From DNA to Protein

1. From DNA to Protein Chapter 14

3. Ricin and your Ribosomes

5. DNA and RNA RNAs have various functions. Some serve as disposable copies of DNA’s genetic message; others are catalytic. DNA has one function: It permanently stores a cell’s genetic information, which is passed to offspring.

6. DNA template Transcription mRNA Translation Gly stop protein Glu Amino acid Amino acid Amino acid

7. Converting a Gene to an RNA • Transcription • Enzymes use the nucleotide sequence of a gene to synthesize a complementary strand of RNA • Occurs in the nucleus

8. Converting mRNA to Protein • Translation • The information carried by mRNA is decoded into a sequence of amino acids, resulting in a polypeptide chain

9. RNA in Protein Synthesis3 Different Kinds of RNA: • Messenger RNA (mRNA) Contains information transcribed from DNA • Ribosomal RNA (rRNA) Main component of ribosomes, where polypeptide chains are built • Transfer RNA (tRNA) Delivers amino acids to ribosomes

10. Gene Expression • Gene expression A multistep process in which genetic information encoded by a gene is converted into a structural or functional part of a cell or body

11. Transcription: DNA to RNA • RNA polymerase assembles RNA by linking RNA nucleotides into a chain • A new RNA strand is complementary in sequence to the DNA strand from which it was transcribed

12. Transcription: DNA to RNA DNA template Transcription mRNA

13. Base-Pairing in DNA Synthesis and Transcription

14. The Process of Transcription • RNA polymerase and regulatory proteins attach to a promoter (a specific binding site in DNA close to the start of a gene) • RNA polymerase moves over the gene in a 5' to 3' direction, unwinds the DNA helix, reads the base sequence, and joins free RNA nucleotides into a complementary strand of mRNA

15. (gene)

17. Fig. 14-5a, p. 218

18. Post-Transcriptional Modifications exon intron exon intron exon gene DNA transcription into RNA poly-A tail cap Pre- 3’ mRNA 5’ snipped out snipped out mRNA Fig. 14-7, p. 220

19. mRNA – The Messenger • Codon-A sequence of three mRNA nucleotides that codes for a specific amino acid • The order of codons in mRNA determines the order of amino acids in a polypeptide chain

20. Genetic Information • From DNA to mRNA to amino acid sequence codon

21. Codons of the Genetic Code

22. rRNA and tRNA – The Translators • tRNAs deliver amino acids to ribosomes • tRNA has an anticodon

23. Ribosomes 2 subunits Ribosomes made of rRNA & proteins

24. Translation: RNA to Protein • Translation converts genetic information carried by an mRNA into a new polypeptide chain

25. Translation • Translation occurs in the cytoplasm of cells • Translation occurs in three stages • Initiation • Elongation • Termination

27. Elongation

28. Elongation C An initiator tRNA carries the amino acid methionine, so the first amino acid of the new polypeptide chain will be methionine. A second tRNA binds the second codon of the mRNA (here, that codon is GUG, so the tRNA that binds carries the amino acid valine). A peptide bond forms between the first two amino acids (here, methionine and valine). Fig. 14-12c, p. 223

29. D The first tRNA is released and the ribosome moves to the next codon in the mRNA. A third tRNA binds to the third codon of the mRNA (here, that codon is UUA, so the tRNA carries the amino acid leucine). A peptide bond forms between the second and third amino acids (here, valine and leucine). Fig. 14-12d, p. 223

30. E The second tRNA is released and the ribosome moves to the next codon. A fourth tRNA binds the fourth mRNA codon (here, that codon is GGG, so the tRNA carries the amino acid glycine). A peptide bond forms between the third and fourth amino acids (here, leucine and glycine). Fig. 14-12e, p. 223

31. Termination • When the ribosome encounters a stop codon, polypeptide synthesis ends • Release factors bind to the ribosome • Enzymes detach the mRNA and polypeptide chain from the ribosome

32. Mutated Genes & Their Protein Products • If the nucleotide sequence of a gene changes, it may result in an altered gene product, with harmful effects • Mutations • Small-scale changes in the nucleotide sequence of a cell’s DNA that alter the genetic code

33. Common Mutations • Base-pair-substitution • Deletion or insertion

34. Normal • Hemoglobin chain THREONINE PROLINE GLUTAMATE GLUTAMATE LYSINE b. Base pair substitution THREONINE PROLINE VALINE GLUTAMATE LYSINE c. Frame shift THREONINE PROLINE GLYCINE ARGININE Fig. 14-13, p. 224

35. What Causes Mutations? • Spontaneous mutations • Uncorrected errors in DNA replication • Harmful environmental agents 2. UV radiation 3. chemicals

36. Mutations Caused by Radiation • Ionizing radiation damages chromosomes, nonionizing (UV) radiation forms thymine dimers

37. Inherited Mutations • Mutations in somatic cells of sexually reproducing species are not inherited • Mutations in a germ cell or gamete may be inherited, with evolutionary consequences

39. Assembly of RNA on unwound regions of DNA molecule Transcription mRNA rRNA tRNA mRNA processing proteins mature tRNA mature mRNA transcripts ribosomal subunits Convergence of RNAs Translation cytoplasmic pools of amino acids, ribosomal subunits, and tRNAs At an intact ribosome, synthesis of a polypeptide chain at the binding sites for mRNA and tRNAs Protein Fig. 14-16, p. 226