BIOL 1441 1st Edition Lecture 30 Outline of Last Lecture I. DNA replication modelII. DNA replicationIII. Repairing DNAOutline of Current Lecture I. Flow of Genetic InformationII. Genetic CodeIII. TranscriptionIV. TranslationV. Completing the functional proteinVI. Point mutationsCurrent LectureI. Flow of Genetic Informationa. Proteins link between genotype & phenotypeb. Gene expression- process by which DNA directs synthesis of proteinsc. Gene expression occurs in 2 stages:i. Transcription- copy DNA 1. Copying (transcribing) DNA into RNA2. Transcript (the copy) is mRNA- messenger RNAa. Carries the message from DNA to protein-synthesizing machineryb. rRNA- ribosomal RNA, tRNA- transfer RNA3. Eukaryotes transcription occurs in nucleus4. Prokaryotes occurs in cytosol- there is no nucleusii. Translation- make protein1. Synthesize protein from mRNAThese 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.a. Translated from nucleic acid into a protein2. Site of translation- ribosomes in cytosola. For both eukaryotes AND prokaryotes!b. Facilitate linking of amino acids into polypeptide chainsd. Genes specify Proteinsi. One gene- usually encodes one protein1. Many proteins made of several polypeptide chains- several genes encode themii. DNA splicing- one gene can make splice variants of a proteiniii. Some genes encode RNA, not proteinsiv. Prokaryotes- translation occurs in cytoplasm1. Very efficient and quickII. Genetic Code: Codons a. Codons- triplets of bases (3 DNA bases)b. Read in the 5¢ to 3¢ directionc. Each codon specifies an amino acidi. ATG- methionineii. CCC- prolineiii. AGU- serined. 64 total codons- 61 code for amino acids, 3 stop codonse. Degenerative code- some amino acids have more than one codei. Allows room for error, “wobble room”ii. 3rd position- switch base, still the same amino acidf. No codon specifies more than one amino acidg. Reading Framei. Codons must be read in the correct reading frame (correct groupings) in order for the specified polypeptide to be produced1. The red dog ate the bug.2. T her edd oga tet thb ug.h. Nearly universal, shared by the simplest bacteria to the most complex animalsi. Genes can be transcribed and translated after being transplanted from one species to anotherj. Bacteria used to make human proteins- insulin and growth hormoneIII. Transcription- Copying DNA into RNAa. RNA synthesis follows the same base-pairing rules as DNA, except uracil substitutes for thyminei. A – Uii. C – Gb. Synthesized in 5’ – 3’ directionc. No primer is needed (in DNA replication, DNA polymerase needs a primer)d. RNA Polymerase- binds promoter, unwinds DNA strands & polymerizes RNA nucleotidese. Promoter Sequencei. Promoter- DNA sequence where RNA polymerase attaches and begins transcription1. “on switch” f. RNA Polymerasei. Prokaryotes- one type RNA polymeraseii. Eukaryotes- 3 types of RNA polymerase1. RNA polymerase I, II, III2. RNA pol II- synthesizes mRNAg. The three stages of transcription:i. Initiation: RNA pol binds promotor, DNA strands unwind, initiates RNA synthesisii. Elongation: RNA polymerase moves downstream, unwinding DNA and elongating the RNA transcript in 5’-3’ directioniii. Termination: RNA transcript is complete and is released as RNA polymerase detaches from the RNAh. Initiation of transcriptioni. Promoters signal the initiation of RNA synthesis1. Upstream from start siteii. Prokaryotes- RNA pol II binds directly to promoteriii. Eukaryotes- transcription factors must be presenti. Transcription Factors- eukaryotesi. Proteins that mediate the binding of RNA polymerase & initiation of transcriptionii. Transcription Initiation Complex- completed assembly of transcription factors & RNA polymerase II bound to a promoteriii. TATA box- promoter crucial in forming the initiation complex in eukaryotesj. Elongation of the RNA Strandi. RNA polymerase moves along DNA- untwists double helix 10 - 20 bases ata time1. Transcription rate- 50- 60 nucleotides/sec (eukaryotes)ii. One gene can be transcribed simultaneously by several RNA polymerases-make lots of proteink. Transcription Termination - Prokaryotesi. RNA polymerase stops transcription at the end of the terminator (stop sequence)ii. RNA terminator sequence that is copied causes RNA polymerase to detach & release the transcriptiii. mRNA transcript is immediately translated into proteinl. Transcription Termination - Eukaryotesi. RNA polymerase transcribes polyadenylation signal sequence (AAUAAA) ii. 10-35 nucleotides downstream from AAUAAA signal, pre-mRNA transcriptis cut from polymeraseiii. RNA polymerase eventually falls off the DNAm. RNA Processing- Eukaryotesi. Pre-mRNA modified into mRNA before it leaves the nucleus- RNA processingii. Both ends of the primary transcript are altered1. 5’ cap2. 3’ tailiii. Interior parts (non-coding regions- introns) cut out, other parts spliced back togethern. Alteration of mRNA Endsi. 5¢ cap- modified form of guanine, inserted backwardsii. 3¢ end- poly-A tail, 50-250 adenine nucleotideso. Function of modifications:i. Facilitate the export of mRNA from nucleusii. Protect mRNA from hydrolytic enzymesiii. Help ribosomes attach to the 5’ end once in cytoplasmp. RNA Splicingi. Eukaryotic have long non-coding stretches of nucleotides in between coding regionsii. Introns- noncoding regions, intervening sequencesiii. Exons- coding regions, translated & expressediv. RNA splicing- removes introns & joins exons, creating mRNA molecule with a continuous coding sequenceq. Ribozymesi. RNA that functions as enzymes that splice RNA ii. Intron functions as a ribozyme, splices itself outiii. Discovery of ribozymes shattered the belief that all biological catalysts r. Alternative RNA Splicingi. Some genes can encode more than one kind of polypeptideii. Depends on which segments are treated as exons during RNA splicingiii. Alternative splicing allows an organism to produce a much greater number of different proteins than its number of genesIV. TRANSLATIONa. key playersi. mRNA translated into proteinii. rRNA- ribosomal RNA- makes up ribosomes1. Ribosome- couples mRNA with tRNAiii. tRNA- transfer RNA- carry (transfers) amino acids to ribosomeb. tRNAi. Transfers amino acids from cytoplasm to ribosomeii. One tRNA for each amino acidiii. Cell keeps cytoplasm stocked with tRNAs bound to amino acidsiv. Each tRNA carries a specific amino acid on one endv.