Lecture 7 Notes Gabs The Central Dogma Information in a eukaryotes and prokaryotes goes from DNA to RNA to protein In some instances RNA can ow to DNA Mechanism is similar in prokaryotes and eukaryotes However eukaryotes have to make some modi cations to work around dif culties Eukaryotic chromosomes are highly packed into chromatin DNA takes up space so chromatin condenses it Prokaryotes don t have as much DNA so it just oats around DNA is in nucleus but machinery for protein synthesis is in cytosol the solution in the cell not held by any organelles DNA synthesis replication RNA synthesis transcription protein synthesis translation Transcription creates single stranded RNA molecule DNA has a template and a non template strand RNA is complimentary to template strand but is identical to non template strand RNA Transcription Synthesis of DNA only occurs in one direction RNA synthesized 5 to 3 end DNA is read 3 to 5 end by RNA polymerase DNA strands are anti parallel Eukaryotes have 3 types of RNA polymerase prokaryotes have 1 which synthesize different types of RNA Transcription starts at a promoter a speci c DNA sequence Prokaryotes RNA polymerase binds strongly to promoter sequence beginning Eukaryotes general transcription factors help position RNA polymerase allowing transcription it to begin transcription 1 Gabs Enzymes and other things are used to loosed up the chromatin can use covalent chemistry to do so ATP hydrolysis acts as an elongation factor allowing RNA polymerase to move along chromatin It takes ATP to move DNA RNA add nucleotides RNA transcription stops at a speci c DNA sequence prokaryotes and a polyadenylation signal eukaryotes Most eukaryotic RNA requires post transcriptional processing before it can be functional mRNA messenger RNA processing Only happens in eukaryotes RNA that is to be used for protein encoding needs a lot of post transcriptional processing before it is ready to be called mRNA 5 end of RNA is rst to be processed occurs as soon as it exits RNA polymerase 7 methylguanosine cap is added indicating that RNA is to become mRNA Cap shows things that the RNA is a full length RNA with all of the necessary information Pre mRNA processing Most genes for protein coding contain introns intervening sequences which interrupt the coding sequence making it unusable Exons are expressed sequences Introns get cut out exons are kept in Introns are removed by RNA splicing Done by spliceosomes Spilceosomes assemble on pre mRNA while it is still undergoing transcription but may not begin splicing immediately Splicing can be done many different ways depending on the pre mRNA Are made up of small ribonucleoproteins snRPS which are made up small nuclear RNAs snRNAs and multiple proteins 2 Gabs 3 end gets a poly A tail when transcription is done and RNA is released from RNA polymerase original 3 end is cleaved off and a series of approximately 200 nucleotides of A s are added by poly A polymerase This shows cell that it is an intact RNA sequence Poly A proteins bind to the tail which is important for later protein synthesis and the export of mRNA from the nucleus mRNA export Up to this point the RNA has remained in the nucleus It is now ready to go into the cytosol to take part in protein synthesis Before export some things must be altered Nuclear export receptor the mature mRNA binds to this which guides it through the nuclear pore complex into the cytosol Most RNA in a cell is rRNA involved with ribosomes rRNA is synthesized using RNA polymerase 1 and 3 Mostly altered in nucleolus Some other RNAs snRNA snoRNA tRNA siRNA miRNA to name a few mature RNA which has been exported to cytosol can translated into protein by Protein Translation ribosome transcription DNA RNA 1 1 subunit correspondence same language different medium U instead of T and ribose instead of deoxyribose translation RNA protein not 1 1 there are 20 amino acids and only 4 bases different chemical language to accommodate 20 different amino acids code must be 3 nucleotides which results in 64 nucleotide combination set of 3 nucleotides is called a codon each amino acid had multiple codons 3 Gabs lucine is the most abundant amino acid has the most codons methyanine AUG stop codons UAA UAG UGA transfer RNA tRNA an intermediary matches amino acids with codons as the amino acid cannot directly interact with the RNA tRNA are short RNAs distinctive 3D structure attaches to amino acids with 3 end with the help of aminoacyl tRNS synthase each amino acid has its own snythase has anticodons amino acid is activated by AMP before transfer to tRNA synthetase checks for accuracy when complete protein synthesis goes from N terminal to C terminal new amino acid is added to C terminal in a growing chain last tRNA attached has a peptide chain aminoacyl tRNA replaces old tRNA extending the chain by one residue ribosome decodes RNA message reads mRNA 5 to 3 reads 1 codon at a time AUG indicates where translation is to begin stops at stop codon release factor a protein binds to ribosome at stop codons allow water to get between tRNA and polypeptide chain which releases the complete protein ribosome dissociates into subunits releasing mRNA remaining tRNA and release factor Protein translation occurs on polyribosomes one ribosome can only make one peptide chain at a time however cells need a lot of peptide chains so ribosomes can produce multiple peptide chains at a time as soon as one peptide chain is far enough along the ribosome the production of another begins a polyribosome is one which has multiple ribosomes translating the mRNA Antibiotics and protein synthesis 4 Gabs many important antibiotics are protein synthesis inhibitors in protein synthesis some toxins can inhibit protein systems most only effect prokaryotes the ribosomes are different in prokaryotes and eukaryotes can also affect ribosomes in chloroplasts and mitochondria which are similar some can block ribosomes in eukaryotes cyclohexamide only blocks translocation reactions in eukaryotes puromycin causes premature termination in eukaryotes and prokaryotes of growing peptide chain by mimicking aminoacyl tRNA Protein and RNA sythesis takes a lot of energy each level of production has different content 5
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