Download Gene Expression

Gene Expression
Objectives
1. Be able to describe the types of information coded in DNA.
2. Be able to identify the structural components of RNA.
3. Be able to distinguish RNA from DNA both structurally and functionally.
4. Be able to describe, in order, the steps involved in producing a functional mRNA molecule,
starting with transcription of a protein-coding gene.
5. Be able to explain the roles of rRNA, mRNA, and tRNA in translation.
6. Be able to describe, in order, the steps of translation.
7. Be able to explain what the genetic code is and to explain the significance of key features of
the genetic code.
8. Be able to use a codon chart to relate a DNA sequence to an amino acid sequence (and vice
versa) and to decode mRNA.
9. Be able to distinguish between substitution, deletion, and insertion mutations and explain the
consequences for the polypeptide specified by the mutated DNA.
10. Be able to relate gene expression to an organism’s phenotype.
Terms
N-base
adenine (A)
guanine (G)
thymine (T)
cytosine (C)
uracil (U)
pentose
deoxyribose
ribose
phosphate
nucleotide
complementary bases
DNA
RNA
mRNA
tRNA
rRNA
ribosome
transcription
template
gene
promoter
coding region
terminator
amino acid
protein/polypeptide
genetic code
codon
anticodon
translation
initiation
elongation
termination
mutation
substitution
deletion
insertion
genotype
phenotype
enzyme
biosynthetic pathway
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Procedure 1. Basic Gene Expression
1. Obtain an envelope of molecules and a ribosome from the prep area.
2. The white molecule is a double stranded DNA molecule. Use the chain marked with an “X”
as a template to construct an mRNA molecule with the yellow bases. (This simulation does not
include introns or other control elements.)
3. Get a codon chart from the prep table or use the one in your textbook. Match the seven blue
tRNA anticodons with the appropriate purple amino acids to make charged tRNA molecules.
Remember that the codon chart gives codons, and that you are matching based on anticodons!
4. Align the small ribosomal subunit with the start codon. Match the appropriate charged tRNA
with the anticodon that complements the start codon. Attach the large ribosomal subunit such
that the charged tRNA is in the P site.
5. Find the charged tRNA whose anticodon complements the second codon. Align the tRNA
with the second codon; the tRNA and its amino acid should be in the A site.
6. Gently detach the amino acid from the first tRNA and attach it to left tab of the amino acid in
the A site. Remove the first tRNA from the ribosome. Shift the ribosome so that the remaining
tRNA is now in the P site.
7. Align the third tRNA with the codon that is now in the A site. Gently detach the two amino
acids from the tRNA in the P site and attach them to the left tab of the tRNA in the A site.
Remove the now empty tRNA from the P site of the ribosome, and shift the ribosome to bring a
new codon into the A site.
8. Repeat step 7 until all of the charged tRNA molecules have been matched to codons on the
mRNA. At this point, a stop codon should be in the A site. Match the release factor with the
stop codon to terminate translation.
9. Write your mRNA and amino acid sequences in the space below.
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Review Questions
1. List three structural differences between DNA and RNA.
2. Distinguish between transcription and translation.
3. Describe how a functional mRNA molecule is produced.
4. List the three primary types of RNA molecules and give the function of each.
5. Describe the events of the three stages of translation: initiation, elongation, and termination.
(space to continue on next page)
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6. What is meant by the term genetic code? What are some of the features of the genetic code?
7. Given below is the sequence of a short wild-type protein as well as various mutant forms of
the protein.
a. Describe the general type of mutation in each case.
b. Indicated the specific base-pair change that occurred for each mutation. Assume these
mutations resulted from single base-pair changes. (There may be more than one correct answer).
c. A fourth mutation is identified. The strain carrying this mutation produces abnormally low
amounts of wild-type protein. In what part of the gene is this mutation likely to be located?
Wild-type:
Mutant#1:
Mutant#2:
Mutant#3:
met
met
met
met
trp
trp
cys
trp
tyr
arg
gly
ser
pro
thr
ile
his
val
arg
val
gly
leu
ser
gln
pro
thr
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