Biology 151 1st Edition Lecture 12 Outline of Last Lecture 1. What is a gene?2. What do genes on DNA do?3. Beadle and Tatum (1941)4. How does DNA make a protein?5. Ribosomes and Ribosomal RNA (rRNA)6. Structure of RNA7. Ribosomes are the sites of protein synthesis8. RNA9. Transcription of RNA from DNA template10. RNA polymerase11. Messenger RNA (mRNA) carries info. from DNA to ribosomeOutline of Current Lecture 1. Transcription by RNA polymerase2. What's the code? DNA sequence contains code for linking amino acids into protein3. At ribosome4. Is it a nucleic acid?5. How do you bind all 64 codons?6. Summary - the roles of RNA in translation7. Starting and stopping translation: Starting translation in correct reading frame8. Stopping translation9. mRNA can have 5' and 3' un-translated regions10. In prokaryotes one mRNA can code for several different proteinsCurrent Lecture - 2/16/15- transcription - DNA template to RNA by RNA polymeraseTranscription by RNA polymerase:- like DNA polymerase except...- made of 12 different proteins- builds single stranded complementary RNA from DNA template- does not require primer- only parts of the DNA are used as templates- RNA uses U instead of T- temporarily separates DNA strands, RNA detaches from templateWhat's the code? DNA sequence contains code for linking amino acids into protein:- code has to contain at least 3 bases per amino acid to get 20 amino acids from 4 nucleotides- decoded by synthesizing different DNA and RNA molecules, seeing what proteins producedThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- early amino acid (AA) coded by nucleotide triplet codon in mRNA (or non-template strand of DNA) - DNA sequence on one strand- genetic code (U=T) with 3 nucleotide "codon" triplets- methionine is start codon = AUG (ATG) - start translation- stop codons tell you where to stop translation- ribosome moves from 5' to 3' on mRNA = protein: amino (made first) to carboxyl (made last)At ribosome:- 1) RNA- 2) mRNA- 3) Adaptors for translation of mRNA into protein- Crick's hypothesis - "adaptor" matches specific amino acids with specific mRNA triplet codons- maybe the adaptor binds mRNA using base pairing?Is it a nucleic acid?:- adaptors = transfer RNAs- small, stable RNAs, 70-80 nucleotides- each type of tRNA binds a specific type of amino acid- anticodon - complementary to nucleotides in mRNA- ribosome links amino acids attached to tRNAs into protein chain- how does each tRNA get its amino acid?-aminocyl tRNA synthetases (different ones for each type of tRNA)-specific aminoacyl tRNA synthase uses ATP energy to attach specific amino acid to specific tRNA- each type of tRNA has a different 3 nucleotide "anticodon" that binds to specific 3 nucleotide codon in mRNA - runs in antiparallel direction- ribosome links amino acids attached to tRNAs into protein chain- between 20 and 61 kinds of tRNAs in a cellHow do you bind all 64 codons?:- "wobble" base doesn't have to be an exact match for mRNA -some tRNAs will bind to more than one codon-assume matching between codons and anticodons is correctSummary - the roles of RNA in translation:- ribosomal RNAs (with proteins) make the ribosome = the "machine" for making proteins- messenger RNA codons translated into protein at ribosome- transfer RNA - brings amino acids to ribosome - each tRNA carries a specific amino acid- each has a specific anticodon that binds to mRNA codonStarting and stopping translation: starting translation in correct reading frame:- RNA: 3 frames 5' to 3'- DNA: 6 frames, 3 forward and 3 reverse compliments - one "start" and 3 "stop" codonsStarting translation:- AUG = start codon, matching initiator tRNA, binds amino acid methionine (or fMet in bacteria)- mRNA and initiator tRNA bind: small ribosomal subunits, recruits large subunitStopping translation: - translation stops at one of three "nonsense" stop codons- binds release factor (protein, not tRNA), which releases polypeptidemRNA can have 5' and 3' un-translated regions:- only translate portion between start and stop codons- the 2 ends of an mRNA are often un-translated regions - eukaryotes: usually one protein-coding segment per mRNA (some with alternative start codons, rarely with multiple starts/stops)In prokaryotes some mRNA can code for several consecutive proteins:- prokaryotes: single mRNA can have several consecutive start-stop intervals = operon- translation by ribosomes to make different
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