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Senanu's Bio class

Chapter 16.1 - 16.2 – How genes work

The reading assignment for today is split between part of chapter 16 and part of chapter 17. We will look at a general overview of how genes work, and then focus on the process of transcription.

OBJECTIVE: Understand the general framework of the central dogma

  1. What is the one-gene-one-enzyme hypothesis?
  2. Look at the results for the experiment described in figure 16.2. Why did the mutants with the arg1 mutation require ornithine? Use the ‘Interpretation’ part of the box to help you understand.
  3. Why could the arg1 mutants grow with additional arginine?

  4. Put the following words in order, according to the central dogma: mRNA, protein, DNA. Once they are in order, connect them with arrows labeled as: translation, transcription.

    OBJECTIVE: Be able to identify how DNA mutations affect an individual’s phenotype

  5. Explain how a DNA mutation could affect coat color in mice (Fig 16.4). Make sure you use al the steps of the central dogma to explain this.

Chapter 17.1 - 17.2 – Transcription and RNA processing

OBJECTIVE: Be able to describe and apply the process of transcription and connect transcription to metabolism and energy use.

  1. Where in the cell does transcription occur?
  2. What is the end product of transcription?
  3. What is the end product of translation?
  4. What is the name of the DNA region to which the RNA polymerase binds in order to initiate transcription?
  5. Look at Figure 17.1. Free incoming NTPs have ____ phosphate groups. After being joined in the phosphodiester linkage, they only have _____. Is this reaction spontaneous? (This process is the same for the polymerasation of DNA and RNA)
  6. What enzyme constructs the mRNA molecule?
  7. What are the 3 phases of transcription?
  8. In prokaryotes, how does the RNA polymerase know where to begin transcribing? Draw this in a diagram.
  9. In bacteria, what signals the RNA polymerase to stop transcribing?
  10. What do you think would happen if you deleted 3 base pairs in the TATA box of a eukaryotic gene? How might that affect the individual’s phenotype?
  11. To which end of the mRNA molecule are nucleotides added?
  12. How do the four bases of RNA pair up with four bases of DNA (A, T, C, G) when the mRNA is constructed?
  13. To which end are dNTPs added to DNA?
  14. To which end are NTPs added to RNA?
  15. Which strand of DNA gets transcribed? The coding or template strand?
  16. Why do you think the non-template strand also called the ‘coding’ strand?

  17. Why do you think transcription factors are an important part of the transcription ‘machinery’?

    OBJECTIVE: Understand RNA processing in eukaryotes

  18. What is added to the 5’ end of mRNA? Why?
  19. What is added to the 3’ end of mRNA? Why?
  20. What is an intron? An Exon?
  21. Where does the mRNA go to after processing?
  22. Compare the length of DNA to the length of processed (mature) mRNA in eukaryotes? What makes the DNA longer than mRNA? What increases the length of mRNA relative to DNA?
  23. Go to the website https://www.ensembl.org/index.html In the search box at the top right, search for “SHANK3”. Click on the first result “SHANK3 (Human gene)” and look at the diagram of the gene. The boxes represent exons and the bent lines represent introns. Click on the red gene that is labeled “SHANK3-201 > Protein coding”. How many exons are there?
  24. This map is to scale and is typical of eukaryotic genes. What does this tell you about the relative size of introns vs exons?
  25. What is the main function of a spliceosome?
  26. List one reason why alternative RNA splicing may lead to new proteins over evolutionary time.