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Chapter 10 Molecular Biology of the Gene PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE • TAYLOR • SIMON • DICKEY • HOGAN © 2015 Pearson Education, Inc. Lecture by Edward J. Zalisko • DNA • DNA Replication • DNA Transcription and Translation © 2015 Pearson Education, Inc. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN © 2015 Pearson Education, Inc. • Intro to Transcription and Translation © 2015 Pearson Education, Inc. 10.6 Genes control phenotypic traits through the expression of proteins • DNA specifies traits by dictating synthesis. • Proteins are the links between genotype and phenotype. • The molecular chain of command is from DNA in the nucleus to RNA and RNA in the cytoplasm to protein. © 2015 Pearson Education, Inc. 10.6 Genes control phenotypic traits through the expression of proteins • is the synthesis of RNA under the direction of DNA. • is the synthesis of proteins under the direction of RNA. © 2015 Pearson Education, Inc. Figure 10.6a-3 DNA Transcription RNA NUCLEUS Translation Protein © 2015 Pearson Education, Inc. CYTOPLASM 10.6 Genes control phenotypic traits through the expression of proteins • Genes provide the instructions for making specific proteins. • The sequence of nucleotides in DNA provides a code for constructing a protein. • Protein construction requires a conversion of a nucleotide sequence to an amino acid sequence. • Transcription rewrites the DNA code into RNA using the same nucleotide “language.” © 2015 Pearson Education, Inc. Answer in Notebooks #6. Describe the significance of Transcription and Translation. © 2015 Pearson Education, Inc. 10.9 VISUALIZING THE CONCEPT: Transcription produces genetic messages in the form of RNA • Transcription of a gene occurs in three main steps: 1. , involving the attachment of RNA polymerase to the promoter and the start of RNA synthesis 2. , as the newly formed RNA strand grows 3. , when RNA polymerase reaches the terminator DNA and the polymerase molecule detaches from the newly made RNA strand and the gene. © 2015 Pearson Education, Inc. Animation: Transcription © 2015 Pearson Education, Inc. Figure 10.9-3 Direction of transcription Initiation RNA synthesis begins after RNA polymerase attaches to the promoter. Unused strand of DNA RNA polymerase Terminator DNA DNA of gene Newly formed RNA Promoter Elongation Template strand of DNA Direction of transcription Using the DNA as a template, RNA polymerase adds free RNA nucleotides one at a time. Free RNA nucleotide DNA strands reunite T C C A A U C C A A GG T T DNA strands separate Newly made RNA Termination RNA synthesis ends when RNA polymerase reaches the terminator DNA sequence. Terminator DNA Completed RNA RNA polymerase detaches © 2015 Pearson Education, Inc. 10.10 Eukaryotic RNA is processed before leaving the nucleus as mRNA • • encodes amino acid sequences • conveys genetic messages from DNA to the translation machinery of the cell. • Eukaryotic mRNA has sequences that separate © 2015 Pearson Education, Inc. , interrupting , the coding regions. 10.10 Eukaryotic RNA is processed before leaving the nucleus as mRNA • Eukaryotic mRNA undergoes processing before leaving the nucleus. • removes introns (intervening sequences) and joins exons (expressed sequences) to produce a continuous coding sequence. © 2015 Pearson Education, Inc. 10.10 Eukaryotic RNA is processed before leaving the nucleus as mRNA •A of extra nucleotides are added to the ends of the mRNA • facilitate the export of the mRNA from the nucleus • protect the mRNA from degradation by cellular enzymes • help ribosomes bind to the mRNA • The cap and tail themselves are not translated into protein. © 2015 Pearson Education, Inc. Figure 10.10 Exon DNA Exon Intron Cap RNA transcript with cap and tail Exon Intron Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM © 2015 Pearson Education, Inc. 10.7 Genetic information written in codons is translated into amino acid sequences • The flow of information from gene to protein is based on a triplet code. • The genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of nonoverlapping three-base “words” called . • Transcribe the following DNA codons into mRNA codons. TAC © 2015 Pearson Education, Inc. CGA ACA ATC Answer in Notebooks: #7. Find the DNA codons for the mRNA codons below: AUG © 2015 Pearson Education, Inc. CUC UUA CGC 10.11 Transfer RNA molecules serve as interpreters during translation • molecules function as an interpreter, converting the genetic message of mRNA into the language of proteins. • Transfer RNA molecules perform this interpreter task by • picking up the appropriate amino acid • using a special triplet of bases, called an , to recognize the appropriate codons in the mRNA. © 2015 Pearson Education, Inc. Figure 10.11a Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon A tRNA molecule, showing its polynucleotide strand and hydrogen bonding © 2015 Pearson Education, Inc. A simplified representation of a tRNA Find the tRNA anticodons for the mRNA codons below: AUG © 2015 Pearson Education, Inc. CUC UUA CGC Answer in Notebooks: #8. Given the tRNA anticodons write the corresponding mRNA codons. UAC © 2015 Pearson Education, Inc. AUU GCA UCG Answer in Notebooks: #9. Translate and transcribe the following DNA into mRNA and tRNA. TAC © 2015 Pearson Education, Inc. ATT GCA ACT Answer in Notebooks: #10. Translate and transcribe the following mRNA into DNA and tRNA. AUG © 2015 Pearson Education, Inc. GCA GCG GUA 10.12 Ribosomes build polypeptides • Translation occurs on the surface of the ribosome. • Ribosomes coordinate the functioning of mRNA and tRNA and, ultimately, the synthesis of polypeptides. • Ribosomes have two subunits: small and large. • Each subunit is composed of ribosomal RNAs and proteins. • Ribosomal subunits come together during translation. • Ribosomes have binding sites for mRNA and tRNAs. © 2015 Pearson Education, Inc. Figure 10.12-0 tRNA molecules tRNA binding sites Growing polypeptide Ribosome Large subunit P A site site Small subunit mRNA binding site The next amino acid to be added to the polypeptide Growing polypeptide mRNA tRNA Codons © 2015 Pearson Education, Inc. 10.13 An initiation codon marks the start of an mRNA message • Translation can be divided into the same three phases as transcription: 1. initiation 2. elongation 3. Termination • Initiation brings together • mRNA, • a tRNA bearing the first amino acid • the two subunits of a ribosome Pearson Education, Inc. Education, ©© 2015 2015 Pearson 10.13 An initiation codon marks the start of an mRNA message • Initiation establishes where translation will begin. • Initiation occurs in two steps. 1. An mRNA molecule binds to a small ribosomal subunit, and a special initiator tRNA binds to mRNA at the codon. Pearson Education, Inc. Education, ©© 2015 2015 Pearson 10.13 An initiation codon marks the start of an mRNA message 2. A large ribosomal subunit joins the small subunit, allowing the ribosome to function. • The first tRNA occupies the hold the growing polypeptide. , which will • The is available to receive the next amino-acid-bearing tRNA. Pearson Education, Inc. Education, ©© 2015 2015 Pearson Figure 10.13a Start of genetic message Cap End Tail © 2015 Pearson Education, Inc. Figure 10.13b-2 Large ribosomal subunit Initiator tRNA mRNA P site A site U A C U A C A U G A U G Start codon 1 © 2015 Pearson Education, Inc. Small ribosomal subunit 2 10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation • Once initiation is complete, amino acids are added one by one to the first amino acid. • Each addition occurs in a three-step elongation process. © 2015 Pearson Education, Inc. Figure 10.14-4 Amino acid Anticodon A site Polypeptide P site mRNA Codons 1 Codon recognition mRNA movement Stop codon New peptide bond 3 Translocation © 2015 Pearson Education, Inc. 2 Peptide bond formation 10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation • Elongation continues until the termination stage of translation, when • the ribosome reaches a codon • the completed polypeptide is freed from the last tRNA • the ribosome splits back into its separate subunits. © 2015 Pearson Education, Inc. Animation: Translation © 2015 Pearson Education, Inc. 10.8 The genetic code dictates how codons are translated into amino acids • The is the amino acid translations of each of the nucleotide triplets. • Three nucleotides specify one amino acid. • Sixty-one codons correspond to amino acids. • AUG codes for methionine and signals the start of transcription. • Three “stop” codons signal the end of translation. © 2015 Pearson Education, Inc. 10.8 The genetic code dictates how codons are translated into amino acids • The genetic code is • , with more than one codon for some amino acids • , in that any codon for one amino acid does not code for any other amino acid • , in that the genetic code is shared by organisms from the simplest bacteria to the most complex plants and animals. © 2015 Pearson Education, Inc. Figure 10.8a Second base of RNA codon C A UUU U UUC First base of RNA codon UUA C A Leu UCU UAU UCC UAC UCA Ser Tyr UGU UGC Cys U C UAA Stop UGA Stop A UUG UCG UAG Stop UGG Trp G CUU CCU CAU U CUC CCC CAC Leu Pro CAA His CGU CGC CGA CUA CCA CUG CCG CAG CGG AUU ACU AAU AGU ACC AAC AUC lle AUA G ACA Thr Asn AAA AGA GUU GAU GUC GUG GCC Val GCA GCG GAC Ala GAA GAG Ser Glu GGC GGA GGG A U C Arg A G GGU Asp C G AGC AAG Lys AGG GCU Arg Gln or AUG Met ACG start GUA © 2015 Pearson Education, Inc. Phe G U Gly C A G Third base of RNA codon U © 2015 Pearson Education, Inc. Figure 10.8b-3 Strand to be transcribed T A C T T C A A A A T C G A A G T T T T A G A U G A A G U U U U A G DNA A T Transcription RNA Translation Start codon Polypeptide Met © 2015 Pearson Education, Inc. Stop codon Lys Phe Answer in Notebooks: #11. Transcribe the following mRNA to proteins. UAC © 2015 Pearson Education, Inc. AUU GCA UCG Answer in Notebooks: #12. Translate and Transcribe the following DNA to mRNA to proteins – include tRNA anticodons. DNA: mRNA: tRNA: Proteins: © 2015 Pearson Education, Inc. TAC GGA TCT ATC Answer in Notebooks: Translate and Transcribe #13 the Following: (DNA – mRNA – Anticodon (tRNA) – Amino Acid) T A C AUG UAC Met ATG UAC AUG Tyr CGC GCG CGC ala TCC AGG UCC arg GCC CGG GCC arg GTC CAG GUC Glu ATG UAC AUG tyr AAT UUA AAU leu ACC UGG ACC try ACT UGA ACU stop © 2015 Pearson Education, Inc. 10.15 Review: The flow of genetic information in the cell is DNA RNA protein • The flow of genetic information is from DNA to RNA to protein. • In transcription (DNA → RNA), the mRNA is synthesized on a DNA template. • In eukaryotic cells, transcription occurs in the nucleus, and the messenger RNA is processed before it travels to the cytoplasm. • In prokaryotes, transcription occurs in the cytoplasm. © 2015 Pearson Education, Inc. Figure 10.15-5 DNA Transcription mRNA NUCLEUS Transcription 1 RNA polymerase CYTOPLASM Translation Amino acid Amino acid attachment Enzyme 2 tRNA Initiator tRNA UA C AU G mRNA Start codon ATP Large ribosomal subunit Anticodon 3 Initiation of polypeptide synthesis Small ribosomal subunit New peptide bond forming Growing polypeptide 4 Elongation Codons mRNA Polypeptide 5 Stop codon © 2015 Pearson Education, Inc. Termination