NOTES Gene Expression ACP Biology, NNHS

Transcription

1 Name Date Block NOTES Gene Expression ACP Biology, NNHS Model 1: Transcription the process of genes in DNA being copied into a messenger RNA 1. Where in the cell is DNA found? 2. Where in the cell does transcription take place? 3. What enzyme is required for transcription? (HINT: Enzyme names usually end in ase.) 4. Does the enzyme move in one direction or two directions? 5. What polymer (long chain) is synthesized during transcription? 6. What monomers (single units) are used to construct this polymer? 7. Is DNA double or single stranded? 8. Is RNA double or single stranded? N. Berg, NNHS Page 1

2 9. What are the four bases found in DNA? 10. What are the four bases found in RNA? 11. When a DNA strand has an A what base is opposite it on the growing RNA strand? 12. When a DNA strand has a T what base is opposite it on the growing RNA strand? 13. When a DNA strand has a C what base is opposite it on the growing RNA strand? 14. When a DNA strand has a G what base is opposite it on the growing RNA strand? 15. If a DNA strand reads A T C G G A, then what would the transcribed RNA read? CRITICAL THINKING: 16. Nearly all cells in an organism contain identical DNA, and each DNA strand may contain hundreds or thousands of individual genes. Is it likely that a cell would transcribe all the genes within its nucleus at same time? 17. Considering the many types of cells in a multicellular organism, and their different functions, is it likely that all cells transcribe all their genes at some point in their lifetime? Page 2

3 Model 2: mrna Processing Non-coding regions; they do not provide instructions for a protein. Coding regions; they do provide instructions to make a protein. 18. What are the coding regions of the RNA called? 19. What are the non-coding regions of the RNA called? 20. Before the mrna strand can exit the nucleus, it must be processed. Compare the pre-mrna strand to the mrna strand that is leaving the nucleus. a. What has been removed from the pre-mrna to make it into mrna? b. What has been added to the 5 end of the mrna? c. What has been added to the 3 end of the mrna? 21. The mrna leaves the nucleus through what structure? 22. The nucleotides on the mrna will be later read by a ribosome. What sequence of bases indicates the starting point of the instructions? CRITICAL THINKING: 23. The m in mrna is short for messenger. Why is this molecule called messenger RNA? Page 3

4 Read This! The methyl 5 cap helps the mrna molecule move through the nuclear pore and attach to a ribosome. mrna is a short-lived molecule. Once in the cytoplasm the mrna will be subject to exonucleases that immediately start to remove individual nucleotides from the 3 end of a mrna. The free nucleotides will then be free to be used again during transcription. 24. What are the two jobs of a methyl 5 cap? 25. What do exonucleases do to the mrna in the cytoplasm of the cell? CRITICAL THINKING: 26. What is the advantage of the poly-a tail added to the 3 end of the mrna? 27. Different mrna molecules can have poly-a tails of different lengths. Considering the purpose of adding the poly-a tail (from the previous question), why are some tails longer than others? Page 4

5 Model 3: Translation the process of the ribosome reading and carrying out instructions on mrna in order to build a protein. Codon 28. What do the letters U, C, A, and G in Model 3 represent? 29. What do the abbreviations such as Cys, Ala, and Gly in Model 1 represent? 30. How many nucleotides make up a single codon? 31. What amino acid does UUU code for? 32. How many different codons code for the amino acid Proline (Pro)? 33. Compare all of the codons for Proline (Pro). a. How are these codons similar? b. How are these codons different? CRITICAL THINKING 34. Considering that mistakes can occur during transcription, what advantage is there for an organism to have multiple mrna sequences code for the same amino acid? Page 5

6 Codon 35. How does the ribosome know when the instructions for making the protein begin? 36. How many start codons are there? 37. According to the codon chart, what amino acid is at the beginning of every protein? 38. How does the ribosome know when the instructions for making the protein are done? 39. How many stop codons are there? 40. Using the codon chart above and complementary base pairing rules during transcription, complete the following: DNA: T A C C T T C G G A T G G T C A C T mrna: Protein: (chain of amino acids) Page 6

7 Model 4: The Whole Picture How to make a protein. Nuclear membrane transferrna (trna) brings amino acids to the ribosome Ribosome reads the instructions on the mrna and builds the protein Cell membrane 41. What organelle reads the mrna and builds the protein? 42. What molecule brings amino acids to the ribosome? Page 7