Download Assignment 4

Astrobiology, Fall 2005
Exercise 4
Protein Synthesis (From
Gene to Protein)
Name: ____________________
OBJECTIVES
In this exercise, you will
 Use paper models of DNA, mRNA, tRNA, and amino acids to simulate protein synthesis and produce
a “polypeptide chain”
 Through the simulation exercise, you should come to understand the relationship between the
simulated molecules
 Ultimately, by the end of the exercise you should understand how a cell synthesizes a polypeptide
chain from a genetic sequence of DNA
INTRODUCTION
Protein synthesis is a critical series of reactions performed by living cells to produce the proteins
essential for life. Basically, the process involves transcription of a genetic sequence of DNA into a
complementary mRNA strand, and then translation of the mRNA strand by tRNA and ribosomes (and, of
course enzymes) to produce a chain of amino acids (polypeptide chain) which is then modified into a
protein. The transcription of an mRNA strand is based on complementary base-pairing of DNA and
mRNA nucleotides (based on the “rules of base pairing”), and the translation of mRNA is based on
complementary base-pairing of codons of mRNA and anticodons of tRNA.
Hopefully, in class, you have discussed in more detail, the processes and molecules involved in
protein synthesis. This exercise will serve as a simulation of the processes. You will simplify transcription
and translation by simply utilizing paper models of DNA, mRNA, tRNA, and amino acids. For simplicity
the role of enzymes and ribosomes will be left out. They are however, critical to actual protein synthesis in
cells. Before continuing with this exercise, make sure that you are familiar with the processes of protein
synthesis, complementary base-pairing, and the genetic code.
MATERIALS (per group)
Paper models of DNA, mRNA, tRNA, amino acids
A DNA genetic sequence
PREPARATION
Before working with this simulation you should have a basic understanding of the concepts of
transcription and translation.
PROCEDURE
1.
2.
3.
4.
Work in groups of 3 or 4.
Obtain an envelope of molecules and a genetic sequence
Cut your molecules free of the 8-1/2” x 11” sheet (if not already)
Construct the sense strand of your DNA molecule (using the DNA molecules labeled “DNA” on the
back)
5. Construct the anti-sense strand of your DNA molecule (using the DNA molecules labeled “
” on the
back). You should now have a double-stranded DNA molecule.
6. Simulating transcription, “unzip” your DNA molecule and construct an mRNA strand through
complementary base-pairing with the sense strand. Do this as the cell does, one mRNA at a time.
7. When the mRNA strand is complete, remove it from the DNA sense strand and “zip” up your DNA
8. Activate your tRNA molecules by binding them to their specific amino acid molecules.
9. Simulating translation, use the appropriate tRNA molecules to construct the polypeptide chain.
This is accomplished by base-pairing the codons of the mRNA strand to the complementary anticodon
of the tRNA molecules. This should be done in order, just as the cell does it. You can use the genetic
code library of your textbook or the one provided with the lab.
10. Bind the amino acids of adjoining tRNA molecules to create the polypeptide chain.
11. Record you results in Table 1 below.
DATA
Table 1: Molecules (and sequences) of Protein Synthesis
Transcription
DNA nonsense strand
DNA sense strand
mRNA strand
Translation
mRNA strand (codons)
tRNA anti-codons
Amino acid sequence
QUESTIONS
1.
Briefly describe what happens in transcription. What is needed for the process and what is made?
2. What is a codon?
3. What is the role of tRNA in translation? What is an anti-codon?
4. How does an mRNA molecule specify where the polypeptides it encodes should begin? How does it
specify where the polypeptide should end?
5.
After the process of translation, what has been made?
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