Lecture 23 Outline of Last Lecture I. CancerII. Oncogenes and Proto-OncogenesIII. Tumor-Suppressor GenesIV. MicroRNAsOutline of Current Lecture I. From Gene to ProteinII. MutationsIII. Split-Genes and RNA ProcessingIV. MicroRNAs and Gene ExpressionV. Microbiology of CancerVI. Genetics of VirusesCurrent LectureOverview of Material Covered Post-Exam 3I. Chapter 17 (Lecture 21): From Gene to Protein1) What is the central dogma of molecular biology? Define the terms transcription and translation.The “central dogma of molecular biology” is the making of proteins. Transcription is the synthesis of RNA from a DNA template. Translation is the synthesis of proteins using information in the mRNA molecule.2) Define the terms for transcription.Promoter: the place where the RNA polymerase binds to on the DNA at the beginning of a geneRNA Polymerase: the enzyme that makes RNA BIOL 1st EditionTranscription Factor: the special proteins that guide the RNA polymerase to the promoterTerminator: the place where transcription stops where the RNA polymerase releases the finished mRNA molecule, and then falls off the DNA3) Define the terms for translation.mRNA: RNA molecule that carries the coding information; a series of codons that must be decoded, one right after the other, made of G, C, U, and ACodon: each 3-nucleotide code word that codes for some particular amino acid; a sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA moleculeReading Frame: a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) moleculeinto a set of consecutive, non-overlapping tripletsStop Codon: don’t code for anything, but are signals to stop translationtRNA: functions as a “decoder” that pairs the right amino acid with its codonAnticodon: a sequence of three nucleotides forming a unit of genetic code in a tRNA molecule, corresponding to a complementary codon in messenger RNA.Ribosome (small and large subunits): organelle that coordinates the pairing of tRNAs with their mRNA codons; separate except when translating mRNA into protein; small binds to mRNA and special tRNA; large binds to initiator tRNA in the “P-site”P-site: large subunit of ribosome binds with initiator tRNA in the “P-site”; functioning ribosomeA-site: a tRNA with correct anticodon for the next codon (one after the start codon)Release Factor: binds in the a-site; this releases the protein; ribosome separates into subunits ready to translate next mRNA4) What are the mRNA structure terms? Define them. 5’ Cap: the cap that functions as a way for ribosomes to know where to attach5’ Untranslated Region: the region between 5’ cap and the “start codon”3’ Untranslated Region: the region between the “stop codon” and the 3’ endPoly-A Tail: attached to the 3’ untranslated region; stabilizes mRNA and regulates translation5) Understand the sequence of events, and briefly what happens during initiation, elongation and termination of translation (movie)Sequence: Initiation, Elongation, TerminationInitiation: small ribosomal subunit is base-paired to an initiator tRNA and moves to the initiation site; large ribosomal subunit attaches to the tRNA, which is attached to the small ribosomal unit, creating the p-siteElongation: a second tRNA enters the a-site bonded with a peptide bond to the first tRNA; the methionine is transferred to the a-site amino acid; the first tRNA exits, the third tRNA enters, and the second tRNA moves along, etc.Termination: when a stop codon is encountered, a release factor enters the a-site, and translation is terminated; the newly formed protein detaches, and the ribosome separates into subunits ready to translate again6) Given a codon, determine the anticodon of the tRNA that would bind to it.Base-pairing rules for mRNA codons to tRNA: U to A, A to U; C to G, G to CExample: Given  5’ – AUG – 3’, the anticodon would be: 3’ – UAC – 5’II. Mutations (Lecture 21)7) What is a mutation?Mutations are changes in the nucleotide sequence in DNA.8) Name two basic classes of mutation.The two basic classes of mutations are base-pair substitutions and insertions/deletions.Base-pair substitutions occur when a nucleotide pair is replaced by another. Insertions/deletions occur when one or more nucleotide pairs are inserted or deleted from a gene.9) What is a missense mutation? What is a nonsense mutation? Which of these is generally more serious?A missense mutation alters a codon in a gene, but the new codon still codes for an amino acid. Depending on how different the new amino acid is and where it is located determines whether this mutation is lethal or harmless.A nonsense mutation is when a codon is changed into a “stop codon”, which stops translation prematurely. Nonsense mutations are significantly more serious because they prematurely stop translation from occurring.10) What is a frameshift mutation?A “frameshift mutation” occurs when the number of nucleotides inserted or deleted is in multiples of 3.III. Split Genes and RNA Processing (Lecture 21)11) Is most DNA in eukaryotes coding or non-coding?Most DNA in eukaryotes is non-coding.12) What is an exon? What is an intron?An exon is a coding region within the DNA that carries the code for how to make a protein.An intron is a non-coding region within the DNA that does not encode a protein.13) What happens during RNA splicing? What is the name of the complex particles that carry out RNA splicing? Where in the cell does RNA splicing occur?RNA splicing occurs after transcription, and it is the process of removing the introns from the mRNA and hooking the exons back together. “Spliceosomes” carry out the process of RNA splicing.RNA splicing occurs in the nucleus of a cell.14) Name three processing steps that must occur to produce the mature mRNA from a gene that has introns.The three processing steps that must occur to produce the mature mRNA from a gene that has introns are RNA splicing, the addition of a 5’ cap, and the addition of a 3’ poly-A tail.IV. MicroRNAs and Gene Expression (Lecture 21)15) What is meant by gene expression? “Gene expression” or “expressed genes” are when a gene is actively being used to make proteins (through transcription and then translation). 16) What is meant by “transcriptional control” and “post-transcriptional control”?Transcriptional control is the control of gene expression by determining which genes are transcribed, when