Molecular Biology of the Gene

Transcription

1 Molecular Biology of the ene utline: Molecular Biology of the ene Readings: hapters in ampbell et al istorical enetic Material Experiments hemical Nature of Nucleic cids Structure of DN DN Replication ene Expression RN and rotein Synthesis ene echnology riffith s Bacterial ransformation Experiments Figure 10.1 Bacteriophage (hage) Structure ead ail DN ail fiber 300,000 opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 1

2 hage/?bacterial virus reproductive cycle ershey & hase (1952) Figure 10.1 ershey & hase hage Reproduction Experiments DN is the enetic material Virus attaches to bacterial cell. Virus injects DN. Virus DN directs cell to 1. make more phage DN 2. make protein parts. New phages assemble. ell lyses releasing new phages. opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 1. Nucleotides 2. Nitrogen Bases DN Structure 3. Key Investigations 1. X-Ray rystallography 2. hargaff s Rule 3. Double elix of Watson & rick hosphate group Nitrogenous base (,,, or ) hymine () Sugar (deoxyribose) 2

3 Figure 10.2B Four Nitrogenous bases are in DN DN = Nucleotide olymer Sugar-hosphate Linkage 4 N N N 3 N N N N N N N N N N N N hymine () ytosine () denine () uanine () yrimidines urines Sugar hosphate Sugar 2 Base Base 2 Nucleotide Nucleotide opyright 2005 earson Education, Inc. ublishing as Benjamin ummings hargaff s Rule Fig. 14.9ab X-Ray rystallography: Rosalind Franklin Base air Ratio : : DN was helical DN had repetitive elements 0.34 nm, 3.4 nm, 2.0nm 3

4 Watson & rick DN Model Base-airing hargaff s Rule was applied aired Nitrogen Bases DN Structure Franklin s rystallography made sense! Major groove 2 nm 3.4 nm 0.34 nm Base pair hree representations of DN ydrogen bond Ribbon model hemical structure omputer model opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 4

5 DN Replication Semiconservative DN replication DN replication is semiconservative 1. Unwinding 2. airing 3. Joining he two DN strands separate Each strand is used as a pattern to produce a complementary strand, using specific base pairing Each new DN helix has one old strand with one new strand arental molecule of DN Nucleotides Both parental strands serve as templates wo identical daughter molecules of DN nimation: DN Replication verview opyright 2009 earson Education, Inc. opyright 2005 earson Education, Inc. ublishing as Benjamin ummings Figure 10.5B DN replication loser Look DN strands have an opposite orientation end end end end Figure 10.5 DN replication loser Look New DN strands are synthesized continuously & discontinuously arental DN DN polymerase molecule DN ligase Daughter strand synthesized continuously Daughter strand synthesized in pieces opyright 2005 earson Education, Inc. ublishing as Benjamin ummings opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 5

6 E FLW F ENEI INFRMIN FRM DN RN REIN E FLW F ENEI INFRMIN FRM DN RN REIN gene is a sequence of DN that directs the synthesis of a specific protein ranscription DN is transcribed into RN ranslation RN is translated into protein he presence and action of proteins determine the phenotype of an organism opyright 2009 earson Education, Inc. opyright 2009 earson Education, Inc. opyright he Mcraw-ill ompanies, Inc. ermission required for reproduction or display. enes Specify Sequences of mino cids Normal emoglobin β chain (Sanger 1953) Valine istidine Leucine hreonine roline lutamic lutamic acid acid ene ranscription RN polymerase binds to promoter DN 1 1. Initiation DN of gene Valine istidine Leucine hreonine roline Sickle cell anemia emoglobin β chain (Ingram 1956) Valine lutamic acid 2 2. Elongation rowing RN ENE = Unit of eredity ENE = Sequence of nucleotides that determines the amino acid sequence of a protein 3 3. ermination ompleted RN opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 6

7 ene ranscription Enzyme - RN polymerase U Direction of transcription Newly made RN U RN Nucleotides U emplate Strand of DN Steps in ene ranscription Initiation: RN polymerase binds to a promoter, where the helix unwinds and transcription starts Elongation: RN nucleotides are added to the chain ermination: RN polymerase reaches a terminator sequence and detaches from the template nimation: ranscription opyright 2005 earson Education, Inc. ublishing as Benjamin ummings opyright 2009 earson Education, Inc. DN strand ranscription enetic ode Second base enetic ode 1. riplet odons & no spaces RN ranslation odon First base hird base 2. Redundant 3. Unambiguous but floppy 4. Universal olypeptide mino acid 7

8 Figure 10.8B n exercise in translating the genetic code Strand to be transcribed ypes of RN 1. Messenger RN mrn DN ranscription 2. Ribosomal RN rrn Forms ribosomes RN U U U U U Start codon ranslation Stop codon 3. ransfer RN trn olypeptide Met Lys he opyright 2005 earson Education, Inc. ublishing as Benjamin ummings Structure of trn ene Expression he entral Dogma RN leaves the nucleus and enters the cytoplasm mino acid attachment site DN ranscription Nucleus RN polynucleotide chain RN ranslation ytoplasm nticodon rotein opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 8

9 Ribosome Structure rotein Synthesis trn-binding sites 1. Initiation mrnbinding site Large Small Initiator trn mrn Met Start codon Small site Met Large site opyright 2005 earson Education, Inc. ublishing as Benjamin ummings Large rowing polypeptide mino acid trn rowing polypeptide mrn odons rotein Synthesis New peptide bond forming 3 Elongation succession of trns add their amino acids to the polypeptide chain as the mrn is moved through the ribosome, one codon at a time. mrn nticodon olypeptide odons Small Stop codon ermination 4 he ribosome recognizes a stop codon. he polypeptide is terminated and released. 9

10 10.15 Review: he flow of genetic information in the cell is DN RN protein rotein Synthesis nimation Does translation represent: DN RN or RN protein? Where does the information for producing a protein originate: DN or RN? Which one has a linear sequence of codons: rrn, mrn, or trn? Which one directly influences the phenotype: DN, RN, or protein? opyright 2009 earson Education, Inc. ene Expression in rokaryotes ranscription ranslation opyright he Mcraw-ill ompanies, Inc. ermission required for reproduction or display. mrn rotein ene Expression in Eukaryotes DN Intron ranscription rimary RN transcript rocessing 5 mrn 3 ap ail ranslation rotein Figure Eukaryotic mrn is processed before leaving the nucleus RN transcript with cap and tail DN Exon Intron Exon Intron Exon ap Introns removed ranscription ddition of cap and tail Exons spliced together mrn oding sequence Nucleus mrn ail ytoplasm opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 10

11 Eukaryotic RN may be spliced in more than one way lternative splicing may generate two or more types of mrn from the same transcript DN Exons END RN transcript mrn or ene Expression opyright 2005 earson Education, Inc. ublishing as Benjamin ummings 11