Translation: From RNA to Protein

1. Translation:From RNA to Protein SBI 4U November 19th, 2012

2. Agenda Take up homework Lesson on transcription

3. Open your Notebooks, and respond to the following questions Describe the process of initiation What is the difference between the coding strand and the template strand? What is the function of the spliceosomes?

4. Recall mRNA has left the nucleus (after the transcription process)

6. The Ribosome mRNA in cytoplasm – ready for translation Ribosomes attach to mRNA – 5’ cap 2 subunits: 60S & 40S Subunits clamp mRNA in 5’ to 3’ direction – growing polypeptide chain One nucleotide at a time – each codon codes for 1 amino acid

7. The Role of Transfer RNA (tRNA) tRNA delivers amino acids to polypeptide building site 2 “arms” – 1 arm, anticodon recognizes codon of the mRNA . 2nd arm carries corresponding amino acid Recognition by tRNA of mRNA is facilitated by the complementarity of base pairing – UAU is AUA Every tRNA carries 1 amino acid only

8. The Role of Transfer RNA (tRNA) Aminoacyl-tRNA– tRNA molecule containing its corresponding amino acid attached to its acceptor site

9. Elongation of the Polypeptide Chain Start codon: AUG – ensures that the correct reading frame is used by the ribosome AUG – methionine Ribosome has 2 sites for tRNA: Acceptor (A) site and Peptide (P) site

10. Elongation of the Polypeptide Chain Peptide site: when peptide bonds are formed between adjoining amino acids on a growing polypeptide chain Acceptor site: site in the ribosome where tRNA brings in an amino acid

11. Steps in the Elongation of the Polypeptide Chain Methionine – P site Next tRNA carrying amino acid enters A site Ribosome shifts over one codon Third amino acid enters A site and second moves over to P site All 3 amino acids bonded by a peptide bond

12. Termination of Protein Synthesis Stop codon 3 stop codons: UGA, UAG, UAA No corresponding tRNAs Release factor: protein that recognizes that the ribosome has stalled and aids in the release of the polypeptide chain from the ribosome 2 subunits fall of mRNA and translation is done

13. Debate Groups Genetically Modified Foods For: Against: Cloning For: Against: Gene Therapy For: Against:

14. Debate Groups Genetic Screening For: Against:

15. Remember … Please hand in a typed copy of your debate presentation. Each group will hand in one copy Hand in your references with the typed copy. References should be in APA format

16. Structure of Debate • Opening Statements, by each group. Affirmative speaks first. • Like an introduction to a formal paper, introduce yourself/team and the topic you will be debating. Tell what you are going to argue during the debate (like a thesis statement) and tell why your position should win. • Oral Arguments • Like the body of a formal paper, present the evidence that proves your position is correct. This argument should be very factual and persuasive. Opinions not backed by facts could be used to show the weakness of your case, so be careful! • Rebuttal Arguments • Presentment of counter evidence that shows: false, inaccurate, misrepresented, or weak points in the opposition’s argument.

17. Structure of Debate, cont’d • Cross Examinations • As each team finishes its rebuttal, the other team has time to ask questions about the evidence presented in order to prove the invalidity of the argument. • Closing Arguments • Like the closing paragraph of a formal paper, summarize the key points you presented. Conclude with a persuasive argument that will win the debate for you even if you are losing based on facts!

18. Homework HIV Case Study: pg 249 Page: 254, q: 1, 2, 4, 6

19. Homework: HIV Case Study No HIV cannot attach itself to a muscle or skin cell. HIV’s antigens are not complementary to the binding sites (receptors) of skin cells and muscle cells 3. Reverse transcriptase uses RNA as a template and builds a complementary DNA strand, thereby transcribing RNA into DNA. Reverse transcriptase is an appropriate name for the enzyme, given that conventional transcription of genetic material is in the direction of DNA to RNA. In this case, RNA is transcribed into DNA, meriting it the label of reverse transcription

20. 4. If a helper T cell divides and viral DNA has been incorporated into the cell’s genome, it will also be replicated and be present in both of the daughter cells 5. HIV can stay dormant for many years before symptoms are exhibited in its carrier, therefore an individual can be infected with HIV but not necessarily show any symptoms 6. People who are infected with HIV usually die of another infection because HIV attacks helper T cells, which are part of a human’s immune system. Helper T cells act as guards against invading pathogens. Since HIV destroys helper T cells, the body cannot launch an immune response to secondary infections such as pneumonia.

21. 8. Antibiotics and other drugs are specifically designed to target a specific virus. The drugs must recognize the virus to be effective. Drugs recognize viruses by the protein particles that they carry on their outer membrane. If a virus mutates, it is possible that the protein found on its outer membrane will be affected and change shape. If protein conformation changes, the drug may no longer be able to recognize the virus and therefore will become inneffective

22. Translation Answers (a) The A and P sites are found in a ribosome that is translating an mRNA sequence into protein. The A (acceptor) site is where tRNA molecules bring in the appropriate amino acid. The P (peptide) site is where peptide bonds are formed between adjoining amino acids on a growing polypeptide chain (b) A codon is a triplet of ribonucleotides on mRNA that encodes a single amino acid. An anticodon is a triplet of ribonucleotides on tRNA that recognizes and pairs with a codon on the mRNA

23. (c) The start codon signals to the ribosome to start synthesizing the polypeptide chain. The start codon is always AUG and codes for methionine. The stop codon signals to the ribosome to stop the process of translation. The stop codons are UGA, UAG, and UAA 2. The three types of RNA are mRNA, tRNA and mRNA. Messenger RNA represents the product of transcription of a gene. It encodes the sequence of triplet codons that will be read by the ribosomes to build proteins. It also encodes the start and stop codons that ribosomes use to initiate and terminate translation. Transfer RNA delivers amino acids to the ribosome, which are used to build proteins during the process of translation. Each amino acid has a corresponding transfer RNA. Ribosomal RNA binds with ribosomal proteins to form ribosomes.

24. 4. An error in the third base of a codon in mRNA may not necessarily result in an error during the process of translation because more than one codon encodes a particular amino acid. The codons differ by the third nucleotide. For example: proline can be encoded by the codons CCU, CCC, CCA, and CCG. If a mistake is made in the third nucleotide of the codon, it is negligible. It does not matter what the nucleotide is – the two first nucleotides CC, will always code for proline. The possibility of flexibility in the third nucleotide of a codon is termed the wobble hypothesis

25. 6. The genetic code must be used. AUG is always the start codon and encodes for the amino acid methionine: 5’-GGC-CCA-UAG-AUG-CCA-CCG-GGA-AAA-GAC-UGA-GCC-CCG-3’ Met-Pro-Pro-Gly-Lys-Asp-Stop