Download Lab - Week One: The Scientific Method

Principles of Biology Lab
Fall, 2006
Lab Eight: Central Dogma and Mutation - Worksheet
Central Dogma & Mutation - Pair Worksheet
Pair Names:
In the lab, each pair of students will be given a long piece of genetic material. Complete the following
exercises using this piece of genetic material.
I. Central Dogma Part One - Replication
a) What kind of macromolecule is this? How do you know?
b) Replicate the molecule you have been given to form a DOUBLE HELIX by carefully writing in
chalk below the template the sequence of the replication product (make letters same size as the
molecule given to you). Given the complexities of real replication, we will not be modeling unwinding,
leading/lagging strand, etc. today. Have your instructor check your work before proceeding.
II. Central Dogma Part Two –Transcription
In the lab, continue to use the long piece of genetic material that you replicated earlier. Complete the
following exercises using this piece of genetic material.
a) What kind of macromolecule is this? How do you know?
b) Find the promoter - what enzyme would look for and bind here to begin transcription?
Transcribe this gene by carefully writing in chalk above the template the sequence of the
transcription product (make letters same size as the molecule given to you). Have your instructor
check your work before proceeding.
c) What kind of macromolecule is this? How do you know?
d) What is the specific name of the macromolecule you have just synthesized?
III. Central Dogma Part Three –Translation
Begin your simulation of translation by locating your pair’s ribosome, tRNAs (square post-it notes), polar
amino acids (rectangular yellow post-it notes), and non-polar amino acids (rectangular grey/purplish post-it
notes).
a) “Synthesize” the number of tRNAs that your pair will need to form complementary base pairs to
each triplet in your transcription product. What is the name of the nucleotide triplet in the
tRNA?
In the transcription product?
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b) “Synthesize” a pool of amino acids by writing the three letter abbreviation for each polar amino
acid on a separate rectangular yellow post-it note and each non-polar amino acid on a separate
rectangular grey/purplish post-it note. (A table of polar and non-polar amino acids will be
provided for each table). charging tRNAs with the correct amino acid, and aligning
tRNA/amino acids where they would base pair with the mRNA transcript.
c) Find the first AUG and place your ribosome above it.
d) “Charge” the correct tRNA with its amino acid, using Figure 17.5 to determine which amino acid
should be attached to this tRNA. (Charging the tRNA is completed by sticking a rectangular
small post-it onto the side of a tRNA post-it note opposite the nucleotide triplet on the tRNA.)
Place the charged tRNA on the correct site on the ribosome, and repeat for this process for
the second tRNA. Have your instructor check your work before proceeding.
e) Form the bond between the first two amino acids of your polypeptide by transferring the amino
acid from the first tRNA to the amino acid on the second tRNA. The correct product has the
first tRNA’s amino acid bonded to the side of the second tRNA’s amino acid that is farthest
from the second tRNA’s nucleotide triplet.
f) What is the name of the bond that has just been formed?
Have your instructor check your work before proceeding.
g) Just as the ribosome does in the cell, eject the now uncharged first tRNA, slide the ribosome
down to the next nucleotide triplet of the mRNA, shifting the second tRNA to the site of the
ribosome previously occupied by the first tRNA. Have your instructor check your work before
proceeding.
h) Repeat steps h) through j) until you reach a stop signal or the end of your mRNA. Though you
will not simulate these steps, it is at this point that a releasing factor occupies the A site on
the ribosome, causing the ribosomal subunits to dissociate, thereby releasing the mRNA and the
completed polypeptide.
f) What is the sequence of the polypeptide you have synthesized?
i)
After examining your polypeptide, would you expect to find this polypeptide in a polar or a nonpolar environment in the cell?
j)
Explain the basis for your answer to the last question.
IV. Central Dogma Part Four – Mutation
1. Return to your pair’s original long piece of genetic material. Simulate a spontaneous mutation by
locating the first occurrence of the sequence CTC and changing it to CTT. Make any changes this
would cause in the base sequence of your transcription product.
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a.
Will this mutation change the amino acid sequence of your polypeptide?
b. Write the sequence of the new polypeptide:
c. Has the polar vs. non-polar nature of your polypeptide changed?
d. In what way?
2. Repeat step 1 in this section by changing the CTT sequence you produced to CAT. Make any
changes this would cause in the base sequence of your transcription product. Does this mutation
change the amino acid sequence of your polypeptide?
a. Make this change to your polypeptide by, if necessary, replacing one or more of the amino acids in
your polypeptide.
Write the sequence of the new polypeptide:
b. Has the polar vs. non-polar nature of your polypeptide changed?
c. In what way?
In step 2. you have generated the mutation that causes sickle-cell disease. Use your text and the
Internet to answer the following questions about this disease.
a. What protein is mutated in sickle cell disease?
b. How many amino acids long is this protein?
c. What change is generated in the polar vs. nonpolar nature of this protein by the mutation?
d. How does this change affect the function of the protein?
e. What symptoms are caused by this mutation?
f. What is the demographics of sickle cell disease?
g. Describe any advantageous side effects of having this mutation.
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