* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download video slide - Your School
DNA supercoil wikipedia , lookup
RNA interference wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Metalloprotein wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Real-time polymerase chain reaction wikipedia , lookup
Proteolysis wikipedia , lookup
Non-coding DNA wikipedia , lookup
RNA silencing wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Biochemistry wikipedia , lookup
Polyadenylation wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
RNA polymerase II holoenzyme wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Point mutation wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Transcriptional regulation wikipedia , lookup
Gene expression wikipedia , lookup
Transfer RNA wikipedia , lookup
Genetic code wikipedia , lookup
Messenger RNA wikipedia , lookup
From Gene to Protein PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DNA RNA Protein synthesis • The DNA inherited by an organism – Leads to specific traits by dictating the synthesis of proteins • The process by which DNA directs protein synthesis, gene expression – Includes two stages, called transcription and translation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The ribosome – Is part of the cellular machinery for translation Figure 17.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 17.1: Genes specify proteins via transcription and translation DNA Replication- Making a copy of DNA from a DNA template strand. Transcription- Making an RNA molecule from a DNA template strand. Translation- Making a protein from a mRNA template strand. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Basic Principles of Transcription and Translation • Transcription – Is the synthesis of RNA under the direction of DNA – Produces messenger RNA (mRNA) • Translation – Is the actual synthesis of a polypeptide, which occurs under the direction of mRNA – Occurs on ribosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In prokaryotes – Transcription and translation occur together DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide (a) Prokaryotic cell. In a cell lacking a nucleus, mRNA produced by transcription is immediately translated without additional processing. Figure 17.3a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In eukaryotes – RNA transcripts are modified before becoming true mRNA Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA Ribosome TRANSLATION Polypeptide Figure 17.3b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Eukaryotic cell. The nucleus provides a separate compartment for transcription. The original RNA transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA. Cells are governed by a cellular chain of command – DNA RNA protein Processes: Transcription Translation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Genetic Code • How many bases correspond to an amino acid? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Codons: Triplets of Bases • Genetic information – Is encoded as a sequence of nonoverlapping base triplets, or codons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings During transcription – The gene determines the sequence of bases along the length of an mRNA molecule Gene 2 DNA molecule Gene 1 Gene 3 DNA strand (template) 3 A C C A A A C C U G G U U U G G A G T 5 TRANSCRIPTION mRNA 5 G C U C 3 Codon TRANSLATION Protein Figure 17.4 Trp Amino acid Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Phe Gly Ser Cracking the Code • A codon in messenger RNA Figure 17.5 Second mRNA base U C A UAU UUU UCU Tyr Phe UAC UUC UCC U UUA UCA Ser UAA Stop UAG Stop UUG Leu UCG CUU CUC C CUA CUG CCU CCC Leu CCA CCG Pro AUU AUC A AUA AUG ACU ACC ACA ACG Thr GUU G GUC GUA GUG lle Met or start GCU GCC Val GCA GCG Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ala G U UGU Cys UGC C UGA Stop A UGG Trp G U CAU CGU His CAC CGC C Arg CAA CGA A Gln CAG CGG G U AAU AGU Asn AAC AGC Ser C A AAA AGA Lys Arg G AAG AGG U GAU GGU C GAC Asp GGC Gly GAA GGA A Glu GAG GGG G Third mRNA base (3 end) First mRNA base (5 end) – Is either translated into an amino acid or serves as a translational stop signal Codons must be read in the correct reading frame – For the specified polypeptide to be produced Consider this sentence: “The red dog ate the cat” Grouping in the wrong order reads as: “her edd oga tet hec at.” **The reading frame is important as a genetic message that tells the cell’s protein synthesizing machinery the EXACT message. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of the Genetic Code • The genetic code is nearly universal – Shared by organisms from the simplest bacteria to the most complex animals Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In laboratory experiments – Genes can be transcribed and translated after being transplanted from one species to another. – The RNA codon CCG, for instance, translates to the amino acid proline in all organisms whose genetic code has been examined. Figure 17.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Check it! • http://www.technologyreview.com/view/413616/ glowing-monkeys-inherit-jellyfish-genes/ Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A baby marmoset! Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Another baby marmoset! Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The ribosomes – Are constructed of proteins and RNA molecules named ribosomal RNA or rRNA DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide Exit tunnel Growing polypeptide tRNA molecules Large subunit E P A Small subunit 5 mRNA Figure 17.16a 3 (a) Computer model of functioning ribosome. This is a model of a bacterial ribosome, showing its overall shape. The eukaryotic ribosome is roughly similar. A ribosomal subunit is an aggregate of ribosomal RNA molecules and proteins. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Building a Polypeptide • We can divide translation into three stages – Initiation – Elongation – Termination Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ribosome Association and Initiation of Translation • The initiation stage of translation – Brings together mRNA, tRNA bearing the first amino acid of the polypeptide, and two subunits of a ribosome P site 3 U A C 5 5 A U G 3 Initiator tRNA Large ribosomal subunit GTP GDP E A mRNA 5 Start codon mRNA binding site Figure 17.17 3 Small ribosomal subunit 1 A small ribosomal subunit binds to a molecule of mRNA. In a prokaryotic cell, the mRNA binding site on this subunit recognizes a specific nucleotide sequence on the mRNA just upstream of the start codon. An initiator tRNA, with the anticodon UAC, base-pairs with the start codon, AUG. This tRNA carries the amino acid methionine (Met). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5 3 Translation initiation complex 2 The arrival of a large ribosomal subunit completes the initiation complex. Proteins called initiation factors (not shown) are required to bring all the translation components together. GTP provides the energy for the assembly. The initiator tRNA is in the P site; the A site is available to the tRNA bearing the next amino acid. Elongation of the Polypeptide Chain • In the elongation stage of translation – Amino acids are added one by one to the preceding amino acid TRANSCRIPTION Amino end of polypeptide DNA mRNA Ribosome TRANSLATION Polypeptide mRNA Ribosome ready for next aminoacyl tRNA E 3 P A site site 5 1 Codon recognition. The anticodon of an incoming aminoacyl tRNA base-pairs with the complementary mRNA codon in the A site. Hydrolysis of GTP increases the accuracy and efficiency of this step. 2 GTP 2 GDP E E P P A GDP Figure 17.18 3 Translocation. The ribosome translocates the tRNA in the A site to the P site. The empty tRNA in the P site is moved to the E site, where it is released. The mRNA moves along with its bound tRNAs, bringing the next codon to be translated into the A site. GTP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings E P A A 2 Peptide bond formation. An rRNA molecule of the large subunit catalyzes the formation of a peptide bond between the new amino acid in the A site and the carboxyl end of the growing polypeptide in the P site. This step attaches the polypeptide to the tRNA in the A site. Termination of Translation • The final stage of translation is termination – When the ribosome reaches a stop codon in the mRNA Release factor Free polypeptide 5 3 3 5 5 3 Stop codon (UAG, UAA, or UGA) 1 When a ribosome reaches a stop 2 The release factor hydrolyzes 3 The two ribosomal subunits codon on mRNA, the A site of the the bond between the tRNA in and the other components of ribosome accepts a protein called the P site and the last amino the assembly dissociate. a release factor instead of tRNA. acid of the polypeptide chain. The polypeptide is thus freed from the ribosome. Figure 17.19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 17.5: RNA plays multiple roles in the cell: a review • RNA – Can hydrogen-bond to other nucleic acid molecules – Can assume a specific three-dimensional shape – Has functional groups that allow it to act as a catalyst Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of RNA in a Eukaryotic Cell Know these 3! Table 17.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The change of a single nucleotide in the DNA’s template strand – Leads to the production of an abnormal protein Wild-type hemoglobin DNA 3 Mutant hemoglobin DNA 5 C T T In the DNA, the mutant template strand has an A where the wild-type template has a T. G U A The mutant mRNA has a U instead of an A in one codon. 3 5 T C A mRNA mRNA G A A 5 3 5 3 Normal hemoglobin Sickle-cell hemoglobin Glu Val Figure 17.23 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The mutant (sickle-cell) hemoglobin has a valine (Val) instead of a glutamic acid (Glu). Mutagens • Spontaneous mutations – Can occur during DNA replication, recombination, or repair Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mutagens – Are physical or chemical agents that can cause mutations – Examples: Environmental factors (toxins), Cigarette smoke, radioactive element, UV radiation (from sunlight) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What is a gene? revisiting the question • A gene – Is a region of DNA whose final product is either a polypeptide or an RNA molecule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A summary of transcription and translation in a eukaryotic cell DNA TRANSCRIPTION 1 RNA is transcribed from a DNA template. 3 RNA transcript 5 RNA polymerase RNA PROCESSING Exon 2 In eukaryotes, the RNA transcript (premRNA) is spliced and modified to produce mRNA, which moves from the nucleus to the cytoplasm. RNA transcript (pre-mRNA) Intron Aminoacyl-tRNA synthetase NUCLEUS Amino acid tRNA FORMATION OF INITIATION COMPLEX CYTOPLASM 3 After leaving the nucleus, mRNA attaches to the ribosome. AMINO ACID ACTIVATION 4 Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. mRNA Growing polypeptide Activated amino acid Ribosomal subunits 5 TRANSLATION 5 E A AAA UG GUU UA U G Codon Figure 17.26 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ribosome A succession of tRNAs add their amino acids to Anticodon the polypeptide chain as the mRNA is moved through the ribosome one codon at a time. (When completed, the polypeptide is released from the ribosome.)