MCB 100 1st Edition Lecture 21 Outline of Last Lecture I. DNA replicationII. TranscriptionIII. Three major types of RNAOutline of Current Lecture I. Protein synthesis by ribosomes- translationII. Fundamental properties of the genetic code III. Viral variations of the central dogma Current LectureI. Protein synthesis by ribosomes- translationa. Review: ribosome = complex enzyme made of rRNA molecules and 50 different proteins; reads information in mRNA and use tRNA molecules to assemble an amino acid chain following instructions in mRNA chain b. Translation = process of protein synthesis by ribosomesi. Ribosome moves along mRNA reading the codons and adding 1 amino acid to the growing peptide chain for each codon ii. Movement of ribosome = from 5' to 3' end with small subunits of ribosome iii. Anticodon = sequence of 3 nucleotides in tRNA molecule that is complementary to a codon (the matching of compatible anticodon to a codon makes sure that the right amino acid will be inserted into the protein iv. The genetic code = needed for translating information that is contained within a nucleic acid sequence into information that is in the form of a protein sequence1. 64 codons 2. Start codon = AUG (tells ribosome where to begin translation; near the ribosome binding site)3. Stop codon = UAA, UAG, UGA (tells ribosome to stop adding on to proteinchain because its finished) II. Fundamental properties of the genetic code a. Universal; same for all living organisms (with a few exceptions) b. Also called a triplet code- takes 3 base pairs of DNA to contain the information needed to specify the use of one amino acid in a protein (codon is 3 bases of mRNA) c. 64 codons in the genetic code These 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.i. 61 are sense codons- they direct the incorporation of specific amino acids into a growing protein chainii. 3 are nonsense codons- terminates translation b. Ambiguous- there is only 1 amino acid that a particular codon will specify! (CUU encodes Leucine always) c. Said to be degenerate- most amino acids can be specified for by more than one codon (ex. UUA UUG CUU CUC CUA CUG => all specify Leucine; but methionine is always specified by AUG codon and tryptophan is always specified by UGG; internal AUG codons encode methionine in Bacteria and Eukaryotes) d. Not punctuated- there are no commas, periods, or semicolonse. Instructions for (where should RNA polymerase begin transcribing DNA, what in the AUG in mRNA is the real translation start site, where does RNA polymerase stop transcription, and other necessary signals) are sequences of nucleotides that are often found near structural genes II. Viral variations of the central dogmaa. Viruses with RNA genomesi. + strand RNA viruses (ex. Picornaviruses- polio and rhinoviruses)ii. - strand RNA viruses (ex. Orthomyxoviruses- influenza) iii. Positive-sense viral RNA is identical to viral mRNA --> can be translated directlyby host cell's ribosomes iv. Negative-sense viral RNA is complementary to mRNA--> must be copied by RNA-dependent RNA polymerase to make a positive-sense mRNA before translation v. dsRNA viruses (ex. Reoviruses- rotovirus)vi. Retroviruses (ex. HIV) vii. Viruses with ssDNA genomes (ex. Parvovirus) b. Genome of a single stranded RNA virus must be copied by RNA-dependent RNA polymerasec. Retrovirus RNA is copied by reverse transcriptase to make a DNA copy of the RNA genetic
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