Transcription and Translation – Introduction
Transcription and Translation – Introduction
Be sure that you have read over our online lecture this unit on DNA and read pp 177 to 181 in your book before starting. DNA can be a complex concept to grasp, and there is a lot of terminology to keep straight. These first two exercises will focus on transcription and translation, the two processes responsible for taking the information embedded in our DNA and using it to create a protein.
There are segments in our DNA called genes that code for the proteins needed to carry out cellular functions. These genes are a sequence of nucleotides; adenine (A), thymine (T), cytosine (C) and guanine (G) and the specific sequence of these nucleotides is what conveys the information needed to produce a given protein. In humans, the smallest gene is 252 nucleotides long, whereas the largest is more than 2 million nucleotides long! The genetic code is used to decipher the sequence of nucleotides into a sequence of amino acids. The code uses a series of three-nucleotide sequences called codons. Each different codon codes for an amino acid and it is this specific sequence of amino acids that determines what protein is formed.
DNA is found in our nucleus, yet our proteins are synthesized in the cytoplasm. A gene must first be transcribed into a form that can leave the nucleus. Transcription is the process in which a sequence of DNA used to synthesize a complementary strand of messenger RNA (mRNA). This mRNA acts a template and is used to translate the original DNA sequence into a protein, based on the information in its codons and the Genetic Code.
For example, the DNA sequence ATG-CGT-TAG-CGT-ATTC would be transcribed into the mRNA sequence UAC-GCA-AUC-GCA-UAA. Then, using Fig 10.11 on p 180 in your book, you can determine that this mRNA would be translated into the amino acid sequence Tyrosine-Alanine-Isoleucine-Alanine-Stop.
In Exercise 1, you will have the opportunity to demonstrate your understanding of transcription and translation. You will be using the following website; be sure that you are able to access and use the site:
University of Utah. No date. Transcription and Translation
http://learn.genetics.utah.edu/content/molecules/transcribe/ (Links to an external site.)
In Exercise 2, you will apply what you learned in Exercise 1 and evaluate the effect that different types of mutations have on the outcome of transcription and translation. You’ll want to review these mutations on pp 186-187 of your book and in our online lecture on DNA before starting. You will be using the following website; be sure that you are able to access and use the site:
McGraw Hill. No date. Virtual Lab: DNA and Genes
http://www.glencoe.com/sites/common_assets/advanced_placement/mader10e/virtual_labs_2K8/labs/BL_04/index.html (Links to an external site.)
Finally, in Exercise 3, you will complete a series of calculations to determine the probability of a mutation occurring within a gene that results in a change in protein structure.
- UNIT 5 EXPERIMENT ANSWER SHEET Please submit to the UNIT 5 Experiment SUBMISSION LINK no later than Sunday midnight.
SUMMARY OF ACTIVITIES FOR UNIT 1 EXPERIMENT ASSIGNMENT
· Experiment 5 Exercise 1 – Transcription and Translation
· Experiment 5 Exercise 2 – Translation and Mutations
· Experiment 5 Exercise 3 – Mutation Rates
Experiment 5 Exercise 1: Transcription and Translation
This exercise will ensure that you have a good understanding of the processes of transcription and translation. To get started, go to the following website:
University of Utah. No date. Transcription and Translation
http://learn.genetics.utah.edu/content/molecules/transcribe/
Procedure
A. Read over the information on the first screen and click on the click here to begin to proceed.
B. On the next screen transcribe the give DNA strand.
Table 1. Transcription of the DNA sequence (1.5 pts).
RNA
C. Once you have finished transcribing the DNA, you will then translate the RNA sequence. Follow the instructions on the screen.
Table 2. Translation (1.5 pts)
Codon Amino Acid Codon 1 Codon 2 Codon 3 Codon 4 Codon 5 Codon 6
Experiment 5 Exercise 2: Translation and Mutations
Now that you know how to transcribe DNA and translate the mRNA message, let’s take a look at the different types of mutations that might disrupt this process. Review pp 186-187 in your book before beginning. In this exercise you will need to use the following website:
McGraw Hill. No date. Virtual Lab: DNA and Genes http://www.glencoe.com/sites/common_assets/advanced_placement/mader10e/virtual_labs_2K8/labs/BL_04/index.html
Read over the information in the Mutation Guide and close it when you are done. Note that there are several pages; you will need to click on Next to proceed through the Guide. If you want to review this material, you can click on the Mutation Guide button. You are going to run a series of simulations in which an mRNA sequence and its corresponding amino acid sequence is provided. You will be told what type of mutation you will you apply (= Mutation Rule) and you will have to determine the new, mutated mRNA and the resulting protein sequence.
Procedure
A. Click on the Mutate button to get started.
B. Find the Mutation Rule (lower left corner) and enter it into Table 3 below (see the Example provided).
C. Drag the appropriate nucleotides to build the new, Mutated mRNA sequence. If you make a mistake building the new mRNA sequence, drag the correct nucleotide and place it on top of the incorrect one (you cannot actually remove a nucleotide).
D. Once you have generated your Mutated mRNA sequence, you now need to build your Mutated amino acid sequence by matching the appropriate amino acid with each codon. Click on Genetic Code Chart to see the code or you can use Figure 10.11 on p 160 in your book.
NOTE: If you add a STOP codon, do NOT add any more amino acids after it!
E. Once you have finished, click on the Check button. If you are correct, then continue with Step F. If you had errors, you will have to Reset the simulation and start over with Step A. Here is what the results look like for the example provided:
F. When you have been successful, enter the Original mRNA sequence and the Original amino acid sequence in the Table below. Then enter the Mutated mRNA and Mutated protein sequence.
G. Click on Reset and repeat Steps A through F four more times so that you end up with FIVE replicates. Do not reuse the same Mutation Rule and do not use the rule used in the example (“the 4th A becomes a C”). If you get the same Mutation rule twice, Reset the simulation and run again.
Do NOT use the same Mutation rule as shown in the example and do NOT use the same Mutation Rule twice!
Table 3. Mutation rules, mRNA sequences and amino acid sequences (10 pts).
Rep Mutation Rule and Sequences E X
A
M
P
L
E
Mutation rule: The 4th A becomes a C Original mRNA sequence AUG CAC ACG GUG CGA GGG AGU CUG Original amino acid sequence Met (Start) – His – Thr – Val – Arg – Gly – Ser – Leu Mutated mRNA sequence AUG CAC ACG GUG CGC GGG AGU CUG Mutated amino acid sequence Met (Start) – His – Thr – Val – Arg – Gly – Ser – Leu Consequence Substitution appears to have had no effect; Arg Arg 1 Mutation rule: Original mRNA sequence Original amino acid sequence Mutated mRNA sequence Mutated amino acid sequence Consequence 2 Mutation rule: Original mRNA sequence Original amino acid sequence Mutated mRNA sequence Mutated amino acid sequence Consequence 3 Mutation rule: Original mRNA sequence Original amino acid sequence Mutated mRNA sequence Mutated amino acid sequence Consequence 4 Mutation rule: Original mRNA sequence Original amino acid sequence Mutated mRNA sequence Mutated amino acid sequence Consequence 5 Mutation rule: Original mRNA sequence Original amino acid sequence Mutated mRNA sequence Mutated amino acid sequence Consequence
Questions
1. What is a silent mutation? Did you see any examples of this in your mutations above? If so, which mutation rule(s) generated it? Cite your sources (2 pts).
2. What is a missense mutation and how does it differ from a nonsense mutation? Did you see examples of either of these types of mutation and if so, which mutation rule(s) generated it? Cite your sources (2 pts).
3. What is a frame-shift mutation and why are they so damaging? Did you see any examples of this in your mutations above? If so, which mutation rule(s) generated it? Cite your sources (2 pts).
4. Find a genetic disorder that develops as a result of one of the types of genetic mutations we have examined in this exercise. Identify the disorder and briefly describe the mutation responsible. Cite your sources (3 pts).
Experiment 5 Exercise 3: Mutation Rates
We learned in our second exercise that not all mutations have an observable effect. Yet the risk of a mutation being damaging is fairly significant, so it is important to understand the probability of them occurring. In this exercise, we are going to calculate the probability of a mutational event within a gene. You are given the necessary information below to complete the calculations. Do not let them overwhelm you; this is simple math, so think things through.
Assume that:
· there are approximately 3,000,000,000 base pairs in the mammalian genome (genes constitute only a small portion of this total)
· there are approximately 10,000 genes in the mammalian genome
· a single gene averages about 10,000 base pairs in size
Questions
1. Based on the assumptions above, in the mammalian genome, how many total base pairs are in all the mammalian genes? Show your math (2 pts).
2. What percentage (%) of the total genome does this represent? Show your math (2 pts).
3. What is the chance (%) that a random mutation will occur in any given gene? Show your math (2 pts).
4. Only 1 out of 3 mutations that occur in a gene result in a change to the protein structure. What is the probability that a random mutation will change the structure of a protein? Show your math (2 pts).
UNIT 1 Experiment Grading Rubric
Component Expectation Points Experiment 5 Exercise 1 Demonstrates an understanding of the process of transcription and translation (Table 1 and 2). 3 pts Experiment 5 Exercise 2 Correctly implements the proper mutation and transcribes the mRNA correctly (Table 3). 10 pts Demonstrates an understanding of the different types of mutations and their consequences (Questions 1-4). 9 pts Experiment 5 Exercise 3 Correctly calculates the necessary information (Questions 1-4). 8 pts TOTAL 30 pts
1. Explain the four roles that DNA plays in cells? How are these roles influenced by DNA’s structure? Be sure you demonstrate your understanding of DNA’s structure in your answer.
Citation(s):
2. Match the terms with the most suitable description. _____ genetic code a. Examples of RNA processing _____ promoter b. Sequence of three nucleotides that code for an amino acid. _____ exon c. Location on DNA where RNA polymerase attaches. _____ intron d. Sequence of three nucleotides that is complementary to a codon triplet. _____ anticodon e. Portion of a gene that is excised from the RNA transcript. _____ codon f. Rules that convert a nucleotide sequence into a protein. _____ cap and tail g. Parts of a gene that are expressed.
3. Briefly explain the differences among messenger RNA, transfer RNA and ribosomal RNA in terms of the roles they play in transcription and translation and where they are found in the cell.
Citation(s):
4. Using the genetic code table (Fig 10.11 on p 180), take the following DNA sequence and complete the following. Note that the mRNA is generated from the complementary DNA strand. T A C C C C A T G T A A C A T A C C A C T
Complementary DNA strand _______________________________________________
mRNA strand ___________________________________________________________
Amino acid sequence _____________________________________________________
5. Part of the coding sequence of a gene produces an mRNA sequence of A U G A A G G C U C C U C C A A G C G G C
What is the DNA sequence __________________________________________________
What is the amino acid sequence _____________________________________________
6. Review pp 178-185 in your book and view the following animation. Then complete the following table. You may need to watch it the video more than once to catch the details.
Genome British Columbia. Gene Expression. 2007. Web. 25 July 2016. https://www.youtube.com/watch?v=OEWOZS_JTgk (Links to an external site.)
Question Transcription Translation What is it, in brief? Where does it occur in the cell? What is the product? Describe how the product is modified to reach its final form. Citation(s):
Updated April 2015
