1. Essential Idea Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.

2. Understandings Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase. Translation is the synthesis of polypeptides on ribosomes. The amino acid sequence of polypeptides is determined by mRNA according to the genetic code. Codons of three bases on mRNA correspond to one amino acid in a polypeptide. Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.

3. Skills and Applications Skill: Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid. Skill: Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence. Skill: Deducing the DNA base sequence for the mRNA strand.

4. RNA and Protein Synthesis DNA, RNA, Protein Synthesis & GENES

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6. IB Assessment Statement Compare the structure of RNA and DNA. Copyright Pearson Prentice Hall

7. DNA, RNA, PROTEIN SYNTHESIS & GENES Genes are coded DNA instructions that control the production of proteins. Genetic messages can be decoded by copying part of the nucleotide sequence from DNA into RNA. RNA contains coded information for making proteins.

8. The Structure of RNA RNA consists of a long chain of nucleotides. Each nucleotide is made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base.

9. The Structure of RNA There are three main differences between RNA and DNA: 1. The sugar in RNA is ribose instead of deoxyribose. 2. RNA is generally single-stranded. 3. RNA contains uracil in place of thymine.

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11. DNA vs. RNA Copyright Pearson Prentice Hall

12. Types of RNA There are three main types of RNA: 1. messenger RNA 2. ribosomal RNA 3. transfer RNA

13. Types of RNA Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.

14. Types of RNA Ribosomes are made up of proteins and ribosomal RNA (rRNA). Ribosome Ribosomal RNA

15. Types of RNA During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome. Amino acid Transfer RNA

16. 3.5.2 Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase. Copyright Pearson Prentice Hall

17. Transcription RNA molecules are produced by copying part of a nucleotide sequence of DNA into a complementary sequence in RNA. This process is called transcription. Transcription requires the enzyme RNA polymerase.

18. Transcription During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.

19. Practice Base Pairing of DNA to mRNA DNA Template Strand Complementary RNA Strand Adenine A Thymine T Guanine G Cytosine C A A G T C Uracil U Adenine Cytosine Guanine U G C A U

20. Transcription Summary During Transcription, only one strand of DNA double helix serves as a template for the synthesis of mRNA. The strand of DNA that is the template for mRNA is called the antisense. The strand of DNA that is NOT a template for mRNA is called the sense strand. RNA polymerase binds only to regions of DNA known as promoters. Promoters are signals in DNA that indicate to the enzyme where to bind to make RNA.

21. This model illustrate the process of transcription that takes place in the nucleus. The DNA base sequence of the gene is copied into messenger RNA (mRNA) 1.The DNA helix is opened at the position of the gene. 2.The helix is unwound by RNA polymerase 3.RNA nucleotides are found in the nucleus space. 4.One of the DNA chains act as a template for mRNA Copyright Pearson Prentice Hall

22. This model illustrate the process of transcription that takes place in the nucleus. The DNA base sequence of the gene is copied into messenger RNA (mRNA) 5.Free nucleotides base pair with DNA nucleotides 6.The phosphodiester bonds on the mRNA chain are formed by RNA polymerase 7.mRNA is a single polynucleotide chain but the base thymine is replaced by Uracil. Copyright Pearson Prentice Hall

23. This model illustrate the process of transcription that takes place in the nucleus. The DNA base sequence of the gene is copied into messenger RNA (mRNA) 8After the mRNA is complete the molecule detach's from the DNA and leaves the nucleus for the cytoplasm ribosomes. 9The DNA helix reforms. Copyright Pearson Prentice Hall

24. Transcription RNA RNA polymerase DNA

25. IB Assessment Statement Describe the genetic code in terms of codons composed of triplets of bases. Copyright Pearson Prentice Hall

26. The Genetic Code The genetic code is the “language” of mRNA instructions. The code is written using four “letters” (the bases: A, U, C, and G).

27. The Genetic Code A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.

28. The Genetic Code Each codon specifies a particular amino acid that is to be placed on the polypeptide chain. Some amino acids can be specified by more than one codon.

29. The Genetic Code

30. There is one codon AUG that can either specify the amino acid methionine or serve as a “start” codon for protein synthesis. There are three “stop” codons that do not code for any amino acid. These “stop” codons signify the end of a polypeptide.

31. Practicing Translation from mRNA to Amino Acid mRNAAmino Acid AUG CCC AGG GGA GCA AGC AGU Methionine Proline Arginine Glycine Alanine Serine

32. More on the genetic code: The genetic code: A polynucleotide is a sequence of bases Bases are either A T G or C There are 4 bases which operate in sets of 3 (a triplet).= 4 3 possible triplets of DNA =64 triplets There are 20 common amino acids Therefore 64 triplets are mapped to 20 amino acids However there is a 'punctuation' triplets. Therefore the mapping of the code is 64: 21 Copyright Pearson Prentice Hall

33. The genetic code is first transcribed into mRNA The mRNA codons can be mapped to a specific amino acid. The mapping is 64 triplets: 64 codons: 21 DNA is a degenerate code since there are more than one triplet or codon that maps to an amino acid or punctuation. mRNA codon AUG codes for Methionine and is a START signal for translation. mRNA codon UAA, UAG, UGA are all stop codons punctuating the code. GGU, GGC, GGA and GGG all code for amino acid glycine. Copyright Pearson Prentice Hall

34. IB Assessment Statement: Explain the process of translation, leading to polypeptide formation. Copyright Pearson Prentice Hall

35. Translation Translation is the decoding of an mRNA message into a polypeptide chain (protein). Translation takes place on ribosomes. During translation, the cell uses information from messenger RNA to produce proteins.

36. Translation Nucleus mRNA Messenger RNA is transcribed in the nucleus, and then enters the cytoplasm where it attaches to a ribosome.

37. Translation Translation begins when an mRNA molecule attaches to a ribosome. As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA. In the ribosome, the amino acid is transferred to the growing polypeptide chain from the cytoplasm.

38. Translation Each tRNA molecule carries only one kind of amino acid. In addition to an amino acid, each tRNA molecule has three unpaired bases. These bases, called the anticodon, are complementary to one mRNA codon.

39. The Structure and Function of Transfer RNA A C C A tRNA molecule consists of a single RNA strand that is only about 80 nucleotides long Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a cloverleaf

40. LE 17-14a Amino acid attachment site Hydrogen bonds 3 5 Two-dimensional structure Anticodon Amino acid attachment site 3 5 Hydrogen bonds Anticodon Symbol used in this book Three-dimensional structure 35 Because of hydrogen bonds, tRNA actually twists and folds into a three-dimensional molecule tRNA is roughly L-shaped

41. Translation Lysine tRNA Phenylalanine Methionine Ribosome mRNA Start codon The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA.

42. Ribosomes Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)

43. tRNA Ribosome mRNA Lysine Translation direction 3’3’3’3’ 5’5’5’5’

44. Protein Synthesis (building a polypeptide): Ribosomes are the site of polypeptides synthesis. This involves linking amino acids together through condensation (dehydration) reactions. tRNA Ribosome mRNA Lysine Translation direction 3’3’3’3’ 5’5’5’5’

45. Elongation of the Polypeptide Chain At the ribosome, amino acids are added one by one to the preceding amino acid A peptide bond is formed between the amino acids.

46. Translation The process continues until the ribosome reaches a stop codon. Polypeptide Ribosome tRNA mRNA

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48. Translation more details: Location of Translation: The location of translation is the ribosomes in the cytoplasm. Ribosomes are also composed of RNA (rRNA) which acts as a catalyst for the translation of the mRNA. Free ribosomes form polypeptides (proteins ) for internal cell use. Ribosomes on the endoplasmic reticulum synthesis proteins for secretion. Copyright Pearson Prentice Hall

49. Translation more details: Step 1: mRNA from the nucleus locates onto the ribosome. The start codon (initiation codon) AUG occupies one of two rib some site. In this image the second site is occupied by CUG codon. The ribosome moves along the mRNA Copyright Pearson Prentice Hall

50. Translation more details: Step 2: Activation is a process in which Transfer RNA (tRNA) molecules attach to specific amino acids. The tRNA molecule an anti-codon, three bases that are complementary to the codons on mRNA. In heterotrophs the amino acids for activation come form consumed protein in the diet. Copyright Pearson Prentice Hall

51. Translation more details: Step 3: The first codon (AUG) bonds to the tRNA anti-codon UAC. This tRNA carried the amino acid Methionine. The second tRNA (GAC) binds to the second site with mRNA codon CUG The second tRNA carried the amino acid Leucine. Note that codon-anticodon binding is antiparallel Copyright Pearson Prentice Hall

52. Translation more details: Step 4: The link between the tRNA and the amino acid Methionine is broken. The bond energy is transferred to form a peptide bond between methionine and Leucine. The first tRNA is released form the ribosome first site. This tRNA molecule moves away to pick up more methionine. Copyright Pearson Prentice Hall

53. Translation more details: Step 5: The ribosome move one mRNA codon to the right (in this image). mRNA now occupied site one on the ribosome The mRNA codon is UGC which has the complementary tRNA of ACG and is charged with Serine. This occupied site site on the ribosome. Copyright Pearson Prentice Hall

54. Translation more details: Step 6: The ribosome move one mRNA codon to the right (in this image). mRNA now occupied site one on the ribosome The mRNA codon is UGC which has the complementary tRNA of ACG and is charged with Serine. This occupied site site on the ribosome. Copyright Pearson Prentice Hall

55. Translation more details: Step 7: The bond between tRNA and Leucine is broken. The bond energy is transferred to form a peptide bond between Leucine and Serine. The tRNA for leucine is released form site one. Then ribosome shift to the right and the process repeats itself until the stop codon is encountered. As the amino acid chain is built the polypeptide self assembles into the correct shape. It essentially folds up due to intra-molecular forces such as hydrogen bonds. Copyright Pearson Prentice Hall

59. Genes and Proteins The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein. Codon mRNA Alanine Arginine Leucine Amino acids within a polypeptide Single strand of DNA

60. http://www.wiley.com/legacy/college/boyer/ 0470003790/animations/translation/transl ation.htm https://www.youtube.com/watch?v=itsb2Sq R-R0 Copyright Pearson Prentice Hall

61. IB Assessment Statement Discuss the relationship between one gene and one polypeptide. Originally, it was assumed that one gene would invariably code for one polypeptide, but many exceptions have been discovered. Copyright Pearson Prentice Hall

62. Genes and Proteins Genes contain instructions for assembling proteins. Many proteins are enzymes, which catalyze and regulate chemical reactions. Proteins are each specifically designed to build or operate a component of a living cell.

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64. One Gene One Polypeptide: Theory: One gene is transcribed and translated to produce one polypeptide. Some proteins are composed of a number of polypeptides and in this theory each polypeptide has its own gene. e.g. haemoglobin is composed of 4 polypeptides (2 of each type) and there is a gene for each type of polypeptide. This theory, like so many in biology has exceptions. e.g. 1) Some genes code for types of RNA which do not produce polypeptides. 2) Some genes control the expression of other genes. Copyright Pearson Prentice Hall

65. Animation on one gene one polypeptide: http://www.youtube.com/watch?v=Thj6jq7 mYkE Copyright Pearson Prentice Hall

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