BIO181 Transcription Translation Worksheet2

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Arizona State University *

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Biology

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Feb 20, 2024

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BIO181 Transcription Translation Worksheet If any questions are unanswered, you will receive a score of 0. The extension questions are required . Name: Michael Pasek Class Time: 10:30 Part 1: Transcription ______________________________________________________________________________________ READ THIS : DNA is often referred to as a genetic blueprint. In the same way that blueprints contain the instructions for construction of a building, the DNA found inside the nuclei of cells contains the instructions for assembling a living organism. The DNA blueprint carries its instructions in the form of genes. In most cases the genes direct the production of a polypeptide, from which other more complex proteins, such as enzymes or hormones, may be constructed. These polypeptides and other molecules run the organism’s metabolism and, in multicellular organisms, dictate what each cell’s job is. So, what is the language of these instructions and how are they read and decoded by the cellular organelles? This activity will focus on the decoding of genes in eukaryotes. ______________________________________________________________________________________ Note - These are the same images. The image on the left is provided as a Google drawing. To edit it, draw on it, add circles or labels to it, double click the image while in Google Docs. Add in what you need to, then hit “Save and Close”. The image on the right is clearer but cannot be edited. 1. Refer to Model 1. a. What is the base-pair rule for a DNA strand matching an RNA strand? C to G T to A A (DNA) to U (RNA) b. Compare this base-pair rule with that of two DNA strands. DNA does not contain uracil, to T matches to A and A matches to T in DNA. However in DNA/RNA match, T bonds with A and A bonds with U 1

2. Which strand of the DNA contains the “blueprint” for the pre-mRNA? Template strand 3. Consider Model 1 a. In which direction is the DNA template strand read? 3’ to 5’ b. The DNA template strand and pre-mRNA strand are anti-parallel. With this in mind label the 3ʹ and 5ʹ ends of the pre-mRNA strand in Model 1. TCAGCCAUUACAUGGAU c. In which direction is the pre-mRNA molecule constructed? On which end are new bases added? 5’ to 3’ _______________________________________________________________________________________ READ THIS: In eukaryotes the enzyme RNA polymerase joins with several transcription factor proteins at the promoter, which is a special sequence of base pairs on the DNA template strand that signals the beginning of a gene. The transcription factor proteins, along with the RNA polymerase, is called the transcription initiation complex . This moves along the DNA template strand at about 40 base pairs per second producing pre-mRNA. When the RNA polymerase reaches the terminator sequence of base pairs on the DNA template strand, it completes the production of pre-mRNA and releases it into the nucleoplasm. _______________________________________________________________________________________ 4. Where on the DNA strand does the transcription initiation complex form? It forms on the promoter 5. Imagine the diversity of functions in which your cells participate. a. Do you think that the cells in your big toe contain the same DNA as the neurons in your brain? Yes all the cells in your big toe contain the same DNA as the neurons in our brain b. Will an individual cell transcribe every, or almost every, gene in its genome? Explain. No, cells only transcribe genes as they are needed to make specific proteins. No certain genes will be switched on in specific cells and switched off in others depending on the location and function of the cell its coding for. 2

Note - These are the same images. The image on the left is provided as a Google drawing. To edit it, draw on it, add circles or labels to it, double click the image while in Google Docs. Add in what you need to, then hit “Save and Close”. The image on the right is clearer but cannot be edited. 6. Compare the pre-mRNA to the mRNA leaving the nucleus in Model 1. a. What has been removed from the pre-mRNA to make it into mRNA? The introns have been removed b. What has been added to the mRNA that was not present in the pre-mRNA, and where on the mRNA strand are the additional items located? A methyl cap has been added to the 5’ end of the mRNA and a poly-A tail has been added to the 3’ end of the mRNA 7. Can mRNA diffuse through a membrane? Why or why not? mRNA can diffuse through a membrane through membrane nanotubes and not by diffusion. 3

______________________________________________________________________________________ READ THIS: Introns are sections of pre-mRNA that are noncoding. That is, they don’t provide useful information for the production of the polypeptide being synthesized. There is evidence that suggests these introns allow certain sections of DNA to code for different polypeptides when different sections are removed. The removal of specific sections is triggered by a signal response in the cell. The portions of the pre-mRNA that remain are called exons . The methyl cap (sometimes called the GTP cap or 5ʹ cap) helps the mRNA molecule move through the nuclear pore and attach to a ribosome, its final destination. mRNA is a short lived molecule. Once in the cytoplasm the mRNA will be subject to exonucleases that immediately start removing individual nucleotides from the 3ʹ end of a nucleic acid. The individual mRNA nucleotides will then be free to be used again during the process of transcription. ______________________________________________________________________________________ 8. The human genome contains about 25,000 genes and yet produces about 100,000 different polypeptides. Propose an explanation of how this is possible. A single sequence of pre-mRNA can produce different mRNA sequences depending on what introns are removed 9. Using the information in Read This section , develop a hypothesis to explain the advantage of the poly-A tail added to the 3’ end of the mRNA. The advantage of the poly-A tail added to the 3’ end of the mRNA is that it prevents the information-carrying part of mRNA from being destroyed by the exonuclease before a polypeptide can be formed. 10.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? Justify your answer. An mrna with at short tail will have a shorter lifespand. If mRNA has a longer tail it will have a longer lifespan. Proteins that are needed over long periods of time might come long-tail mRNA’s where proteins that are only needed briefly can come from short tailed mRNA. 11.Summarize the steps of transcription. Pre-mRNA is made from the template strand of DNA starting at the promoter by the transcription initiation complex. When the RNA polymerase reaches the terminator, the pre-mRNA is released. Introns are removed and the methyle cap and poly-A tail are added to make mRNA. Part 2: Translation 4

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