Chapter 13- RNA and Protein Synthesis

1. Chapter 13- RNA and Protein Synthesis Mr. Bragg 2013-2014

2. 13.1 Essential Question- What is RNA? • Describe how RNA differs from DNA • Explain the functions of RNA • Describe how cells synthesize RNA

4. I. 13.1 RNA • The Role of RNA • How does RNA differ from DNA? • RNA- is a nucleic acid that consists of long chains of nucleotides • Made up of a 5 carbon sugar, a phosphate group, and nitrogenous bases

5. c. Comparison- key differences DNA • Sugar is deoxyribose • Is double stranded • Contains thymine RNA • Sugar is ribose • Is single stranded • Contains uracil instead of thymine

6. 2. Role Analogy • Builders use plans to build a home • DNA = the master plan – too valuable to bring to the job site • RNA = blueprint- inexpensive and disposable • The master plan is used to prepare the blueprints

7. 3. Functions of RNA • Major job- protein synthesis • Controls the assembly of amino acids into proteins

8. c. The 3 different types of RNA • Messenger “m” RNA • Ribosomal “r” RNA • Transfer “t” RNA

9. d. Roles of the 3 Types of RNA • mRNA- carry information from DNA to other parts of the cell • rRNA- make up the subunits of the ribosome; worktable for making protein • tRNA- carries amino acids to the ribosome and matches them to the coded mRNA message

10. B. RNA Synthesis • How does the cell make mRNA? • Transcription – segments of DNA serve as templates to produce complimentary RNA molecules • The base sequences of transcribed RNA complement the base sequences of the DNA template

11. In prokaryotes, transcription takes place in the cytoplasm • In eukaryotes, it takes place in the nucleus

12. Transcription requires an enzyme- RNA polymerase • RNA polymerase binds to DNA and separates the 2 strands • Next, it uses one strand of DNA to make a template in RNA • One gene can produce 100’s-1,000’s of RNA molecules MIT – Lego Transcription

13. b. Promoters • RNA polymerase bonds only to promoters • This tells RNA polymerase where to start and stop transcription • Promoters are signals in the DNA molecule’s sequence Transcription animation

14. c. RNA editing • RNA molecules require some editing before being read • Introns- the pieces that are edited out of the pre-mRNA molecule • Exons- the remaining pieces after the pre-mRNA molecule has been edited

15. 13.1 Essential Question- What is RNA? • Describe how RNA differs from DNA • Explain the functions of RNA • Describe how cells synthesize RNA

16. 13.2 Essential Question- How do cells make proteins? • Describe how the genetic code is read • Explain the role of ribosomes in assembling proteins • Describe the “central dogma” of molecular biology

17. II. 13.2 Ribosomes and Protein Synthesis • The Genetic Code • What is the genetic code, and how is it read? • First step- transcribe the base sequences from DNA to RNA • RNA then must be translated into polypeptides, which form proteins

18. c. Polypeptides- a long chain of amino acids that makes protein • There are 20 amino acids commonly found in proteins • The properties of a protein depend on the order in which the amino acids are assembled

19. The 4 bases (A, U, C, G) in RNA form a “language” • These bases form the genetic code • The sequence of bases is read a codon at a time • Codons contain 3 bases • Each codon specifies a single amino acid to be added to the polypeptide chain

20. 2. How to Read Codons • There are 4 different bases in RNA, which means there are 64 possible codons • 4 x 4 x 4 = 64 possibilities

21. Most amino acids can be specified by more than one codon • Ex: Leucine can be coded for in 6 ways: UUA, UUG, CUU, CUC, CUA, and CUG • Genetic code tables are used to decode codons

22. 3. Start and Stop Codons • AKA the “punctuation marks” of the genetic code • The methionine codon AUG = start • mRNA is then read 3 bases at a time until it reaches a “stop” codon. • Once stopped the polypeptide is complete

23. B. Translation (p. 368 – 369) • What role does the ribosomes play in assembling proteins? • Analogy: putting together a complex toy • Need to read the directions AND put the parts together • Ribosomes carry out these tasks in a cell Lego Translation Translation animation

24. Ribosomes use the sequence of codons in mRNA to assemble amino acids into polypeptide chains • Translation – the decoding of the mRNA message into protein

25. 2. Steps in Translation • Transcribed mRNA from the nucleus moves into the cytoplasm to attach to a ribosome • Codons pass through the ribosome and tRNAs bring the proper amino acids into the ribosome • Each tRNA molecule carries just one kind of amino acid

26. tRNA has 3 unpaired nitrogen bases = anticodon • So, each tRNA anticodon is complimentary to one mRNA codon • Ex: tRNA anticodon is UAC, the mRNA codon is AUG

27. d. Like an assembly-line worker that attaches one part to another, the ribosome helps form a peptide bond between the amino acids e. The chain continues to grow with each tRNA coming in until it reaches the “stop” codon on mRNA f. The ribosome then releases the protein and the mRNA

28. 3. The Roles of tRNA and rRNA in Translation • All 3 major forms of RNA work together to make protein synthesis occur • mRNA brings the DNA message out of the nucleus • The tRNA deliver the amino acid called for by the mRNA • The rRNA are part of the ribosome and help locate the “start” code of the mRNA message

29. C. The Molecular Basis of Heredity • What is the central dogma of molecular biology? a. Information is transferred from DNA to RNA to protein

30. Summary b. Protein has everything to do with how genes are expressed • Ex: A gene that codes for an enzyme to produce pigment can control the color of a flower c. Gene expression – the way in which DNA, RNA, and proteins are involved in putting genetic information into action in living cells d. It’s universal!

31. 13.2 Essential Question- How do cells make proteins? • Describe how the genetic code is read • Explain the role of ribosomes in assembling proteins • Describe the “central dogma” of molecular biology

32. 13.3 Essential Question- What happens when a cell’s DNA changes? • Describe what a mutation is • Explain how mutations affect genes

33. III. 13.3 Mutations • Types of Mutations • What are mutations? a. From Latin “mutare”- meaning to change b. Defined: any heritable change in the genetic information c. Two types • gene • chromosome

34. 2. Gene Mutations a. Point mutations – mutation where a single or very few nucleotides are changed • Include substitutions, deletions, and insertions • Usually occur during replication of DNA

35. b. Substitutions • One base is changed to a different base • Usually affect no more than a single amino acid • Sometimes have no effect at all Analogy: Original The fat cat ate the wee rat. Point Mutation The fat hat ate the wee rat.

36. c. Insertions and deletions • One base is either inserted or removed from the DNA sequence • Effects can be dramatic • Can lead to frameshift mutations Analogy 1: Original The fat cat ate the wee rat. Frame Shift The fat caa tet hew eer at. Analogy 2: Original The fat cat ate the wee rat. Insertion The fat cat xlw ate the wee rat.

37. 3. Chromosomal Mutations • Involve changes in the number or structure of chromosomes • Can change the location of genes or even the number of chromosomes b. Different types • Deletion, duplication, inversion, translocation Animation link

38. B. Effects of Mutations • How do mutations affect genes? • Genetic information can be altered by natural events or by artificial means • Fact: Incorrect bases are routinely copied during DNA replication at a rate of 1/10,000,000

39. 2. Mutagens • defined: chemical or physical agents in the environment • Chemical examples: pesticides, plant alkaloids, tobacco smoke, pollutants • Physical examples: radiation like X-rays and UV light

40. 3. Harmful and Helpful Mutations • The effects of mutations on genes vary widely. • Some have little effect • Some are beneficial • Some negatively disrupt gene function • Most have little or no effect b. Effect is situational c. Can generate variability within a species

41. d. Harmful effects • The most harmful effects come when the structure of a protein is dramatically changed • These can disrupt normal body routines • Can result in genetic disorders • Ex: Cystic Fibrosis

42. e. Beneficial Effects • Sometimes mutations can produce proteins with new or altered functions that can be useful to an organism in a changing environment • Ex: mutations have allowed certain insects to be resistant to pesticides – like mosquitoes • Plant and animal breeders make good use of mutations

43. Non-disjunction in plants during meiosis can be a beneficial mutation • Leads to the formation of polyploid plants • Plants can be triploid or tetraploid • Ex: bananas, citrus, sugarcane, grains, etc… Strawberries are octoploid 8N = 56 2N = 7

44. Mutations in Mammals Siamese cat- the protein that produces fur color is dependent on heat. This is caused by a mutation in one gene White Appaloosa horse- color is caused by a mutation in one gene

45. Mutations in “Herps” Leucistic alligator, three legged frog

46. tomatoes Seedless grapes

47. 13.3 Essential Question- What happens when a cell’s DNA changes? • Describe what a mutation is • Explain how mutations affect genes

48. 13.4 Essential Question- How do cells regulate gene expression? • Explain how genes are regulated in prokaryotic and eukaryotic organisms • Describe the controls placed on the development of tissues

49. IV. 13.4: Gene Regulation and Expression • How are genes regulated? • In prokaryotes DNA binding proteins regulate genes by controlling transcription • 2. Genes are organized into operons: groups of genes that are regulated together

50. On the operon are regulatory regions • Promoters – site where RNA polymerase binds for transcription • Operators – site where a DNA binding protein can attach; analogy: car boot Gene expression animation