BIOLOGY 101 CHAPTER 17: Gene Expressin: Frm Gene t Prtein
Gene Expressin: Frm Gene t Prtein: CONCEPTS: 17.1 Genes specify prteins via transcriptin and translatin 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk 17.3 Eukarytic cells mdify RNA after transcriptin 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin The infrmatin cntent f genes is in the specific sequences f nucletides The DNA inherited by an rganism leads t specific traits by dictating the synthesis f prteins Prteins are the links between gentype and phentype Gene expressin, the prcess by which DNA directs prtein synthesis, includes tw stages: transcriptin and translatin
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Genetic infrmatin fr building prteins is cntained the genes f DNA Genes can t leave the nucleus, s a messenger is needed t carry the infrmatin in DNA t the cytplasm (where prteins are synthesized) mrna is a cpy f a gene that can leave the nucleus and enter the cytplasm In the cytplasm, infrmatin in mrna is used t assemble amin acids int prteins
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin RNA is the bridge between genes and the prteins fr which they cde Transcriptin is the synthesis f RNA using infrmatin frm DNA Transcriptin prduces messenger RNA (mrna) mrna is a cpy f a gene that can leave the nucleus Translatin is the synthesis f a plypeptide, using infrmatin in the mrna Ribsmes are the rganelles that read mrna t prduce prteins
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin In prkarytes, translatin f mrna can begin befre transcriptin has finished In a eukarytic cell, the nuclear envelpe separates transcriptin frm translatin Eukarytic RNA transcripts are mdified thrugh RNA prcessing t yield the finished mrna
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin In prkarytes, translatin f mrna can begin befre transcriptin has finished In a eukarytic cell, the nuclear envelpe separates transcriptin frm translatin Eukarytic RNA transcripts are mdified thrugh RNA prcessing t yield the finished mrna
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin In prkarytes, translatin f mrna can begin befre transcriptin has finished In a eukarytic cell, the nuclear envelpe separates transcriptin frm translatin Eukarytic RNA transcripts are mdified thrugh RNA prcessing t yield the finished mrna
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin In prkarytes, translatin f mrna can begin befre transcriptin has finished In a eukarytic cell, the nuclear envelpe separates transcriptin frm translatin Withut a nucleus, pst-transcriptinal mrna mdificatin wuld nt be pssible
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin The Central Dgma is the cncept that cells are gverned by a cellular chain f cmmand: DNA RNA prtein
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin TRANSCRIPTION: 1) One strand f a gene is transcribed int (cpied) int mrna mrna is simply a cpy f a gene it is cmplementary t the cded DNA infrmatin RNA plymerase adds RNA nucletides t a grwing mrna using ne DNA strand as a template A primary transcript is the initial RNA transcript frm any gene prir t prcessing
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin RNA PROCESSING: 2) In Eukarytes the primary transcript is mdified befre it leaves the nucleus and travels t the cytplasm Sme prtins f the primary transcript are remved prir t leaving the nucleus The final mrna transcript then leaves the nucleus and enters the cytplasm
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Basic Principles f Transcriptin and Translatin TRANSLATION: 3) Ribsmes assemble prteins by hking the apprpriate amin acids tgether In the cytplasm, Ribsmes attach t the mrna transcript Ribsmes are rganelles that can read the genetic cde The cde is used by ribsmes t select specific amin acids Ribsmes assemble prteins by hking the apprpriate amin acids tgether
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Q: Hw is the mrna cde interpreted by ribsmes?
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Q: Hw is the mrna cde interpreted by ribsmes? Cdns: Triplets f Nucletides The flw f infrmatin frm gene t prtein is based n a triplet cde: a series f nnverlapping, three-nucletide sequences called cdns During translatin, the cdns are read in the 5 3 directin Each cdn specifies the amin acid (ne f 20) t be placed at the crrespnding psitin alng a plypeptide
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Cdns: Triplets f Nucletides There are 64 (r 4 3 ) pssible cdns that cde fr each f the 20 amin acids Of the 64 triplets, 61 cde fr amin acids; 3 triplets are stp signals t end translatin The genetic cde is redundant (mre than ne cdn may specify a particular amin acid) but nt ambiguus; n cdn specifies mre than ne amin acid Cdns must be read in the crrect reading frame (crrect grupings) in rder fr the specified plypeptide t be prduced
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Cdns: Triplets f Nucletides There are 64 (r 4 3 ) pssible cdns that cde fr each f the 20 amin acids Of the 64 triplets, 61 cde fr amin acids; 3 triplets are stp signals t end translatin The genetic cde is redundant (mre than ne cdn may specify a particular amin acid) but nt ambiguus; n cdn specifies mre than ne amin acid Cdns must be read in the crrect reading frame (crrect grupings) in rder fr the specified plypeptide t be prduced
Gene Expressin: Frm Gene t Prtein: 17.1 Genes specify prteins via transcriptin and translatin Evlutin f the Genetic Cde The genetic cde is nearly universal, shared by the simplest bacteria t the mst cmplex animals Genes can be transcribed and translated after being transplanted frm ne species t anther
Gene Expressin: Frm Gene t Prtein: 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk Mlecular prcess f Transcriptin: RNA Plymerase reads the DNA template strand and adds cmplementary RNA nucletides t a grwing mrna chain The DNA sequence where RNA plymerase attaches is called the prmter The stretch f DNA that is transcribed is called a transcriptin unit
Gene Expressin: Frm Gene t Prtein: 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk Mlecular prcess f Transcriptin: The three stages f transcriptin Initiatin Elngatin Terminatin
Gene Expressin: Frm Gene t Prtein: 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk Mlecular prcess f Transcriptin: INITIATION OF TRANSCRIPTION Prmters are DNA sequences that signal the transcriptinal start pint and usually extend several dzen nucletide pairs upstream f the start pint Transcriptin factrs mediate the binding f RNA plymerase and the initiatin f transcriptin A prmter called a TATA bx is crucial in frming the initiatin cmplex in eukarytes
Gene Expressin: Frm Gene t Prtein: 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk Mlecular prcess f Transcriptin: INITIATION OF TRANSCRIPTION Prmters are DNA sequences that signal the transcriptinal start pint and usually extend several dzen nucletide pairs upstream f the start pint Transcriptin factrs mediate the binding f RNA plymerase and the initiatin f transcriptin A prmter called a TATA bx is crucial in frming the initiatin cmplex in eukarytes
Gene Expressin: Frm Gene t Prtein: 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk Mlecular prcess f Transcriptin: ELONGATION OF TRANSCRIPTION As RNA plymerase mves alng the DNA, it untwists the duble helix, 10 t 20 bases at a time A gene can be transcribed simultaneusly by several RNA plymerases Nucletides are added t the 3 end f the grwing RNA mlecule
Gene Expressin: Frm Gene t Prtein: 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk Mlecular prcess f Transcriptin: ELONGATION OF TRANSCRIPTION As RNA plymerase mves alng the DNA, it untwists the duble helix, 10 t 20 bases at a time A gene can be transcribed simultaneusly by several RNA plymerases Nucletides are added t the 3 end f the grwing RNA mlecule
Gene Expressin: Frm Gene t Prtein: 17.2 Transcriptin is the DNA-directed synthesis f RNA: a clser lk Mlecular prcess f Transcriptin: TERMINATION OF TRANSCRIPTION In eukarytes, RNA plymerase II transcribes the plyadenylatin signal sequence This sequence signals the additin f a ply-a tail during mrna prcessing The RNA transcript is released 10 35 nucletides past this plyadenylatin sequence
Gene Expressin: Frm Gene t Prtein: 17.3 Eukarytic cells mdify RNA after transcriptin RNA PROCESSING: Enzymes in the eukarytic nucleus mdify pre-mrna (RNA prcessing) befre the genetic messages are dispatched t the cytplasm During RNA prcessing, bth ends f the primary transcript are usually altered Als, usually certain interir sectins f the mlecule are cut ut, and the remaining parts spliced tgether
Gene Expressin: Frm Gene t Prtein: 17.3 Eukarytic cells mdify RNA after transcriptin Alteratin f mrna Ends: Each end f a pre-mrna mlecule is mdified in a particular way The 5 end receives a mdified nucletide 5 cap The 3 end gets a ply-a tail These mdificatins share several functins They seem t facilitate the exprt f mrna t the cytplasm They prtect mrna frm hydrlytic enzymes They help ribsmes attach t the 5 end
Gene Expressin: Frm Gene t Prtein: 17.3 Eukarytic cells mdify RNA after transcriptin Split Genes and RNA Splicing: Mst eukarytic genes and their RNA transcripts have lng nncding stretches f nucletides that lie between cding regins These nncding regins are called intervening sequences, r intrns The ther regins are called exns because they are eventually expressed, usually translated int amin acid sequences RNA splicing remves intrns and jins exns, creating an mrna mlecule with a cntinuus cding sequence
Gene Expressin: Frm Gene t Prtein: 17.3 Eukarytic cells mdify RNA after transcriptin Split Genes and RNA Splicing: Mst eukarytic genes and their RNA transcripts have lng nncding stretches f nucletides that lie between cding regins These nncding regins are called intervening sequences, r intrns The ther regins are called exns because they are eventually expressed, usually translated int amin acid sequences This creates different versins f genes! At times, the exns may be changed
Gene Expressin: Frm Gene t Prtein: 17.3 Eukarytic cells mdify RNA after transcriptin Ribzymes: Ribzymes are catalytic RNA mlecules that functin as enzymes and can splice RNA The discvery f ribzymes rendered bslete the belief that all bilgical catalysts were prteins Three prperties f RNA enable it t functin as an enzyme 1. It can frm a three-dimensinal structure because f its ability t base-pair with itself 2. Sme bases in RNA cntain functinal grups that may participate in catalysis 3. RNA may hydrgen-bnd with ther nucleic acid mlecules
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk Genetic infrmatin flws frm mrna t prtein thrugh the prcess f translatin
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk Mlecular Cmpnents f Translatin: A cell translates an mrna message int prtein with the help f transfer RNA (trna) trnas transfer amin acids t the grwing plypeptide in a ribsme trna s each carry different amin acids, and each trna has an Anticdn, that is the cmplementary sequence t a cdn This is hw trnas knw when they are needed. The ribsme will expse the cdn and the apprpriate trna will bring in its crrespnding amin acid
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk Mlecular Cmpnents f Translatin: A cell translates an mrna message int prtein with the help f transfer RNA (trna) trnas transfer amin acids t the grwing plypeptide in a ribsme trna s each carry different amin acids, and each trna has an Anticdn, that is the cmplementary sequence t a cdn This is hw trnas knw when they are needed. The ribsme will expse the cdn and the apprpriate trna will bring in its crrespnding amin acid
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk RIBOSOMES: Ribsmes facilitate specific cupling f trna anticdns with mrna cdns in prtein synthesis The tw ribsmal subunits (large and small) are made f prteins and ribsmal RNA (rrna)
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk RIBOSOMES: A ribsme has three binding sites fr trna The A site hlds the trna that carries the next amin acid t be added t the chain amin acids enter here The P site hlds the trna that carries the grwing plypeptide chain The E site is the exit site, where discharged trnas leave the ribsme
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk INITIATION OF TRANSLATION: Initiatin brings tgether mrna, a trna with the first amin acid, and the tw ribsmal subunits First, a small ribsmal subunit binds with mrna and a special initiatr trna Then the small subunit mves alng the mrna until it reaches the start cdn (AUG) Prteins called initiatin factrs bring in the large subunit that cmpletes the translatin initiatin cmplex
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk ELONGATION OF THE POLYPEPTIDE CHAIN: During elngatin, amin acids are added ne by ne t the C-terminus f the grwing chain Each additin invlves prteins called elngatin factrs and ccurs in three steps: 1. cdn recgnitin 2. peptide bnd frmatin 3. translcatin Translatin prceeds alng the mrna in a 5 3 directin
Gene Expressin: Frm Gene t Prtein: 17.4 Translatin is the RNA-directed synthesis f a plypeptide: a clser lk TERMINATION OF TRANSLATION: Terminatin ccurs when a stp cdn in the mrna reaches the A site f the ribsme The A site accepts a prtein called a release factr The release factr causes the additin f a water mlecule instead f an amin acid This reactin releases the plypeptide, and the translatin assembly cmes apart