Gene Expression Activity
PSI Biology
Name__________________________
Background
A gene is a segment of DNA needed to make a specific protein.
The shapes of proteins are determined by the sequence of their amino acids.
Proteins must be "coded" with the correct sequence of amino acids to have the right
shape. Gene expression is the process of translating the "code" in the nucleic acid
and producing the protein.
Gene expression occurs whenever a specific protein is needed by the cell.
This process requires:
•
Producing a messenger RNA from the DNA template in the nucleus
•
Transferring the mRNA to the ribosome
•
At the ribosome, using the messenger RNA molecule, along with transfer RNA
molecules to attach amino acids in the correct primary sequence to produce the
desired protein.
Question 1: What messenger RNA molecule would be produced from this DNA
template strand?
3' TAC GGC TTC CCC CTA ACT 5' template (parent) strand
5' _______ _______ _______ ______ _______ _______
3'
new messenger RNA molecule
The mRNA "message" is read in 3-base letter codons.
Codons each contain one of three different “messages”
1. Start translation (AUG/Methionine is always the first amino acid in a
sequence)
2. Bring X amino acid (61 codons)
3. Stop translation (3 codons: UAA, UAG, and UGA)
Question 2: If UCU codes for serine and CCU codes for proline, “translate” this
messenger RNA molecule: AUG CCU UCU UAA
_________________________________________________________________________________________________
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Use this chart of amino acids and their
corresponding codons to answer the next
questions. This is known as the universal
genetic code because all organisms from
the smallest bacteria to the largest tree or
animal utilize the same code to produce all
cellular proteins.
Question 3: Bradykinen is a polypeptide
that causes smooth muscles to relax and
blood vessels to dilate, which reduces
blood pressure.
The sequence of amino acids that comprise
this polypeptide are:
Met-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg.
Working backwards, construct the messenger RNA sequence that would code for
this polypeptide: (Include a stop codon)
Met-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg
5' ______-_______-_______-______-_______-________-________-______-_______-_______-_______ 3'
Question 4:
From the messenger RNA molecule produced in question 4, produce the DNA molecule.
template strand
3' ______ _______ _______ ______ _______ ________ ________ ______ _______ _______ _______ 5'
non-template strand
5' ______ _______ _______ ______ _______ ________ ________ ______ _______ _______ _______ 3'
Part 2: It is possible for the DNA or RNA molecule to replicate incorrectly. Mistakes
are termed mutations. What are some possible consequences of mutations?
Question 5:
Suppose during the replication of the following DNA molecule, the base in red was
replicated incorrectly:
5' AAT TCG CCC CGT TTA 3' non-template strand
3' TTA AGC GCG GCA AAT 5' template strand
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What messenger RNA would be produced from this new strand?
5' _____________ _____________ ____________ _____________ ___________3'
Question 6:
Referring to the messenger RNA molecule in question 6, how would the mutation
affect the protein produced from this section?
_________________________________________________________________________________________________
Question 7:
Suppose a mutation resulted in the following messenger RNA section.
The mutated section is highlighted in yellow:
5' AGU AGG CGG CGU UUG 3'
Here is the correct mRNA section:
5' AGU AGG CGA CGU UUG 3'
How will this mutation affect the resulting polypeptide?
_________________________________________________________________________________________________
Question 8: Glucagon is a peptide that raises the level of glucose in the blood.
The amino acid sequence is:
His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-Asn-Thr
What are two completely different messenger RNA sequences that would code for
this amino acid sequence? (Change at least one letter for each amino acid.)
Answer 1: 5' _________ ________ ________ _______ _______ ______ ________ ________ _______
_______
________ ________ ________ _______ _______
______ ________ ________ _______ _______
______ ________ ________ _______ _______
______ ________ ________ _______ 3'
Answer 2: 5' _________ ________ ________ _______ _______ ______ ________ ________ _______
_______
________ ________ ________ _______ _______
______ ________ ________ _______ _______
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______ ________ ________ _______ _______
______ ________ ________ _______ 3'
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Part 3:
Each codon on mRNA corresponds to the anticodon loop section of the tRNA
molecule that brings the amino acid to the ribosome. The transfer RNA molecules
line up in the appropriate order coded for in the mRNA molecule. As the amino
acids are released from the tRNA molecules and joined together, the polypeptide is
elongated.
Question 9: What are the corresponding transfer RNA anticodons that would
attach to the messenger RNA molecule created in question 8?
Answer: Messenger RNA molecule used
5'_____________________________________________________________________________________________3'
Transfer RNA codons:
Question 10: Build your own DNA model.
Using the information from previous questions, construct a three-dimensional
model of a possible gene from DNA that would code for glucagon.
Rules:
1. Cannot use a pre packaged "kit". Instead use everyday materials such as
candy, buttons, or beads.
2. Must be three-dimensional.
3. Label the sugars, phosphates, and all bases. Include a legend.
4. Be sure to arrange each side with a 5’ and 3’ end.
5. Must code for glucagon.
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