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WebLab5: Exercise2
Translation: Using the Genetic Code to Construct Protein
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Objectives:
- Explain why the genetic code is called a "triplet" code.
- Explain the role of m-RNA, r-RNA, and t-RNA in protein synthesis.
- Given a chart of the genetic code and a sequence of RNA bases, construct a polypeptide's primary structure.
- Construct the primary structure of a polypeptide before and after a point mutation.
- Define amino acid, polypeptide, protein, ribosome, polyribosome, codon, anticodon.
- Describe what is meant by a protein's primary, secondary, tertiary, and quarternary structure.
- Explain how a single amino acid substitution in a protein could result in that protein being non-functional or dysfunctional.
- Why are t-RNA molecules often referred to as "adaptors?"
- Explain the three phases of translation: initiation, elongation, and termination.
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Materials:
- A computer, a printer, and an ISP (Internet Service Provider).
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Methods:
- Read the Background Information
to help prepare you for the content of this exercise.
- The following webpage from Brooklyn College: Physical
Structure, The Giant Molecules of Life -Proteins presents
the information you just read in greater depth, and includes illustrations
that will help you to visualize amino acids and how they link
to each other forming proteins. Be sure to observe the animation
at the end of the exercise: You Explore: Make a Dipeptide.
- Go to the
Translation Site entitled "What is a Gene?" from
the University of Utah. Read the review of transcription presented
briefly on this webpage (considered in our previous WebLab) before
studying the description of translation.
- Scroll to the section entitled: "Build a Protein." As you work
through the animation, you will review transcription of RNA from
a DNA template. You will then learn how to translate RNA's genetic
code into a sequence of amino acids.
- Answer the following questions based on your study of the site
and, in particular, your observations of the chart of the Genetic
Code.
- Write out the letters for the "start" codon found coded
in m-RNA molecules. Which amino acid is coded for by the "start"
codon? Does this mean that all proteins always begin with
the same amino acid?
- Write out the letters for the "stop" codon. Is there only
one? Do the stop codons actually code for particular amino
acids?
- Would it be accurate to say that each of the twenty amino
acids is coded for by one and only one codon? Defend your
answer using examples from the chart of the genetic code.
- Complete the exercise presented at this site involving the folding
of paper and the writing of DNA's code, then a m-RNA code, and
finally an amino acid sequence. This sheet will be submitted in
class.
- For submission to your professor, complete the simulation at
the end of the
"What is a Gene" webpage, just above the guide questions.
HAVE PAPER AND PENCIL HANDY. In this simulation you construct
a m-RNA molecule and then construct a small polypeptide. Now,
carry out the following modifications to the genetic code in this
simulation:
- Create a mutation. This will be a substitution: cause the
ninth nucleotide base on the m-RNA to change from a G to a
C. Use the genetic code to write out the new amino acid sequence
for the polypeptide.
- Now create a different type of mutation. This one is called
a deletion: eliminate the ninth nucleotide base on the m-RNA;
G just disappears. Write out the amino acid sequence for this
polyepetide.
- This time mutate the second m-RNA base from G to A, and
the third m-RNA base from C to U. What is the resulting polypeptide
in this case?
- Go to the Translation, Part
2 page for further background information about translation.
- Go to The
Translation Animation site and see protein synthesis in motion!
Once the animation starts, control the motion (stop and start)
using your mouse on the knob at the extreme left of the bottom
control bar.
- An animation that runs a bit slower than the one above may be
seen at this
second Translation Animation Site.
- Go to the web page entitled From
RNA to Proteins (part of the Molecular Biology Notebook,
online) to observe diagrams and to review the concepts explained
in the last section. After looking at and studying the graphics,
watch the short movie on translation.
- Answer the following questions based on your study of this weblab
and the links provided. Submit these in class with your answers
to the items in 5, 6, and 7, above.
- Explain why the genetic code is called a triplet code.
- What do the codons UGG and AUG have in common?
- Explain all the structures and molecules to which t-RNA
binds.
- Use a real example, or create a hypothetical situation,
and explain how a mutation could make a person ill.
- As in the previous question, explain how a mutation could
make a person function in a superior manner.
- Submit the answers to the questions from this WebLab to me
in class.
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