform transcription 14 The concept of repressible transcription lac and trp operons On Anthony s study guide The concept of activation of transcription Look on Anthony s operon sheet RNA and enzyme stability as a control mechanism Why are viruses infectious agents What are they 15 16 17 Jsdbnosd made of 18 Viruses are made of a protein capsid and DNA or RNA Viruses can t survive and reproduce on their own so they have to infect things to survive and reproduce What are the lytic and lysogenic cycles of bacteriophage Lytic cycle Phage causes lysis and death of host cell Lysogenic cycle Prophage DNA incorporated in host DNA Lytic cycle 1 Phage attaches by tail fibers to host cell 2 Penetration Phage lysozyme opens cell wall tail sheath contracts to force tail core and DNA into cell 3 Biosynthesis Production of phage DNA and proteins 4 Maturation Assembly of phage particles 5 Release Phage lysozyme breaks cell wall Lysogenic cycle 1 Phage attaches by tail fibers to host cell 2 Penetration Phage lysozyme opens cell wall tail sheath


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