BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 10 Protein Synthesis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The information constituting an organism’s genotype is carried in the sequence of bases in DNA The flow of information is from DNA to RNA to protein THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A specific gene specifies a polypeptide –The DNA is transcribed into RNA, which is translated into the polypeptide Figure 10.6A DNA RNA Protein TRANSCRIPTION TRANSLATION
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Studies of inherited metabolic disorders first suggested that phenotype is expressed through proteins Studies of the bread mold Neurospora crassa led to the one gene-one polypeptide hypothesis Figure 10.6B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutate wild type fungus *Supply all mutant isolates with complete media *Grow purified mutants with minimal media to find nutritional mutants *Determine what is the nutritional limitation find mutation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings There for the gene used to produce an enzyme that helps cells manufacture Arginine amino acid was mutated in that fungal strain
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Transcription produces genetic messages in the form of RNA Figure 10.9A RNA polymerase RNA nucleotide Direction of transcription Newly made RNA Template strand of DNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA Transcription Process in which the genetic information on DNA is transferred to RNA During transcription only 1 DNA stand serves as the template or pattern from which RNA is formed.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In transcription, the DNA helix unzips –RNA nucleotides line up along one strand of the DNA following the base-pairing rules –The single-stranded messenger RNA peels away and the DNA strands rejoin RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation Elongation Termination Area shown in Figure 10.9A Growing RNA RNA polymerase Completed RNA Figure 10.9B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA Transcription 1.Initiation The enzyme RNA polymerase attaches to the promoter site on the DNA Promoter – a sequence of nucleotides that is found on one of the DNA strands –tells RNA polymerase to start transcription and which of the two DNA strands to transcribe
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA Transcription 2.Elongation RNA nucleotides attach to the free DNA nucleotides by hydrogen bonds one at a time As RNA synthesis continues the growing RNA strand peels away from the DNA and the DNA strands rejoin
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA Transcription 3.Termination RNA polymerase reaches the terminator. Terminator – a sequence of bases on DNA that signals the end of the gene The RNA polymerase detaches from the DNA and the RNA molecule is complete
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Noncoding segments called introns are spliced out The coding segments called exons are joined together A cap and a tail are added to the ends Eukaryotic RNA is processed before leaving the nucleus Figure DNA RNA transcript with cap and tail mRNA ExonIntron Exon Transcription Addition of cap and tail Introns removed Exons spliced together Coding sequence NUCLEUS CYTOPLASM Tail Cap
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The “words” of the DNA “language” are triplets of bases called codons –The codons in a gene specify the amino acid sequence of a polypeptide Genetic information written in codons is translated into amino acid sequences
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.7 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Virtually all organisms share the same genetic code The genetic code is the Rosetta stone of life Figure 10.8A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An exercise in translating the genetic code Figure 10.8B Start codon RNA Transcribed strand Stop codon Translation Transcription DNA Polypeptide
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation The process in which a polypeptide is synthesized using the genetic information encoded on an mRNA molecule The following are needed for translation to occur 1.mRNA -Contains the instructions for the assembly of proteins -Codon – a sequence of 3 bases on mRNA that specifies a specific amino acid that will be added to the polypeptide chain
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide The process is aided by transfer RNAs Transfer RNA molecules serve as interpreters during translation Figure 10.11A Hydrogen bond Amino acid attachment site RNA polynucleotide chain Anticodon
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other Figure 10.11B, C Anticodon Amino acid attachment site
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation 2.tRNA (transfer RNA) Carries an amino acid to the ribosome A tRNA molecule is composed of –A single strand of RNA (about 80 nucleotides) –A loop at one end that contains the anticodon –Anticodon – a sequence of 3 bases on tRNA that are complementary to the bases on mRNA –At the opposite end of the loop is a site where an amino acit can attach
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation 3. Amino acids Located in the cytoplasm Synthesized from other chemicals or obtained from food
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ribosomes build polypeptides Figure 10.12A-C Codons tRNA molecules mRNA Growing polypeptide Large subunit Small subunit mRNA mRNA binding site P siteA site PA Growing polypeptide tRNA Next amino acid to be added to polypeptide
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation 4.Ribosomes Organelles where protein synthesis occurs Consists of 2 subunits each made up of proteins and ribosomal RNA (rRNA) –Small subunit – has binding site for mRNA –Large subunit – has binding site for tRNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An initiation codon marks the start of an mRNA message Figure 10.13A End Start of genetic message
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Figure 10.13B 1 Initiator tRNA mRNA Start codon Small ribosomal subunit 2 P site Large ribosomal subunit A site
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure (continued) 4 Stage Elongation Growing polypeptide Codons 5 Stage Termination mRNA New peptide bond forming Stop Codon The ribosome recognizes a stop codon. The poly- peptide is terminated and released. A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. Polypeptide
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The mRNA moves a codon at a time relative to the ribosome –A tRNA pairs with each codon, adding an amino acid to the growing polypeptide Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure Codon recognition Amino acid Anticodon A site P site Polypeptide 2 Peptide bond formation 3 Translocation New peptide bond mRNA movement mRNA Stop codon
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Steps of Translation 1.Initiation mRNA binds to the ribosome The start codon (AUG) is reached The first amino acid (methionine) is brought to the ribosome by the tRNA 2.Elongation Amino acids are added one by one to a growing polypeptide chain
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Steps of Translation 3.Termination The stop codon is reached The completed polypeptide is released
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Modification of the polypeptide Endoplasmic reticulum Collects proteins made by the ribosomes Packages them into vesicles which move to the Golgi apparatus Golgi apparatus Proteins are altered, packaged into vesicles, and transported to different parts of the cell or exported out of the cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Summary of transcription and translation Figure Stage mRNA is transcribed from a DNA template. Anticodon DNA mRNA RNA polymerase TRANSLATION Enzyme Amino acid tRNA Initiator tRNA Large ribosomal subunit Small ribosomal subunit mRNA Start Codon 2 Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 3 Stage Initiation of polypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. TRANSCRIPTION
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The sequence of codons in DNA spells out the primary structure of a polypeptide –Polypeptides form proteins that cells and organisms use Review: The flow of genetic information in the cell is DNA RNA protein
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutations are changes in the DNA base sequence –These are caused by errors in DNA replication or by mutagens –The change of a single DNA nucleotide causes sickle-cell disease Mutations can change the meaning of genes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.16A Normal hemoglobin DNA mRNA Normal hemoglobin Glu Mutant hemoglobin DNA mRNA Sickle-cell hemoglobin Val
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Types of mutations Figure 10.16B mRNA NORMAL GENE BASE SUBSTITUTION BASE DELETION ProteinMetLysPheGlyAla MetLysPheSerAla MetLysLeuAlaHis Missing
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Types of Mutations There are 2 general categories of mutations: 1.Base substitution The replacement of one nucleotide with another Can result in no change in the protein An insignificant change –The altered amino acid has no effect on the function of the protein
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Types of Mutations A change that is crucial to life of the organism –The altered amino acid has an effect on the function of the protein 2.Base insertions or deletions One or more bases are added or deleted from the DNA Often have disastrous effects –The nucleotide sequence following the change alters the genetic message (reading frame)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutations are Useful Mutations are useful because they 1.Provide diversity that allows evolution by natural selection to occur 2.Essential tool for geneticists Create different alleles needed for genetic research