1. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 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 The information constituting an organism’s genotype –Is carried in its sequence of its DNA bases A particular gene, a linear sequence of many nucleotides –Specifies a polypeptide

2. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The DNA of the gene is transcribed into RNA –Which is translated into the polypeptide Figure 10.6A DNA Transcription RNA Protein Translation

3. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Genetic information written in codons is translated into amino acid sequences 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

4. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings DNA strand Transcription Translation Polypeptide RNA Amino acid Codon A AA C C GG C A AA A U UU G G CC G U UU U Gene 1 Gene 2 Gene 3 DNA molecule Figure 10.7

5. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The genetic code is the Rosetta stone of life Nearly all organisms –Use exactly the same genetic code UUG

6. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings RNA codon table, with corresponding amino acids

7. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings An exercise in translating the genetic code Figure 10.8B TA CTTCAAAATC AT GAAGTTTTAG AU G AAGU UUUAG Transcription Translation RNA DNA Met LysPhePolypeptide Start condon Stop condon Strand to be transcribed

8. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transcription produces genetic messages in the form of RNA A close-up view of transcription RNA polymerase RNA nucleotides Direction of transcription Template Strand of DNA Newly made RNA T C A T CC A A T T G G C C A A TT GGAT G U C AUCCA A U Figure 10.9A

9. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings In the nucleus, the DNA helix unzips –And RNA nucleotides line up along one strand of the DNA, following the base pairing rules As the single-stranded messenger RNA (mRNA) peels away from the gene –The DNA strands rejoin

10. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transcription of a gene RNA polymerase DNA of gene Promoter DNA Terminator DNA Area shown In Figure 10.9A Growing RNA Completed RNA RNA polymerase Figure 10.9B 1 Initiation 2 Elongation 3 Termination

11. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Eukaryotic RNA is processed before leaving the nucleus Noncoding segments called introns are spliced out –And a cap and a tail are added to the ends Exon Intron Exon Intron Exon DNA Cap Transcription Addition of cap and tail RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm Figure 10.10

12. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transfer RNA molecules serve as interpreters during translation Translation –Takes place in the cytoplasm

13. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings A ribosome attaches to the mRNA –And translates its message into a specific polypeptide aided by transfer RNAs (tRNAs) Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon Figure 10.11A

14. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Each tRNA molecule –Is a folded molecule bearing a base triplet called an anticodon on one end A specific amino acid –Is attached to the other end Amino acid attachment site Anticodon Figure 10.11B, C

15. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Ribosomes build polypeptides A ribosome consists of two subunits –Each made up of proteins and a kind of RNA called ribosomal RNA tRNA molecules mRNA Small subunit Growing polypeptide Large subunit Figure 10.12A

16. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The subunits of a ribosome –Hold the tRNA and mRNA close together during translation Large subunit mRNA- binding site Small subunit tRNA-binding sites Growing polypeptide Next amino acid to be added to polypeptide mRNA tRNA Codons Figure 10.12B, C

17. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings An initiation codon marks the start of an mRNA message Start of genetic message End Figure 10.13A

18. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings mRNA, a specific tRNA, and the ribosome subunits –Assemble during initiation Met Initiator tRNA 1 2 mRNA Small ribosomal subunit Start codon Large ribosomal subunit A site U A CA U C A U G P site Figure 10.13B

19. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 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

20. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Each addition of an amino acid –Occurs in a three-step elongation process Polypeptide P site mRNA Codons mRNA movement Stop codon New Peptide bond Anticodon Amino acid A site Figure 10.14 1 Codon recognition 2 Peptide bond formation 3 Translocation

21. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The mRNA moves a codon at a time –And a tRNA with a complementary anticodon pairs with each codon, adding its amino acid to the peptide chain

22. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Elongation continues –Until a stop codon reaches the ribosome’s A site, terminating translation

23. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Review: The flow of genetic information in the cell is DNA  RNA  protein The sequence of codons in DNA, via the sequence of codons –Spells out the primary structure of a polypeptide

24. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Polypeptide Transcription DNA mRNA RNA polymerase Amino acidTranslation tRNA Enzyme Anticodon ATP Initiator tRNA Large ribosomal subunit Start Codon Codons mRNA Stop codon Small ribosomal subunit Growing polypeptide New peptide bond forming mRNA Figure 10.15 Summary of transcription and translation mRNA is transcribed from a DNA template. 1 Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 2 Initiation of polypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. 3 Elongation 4 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. 5 The ribosome recognizes a stop codon. The poly-peptide is terminated and released. Termination

25. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Mutations can change the meaning of genes Mutations are changes in the DNA base sequence –Caused by errors in DNA replication or recombination, or by mutagens C TTC AT Normal hemoglobin Mutant hemoglobin DNA GAAGUA Sickle-cell hemoglobin Normal hemoglobin DNA Glu Val mRNA Figure 10.16A

26. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Substituting, inserting, or deleting nucleotides alters a gene –With varying effects on the organism Normal gene mRNA Base substitution Base deletion Missing MetLys Phe Gly Ala Met Lys PheSerAla Met Lys Leu AlaHis AUGA A G U U U G G C GC A AUGA A G U U U A G C GC A AUGA A G U U GGCG CA U U Protein Figure 10.16B