BIOL 1441 1st Edition Lecture 30 Outline of Last Lecture I DNA replication model II DNA replication III Repairing DNA Outline of Current Lecture I Flow of Genetic Information II Genetic Code III Transcription IV Translation V Completing the functional protein VI Point mutations Current Lecture I Flow of Genetic Information a Proteins link between genotype phenotype b Gene expression process by which DNA directs synthesis of proteins c Gene expression occurs in 2 stages i Transcription copy DNA 1 Copying transcribing DNA into RNA 2 Transcript the copy is mRNA messenger RNA a Carries the message from DNA to protein synthesizing machinery b rRNA ribosomal RNA tRNA transfer RNA 3 Eukaryotes transcription occurs in nucleus 4 Prokaryotes occurs in cytosol there is no nucleus ii Translation make protein 1 Synthesize protein from mRNA 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 II III a Translated from nucleic acid into a protein 2 Site of translation ribosomes in cytosol a For both eukaryotes AND prokaryotes b Facilitate linking of amino acids into polypeptide chains d Genes specify Proteins i One gene usually encodes one protein 1 Many proteins made of several polypeptide chains several genes encode them ii DNA splicing one gene can make splice variants of a protein iii Some genes encode RNA not proteins iv Prokaryotes translation occurs in cytoplasm 1 Very efficient and quick Genetic Code Codons a Codons triplets of bases 3 DNA bases b Read in the 5 to 3 direction c Each codon specifies an amino acid i ATG methionine ii CCC proline iii AGU serine d 64 total codons 61 code for amino acids 3 stop codons e Degenerative code some amino acids have more than one code i Allows room for error wobble room ii 3rd position switch base still the same amino acid f No codon specifies more than one amino acid g Reading Frame i Codons must be read in the correct reading frame correct groupings in order for the specified polypeptide to be produced 1 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 animals i Genes can be transcribed and translated after being transplanted from one species to another j Bacteria used to make human proteins insulin and growth hormone Transcription Copying DNA into RNA a RNA synthesis follows the same base pairing rules as DNA except uracil substitutes for thymine i A U ii C G b Synthesized in 5 3 direction c No primer is needed in DNA replication DNA polymerase needs a primer d RNA Polymerase binds promoter unwinds DNA strands polymerizes RNA nucleotides e Promoter Sequence i Promoter DNA sequence where RNA polymerase attaches and begins transcription 1 on switch f RNA Polymerase i Prokaryotes one type RNA polymerase ii Eukaryotes 3 types of RNA polymerase 1 RNA polymerase I II III 2 RNA pol II synthesizes mRNA g The three stages of transcription i Initiation RNA pol binds promotor DNA strands unwind initiates RNA synthesis ii Elongation RNA polymerase moves downstream unwinding DNA and elongating the RNA transcript in 5 3 direction iii Termination RNA transcript is complete and is released as RNA polymerase detaches from the RNA h Initiation of transcription i Promoters signal the initiation of RNA synthesis 1 Upstream from start site ii Prokaryotes RNA pol II binds directly to promoter iii Eukaryotes transcription factors must be present i Transcription Factors eukaryotes i Proteins that mediate the binding of RNA polymerase initiation of transcription ii Transcription Initiation Complex completed assembly of transcription factors RNA polymerase II bound to a promoter iii TATA box promoter crucial in forming the initiation complex in eukaryotes j Elongation of the RNA Strand i RNA polymerase moves along DNA untwists double helix 10 20 bases at a time 1 Transcription rate 50 60 nucleotides sec eukaryotes ii One gene can be transcribed simultaneously by several RNA polymerasesmake lots of protein k Transcription Termination Prokaryotes i 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 transcript iii mRNA transcript is immediately translated into protein l Transcription Termination Eukaryotes i RNA polymerase transcribes polyadenylation signal sequence AAUAAA ii 10 35 nucleotides downstream from AAUAAA signal pre mRNA transcript is cut from polymerase IV iii RNA polymerase eventually falls off the DNA m RNA Processing Eukaryotes i Pre mRNA modified into mRNA before it leaves the nucleus RNA processing ii Both ends of the primary transcript are altered 1 5 cap 2 3 tail iii Interior parts non coding regions introns cut out other parts spliced back together n Alteration of mRNA Ends i 5 cap modified form of guanine inserted backwards ii 3 end poly A tail 50 250 adenine nucleotides o Function of modifications i Facilitate the export of mRNA from nucleus ii Protect mRNA from hydrolytic enzymes iii Help ribosomes attach to the 5 end once in cytoplasm p RNA Splicing i Eukaryotic have long non coding stretches of nucleotides in between coding regions ii Introns noncoding regions intervening sequences iii Exons coding regions translated expressed iv RNA splicing removes introns joins exons creating mRNA molecule with a continuous coding sequence q Ribozymes i RNA that functions as enzymes that splice RNA ii Intron functions as a ribozyme splices itself out iii Discovery of ribozymes shattered the belief that all biological catalysts r Alternative RNA Splicing i Some genes can encode more than one kind of polypeptide ii Depends on which segments are treated as exons during RNA splicing iii Alternative splicing allows an organism to produce a much greater number of different proteins than its number of genes TRANSLATION a key players i mRNA translated into protein ii rRNA ribosomal RNA makes up ribosomes 1 Ribosome couples mRNA with tRNA iii tRNA transfer RNA carry transfers amino acids to ribosome b tRNA i Transfers amino acids from cytoplasm to ribosome ii One tRNA for each amino acid iii Cell keeps cytoplasm stocked with tRNAs bound to amino acids iv Each tRNA carries a specific amino acid on one end v Anticodon on the other end base pairs with a complementary codon on mRNA vi Structure Function of tRNA 1 Single RNA strand 80 nucleotides long vii tRNA binds a specific amino acid