Chapter 10.1

1. Chapter 10.1 From Genes to Proteins Grade 10 Biology Spring 2011

2. Bell Ringer • Complete this table as we take a journey learning about RNA:

3. Objectives • Compare the structure of RNA with that of DNA • Summarize the process of transcription • Relate the role of codons to the sequence of amino acids that results after translation • Outline the major steps of translation • Discuss the evolutionary significance of the genetic code

4. Section 1: part 1 http://www.youtube.com/watch?v=983lhh20rGY

5. Decoding the Information in DNA • Traits are determined by proteins that are built according to instructions coded in DNA • Ex. Eye colour • Proteins are not built directly from DNA • Ribonucleic acid is involved (RNA)

6. Decoding the Information in DNA • RNA: nucleic acid, molecule made of nucleotides linked together

7. Decoding the Information in DNA • RNA differs from DNA in 3 ways: • Single strand of nucleotides • Contain 5-Carbon sugar Ribose • Has bases A, G, C and U • URACIL • A = U; G = C

9. Decoding the Information in DNA • Transcription: process where instructions for making a protein are transferred from a gene (DNA) to an RNA molecule DNA (gene)  RNA (mRNA)

10. Decoding the Information in DNA • Translation: cells use two different types of RNA (rRNA and tRNA) to read the instructions made on mRNA and put together the amino acid that makes up the protein RNA (mRNA)  rRNA & tRNA = Protein

11. Decoding the Information in DNA • Gene expression: entire process by which proteins are made based on information encoded in DNA • Aka: protein synthesis DNA (gene)  RNA (mRNA)  rRNA & tRNA = Protein Transcription Translation

13. Transfer of Information from DNA to RNA • RNA polymerase: enzyme that adds and links complementary RNA nucleotides during transcription

14. Transfer of Information from DNA to RNA • Steps of TRANSCRIPTION: • RNA polymerase binds to the genes promoter • Promoter: specific sequence of DNA that acts as a “start” signal for transcription

15. Transfer of Information from DNA to RNA • Steps of TRANSCRIPTION: • RNA polymerase then unwinds and separates the two strands of the double helix, exposing the DNA nucleotides on each strand

16. Transfer of Information from DNA to RNA • Steps of TRANSCRIPTION: • RNA polymerase adds and then links complementary RNA nucleotides as it “reads” the gene. RNA moves along the nucleotides of the DNA strand that has the gene (only one of the strands). Follows base pairing rules. A = U, G = C

17. Transfer of Information from DNA to RNA

18. Transfer of Information from DNA to RNA • RNA polymerase eventually reaches “stop” signal in DNA • “Stop” is sequence of bases that marks the end of the gene

19. Transfer of Information from DNA to RNA • RNA nucleotides linked by covalent bonds • Behind RNA, DNA strands close (zip) back up • Transcription uses DNA nucleotides as a template • Only part of one strand (the gene) of DNA serves as the template

20. Transfer of Information from DNA to RNA • Prokaryotes: • Transcription occurs in cytoplasm…why? • No nucleus • Eukaryotes: • Transcription occurs in nucleus • During transcription many copies of RNA are made simultaneously from a single gene

21. End of Part 1 http://www.youtube.com/watch?v=ztPkv7wc3yU

22. Section 1: Part 2 http://www.youtube.com/watch?v=5bLEDd-PSTQ

23. The Genetic Code: 3 Nucleotide “Words” • Messenger RNA (mRNA) is made when a cell needs a particular protein • mRNA: form of RNA that carries the instructions for making a protein from a gene and delivers it to the site of translation

24. The Genetic Code: 3 Nucleotide “Words” • Translation: information translated from the language of RNA (nucleotides) to the language of proteins (amino acids) • Codons: RNA instructions are written as a series of 3-nucleotide sequences on the mRNA

25. The Genetic Code: 3 Nucleotide “Words” • Each codon along mRNA strand corresponds to an amino acid or signifies a start or stop signal for translation

26. The Genetic Code: 3 Nucleotide “Words” • Genetic Code: the amino acids and start and stop signals that are coded for by each of the possible 64 mRNA codons

28. Interpreting Genetic Code • Find the first base of the mRNA codon along the left side of the table • Follow that row to the right until you are beneath the second base of the codon • Move up or down in that section until you are even, on the right side of the chart, with the third base of the codon

29. Translation • Translate this mRNA sequence into amino acids:

30. RNA’s role in Translation • Translation takes place in the cytoplasm • Transfer RNA (tRNA): single strands of RNA that temporarly carry a specific amino acid on one end • Each has an Anticodon: a three nucleotide sequence on a tRNA that is complementary to an mRNA codon

31. Example • Transfer this mRNA sequence into its tRNA anticodon and its amino acid • tRNA anticodons: • CAA • UGG • CUA • GUC

32. RNA’s role in Translation • Ribosomes: composed of both proteins and ribosomal RNA • Each ribosome temporarily holds one mRNA and two tRNA molecules • rRNA: RNA molecules that are part of the structure of ribosomes

33. Translation • Lets make a small poster that summarizes the 7 steps of translation!

34. Translation • Step 1: • Translation begins when mRNA leaves nucleus and enters cytoplasm • mRNA, two ribosomal subunits, and tRNA carrying the amino acid methionine form a functional ribosome • mRNA “start” codon AUG, signals beginning of protein chain, is oriented in ribosome in the P site • tRNA molecule carrying methione can bind to the start codon

36. Translation • Step 2: • Codon in the area of the ribosome called the A site is ready to receive the next tRNA • tRNA with complementary anticodon arrives and binds to the codon in the A site • tRNA is carrying its specific amino acid

37. Translation • Step 3: • Both A and P site have tRNA molecules, each carrying an amino acid • Enzymes help form a peptide bond between adjacent amino acids

38. Translation • Step #4: • tRNA in P site detaches • Leaves behind its amino acid, and moves away from the ribosome

39. Translation • Step #5: • tRNA (with its protein chain) in A site, moves to P site • Because anticodon remains attached to codon, tRNA molecule and mRNA molecule move as a unit • Result: new codon is present in A site, ready to receive the next tRNA molecule and its amino acid • Amino acid is carried to A site by a tRNA and then bonded by a peptide bond to the growing protein chain

41. Translation • Step #6: • tRNA in the P site detaches and leaves its amino acid

42. Translation • Step #7: • Steps 2 through 6 are repeated until a stop codon is reached • Stop codon is one of three codons • UAG, UAA, UGA • No tRNA molecule with a complementary anticodon • Because there is no tRNA molecule to fit into the empty A site, protein synthesis stops • Newly made protein is released into the cell

44. RNA’s Role in Translation • Many copies of the same protein are made from a single mRNA molecule • Once ribosome has moved past the start signal another ribosome can come in and start translating

45. RNA’s Role in Translation • Genetic code is nearly universal • With few exceptions the genetic code is the same in all organisms • Evidence for common ancestor

46. SOng The gene is part of the DNA, The gene is TRANSCRIBED by the mRNA, The mRNA goes to the ribosome, rRNA is part of the ribosome, TRANSLATION occurs on the ribosome, tRNA has an anticodon, The anticodon matches to the mRNA codon, The tRNA brings in the amino acid, First to the P then the A site, The amino acids are connected by a peptide bond, And that’s how we make a protein!

47. Review • Lets watch a video of transcription and translation for review! • http://www.youtube.com/watch?v=bpMhgAGybe4&feature=related