Download Protein Synthesis Instructions

Protein Synthesis
Instructions
The purpose of today’s lab is to:
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Understand how a cell manufactures proteins from amino acids, using information stored in the genetic
code.
Assemble models of four very short proteins based on four mRNA sequences.
Identify several types of mutations and to evaluate their impact on protein synthesis.
Successfully use the genetic code to reverse-engineer a protein with a specific function.
The structure and operation of the human body (as well as all other organisms) is based on proteins. Everything
from skin and bones to hair, muscle and internal organs are constructed from proteins. The enzymes that digest food
and the hormones that regulate metabolism are all proteins. Although some of these compounds are highly
specialized and have additional materials associated with them (e.g., calcium found in bone tissue), all have proteins
as their foundation.
Activity 1. Translating Messenger RNAs
Materials
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Protein synthesis kit. This kit consists of 24 amino acids, 24 transfer RNAs, four messenger RNAs and one
ribosome (see below).
anticodon
tRNA
ribosome
amino acid
mRNA
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Codon conversion table (attached)
Procedure
1.
Pair up your tRNA molecules with the
appropriate amino acids (see image on
right for help).
tRNA
amino acid
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2.
Chain initiation.
Insert the 5’ end of an mRNA into the ribosome until the first codon (AUG) is exposed in the peptidyltRNA binding site. Select the tRNA with an anticodon that base-pairs with the exposed codon and join it
to the mRNA.
3.
Chain growth.
a.
The next codon is exposed in the amino acyl-tRNA binding site. Again, select an appropriate tRNA
with its attached amino acid and join it to the mRNA.
b.
The amino acid (or peptide) that is presently joined to the tRNA at the peptidyl-tRNA binding site is
separated from the tRNA and joined instead to the amino group of the amino acid positioned at the
amino acyl-tRNA binding site. The result is a peptide bond between the two amino acids. The free
tRNA is released from the peptidyl-tRNA binding site and floats away.
c.
The ribosome now slides down the mRNA three nucleotides exposing the next codon in the amino
acyl-tRNA binding site.
d.
Repeat steps a-c until the “protein” is synthesized (you reach the end of the mRNA). Note: There are no
stop codons on these mRNAs!
4.
Record the amino acid sequences for this “protein” in the observation section of the report.
5.
Repeat this procedure with the other three mRNAs.
6.
Answer the questions in the lab report.
7.
Return all parts to the envelope and return to the instructor’s bench.
Answer Questions 1-11 on the Lab Report.
Activity 2. Designer Proteins
Note: This activity uses a DNA-to-amino acid conversion table (also attached).
1.
Follow the instructions on the laptop activity.
2.
Try to get up through Challenge #2 on the third page of the activity. This challenge will ask you to design a
protein that can “catch” a positively-charged ion.
3.
You will first need to determine which amino acids your protein will have, and then you will have to reverseengineer a DNA sequence that encodes this information.
Answer Question 12 on the Lab Report.
There is no need to print anything from the laptop, nor do you have to answer any of the questions in the
activity.
4.
If you would like to continue with the laptop activity beyond Challenger #2, please feel free to do so. (There is
only one more page afterwards.)
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mRNA sequence ➞ Protein sequence
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DNA sequence → Protein sequence
1
3
amino acid
properties
DNA codons
A
Ala
alanine
hydrophobic
GCA GCC GCG GCT
C
Cys
cysteine
hydrophobic
TGC TGT
D
Asp
aspartic acid
acidic (–)
GAC GAT
E
Glu
glutamic acid
acidic (–)
GAA GAG
F
Phe
phenylalanine
hydrophobic
TTC TTT
G
Gly
glycine
hydrophobic
GGA GGC GGG GGT
H
His
histidine
basic (+)
CAC CAT
I
Ile
isoleucine
hydrophobic
ATA ATC ATT
K
Lys
lysine
basic (+)
AAA AAG
L
Leu
leucine
hydrophobic
TTA TTG CTA CTC CTG CTT
M
Met
methionine
hydrophobic
ATG
N
Asn
asparagine
hydrophilic
AAC AAT
P
Pro
proline
hydrophobic
CCA CCC CCG CCT
Q
Gln
glutamine
hydrophilic
CAA CAG
R
Arg
arginine
basic (+)
AGA AGG CGA CGC CGG CGT
S
Ser
serine
hydrophilic
AGC AGT TCA TCC TCG TCT
T
Thr
threonine
hydrophilic
ACA ACC ACG ACT
V
Val
valine
hydrophobic
GTA GTC GTG GTT
W
Trp
tryptophan
hydrophobic
TGG
Y
Tyr
tyrosine
hydrophobic
TAC TAT
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Protein Synthesis
Lab Report
Name ________________________________________
Activity 1. Translating Messenger RNAs
1.
For each of your four mRNAs, fill in the nucleotide and corresponding amino acid sequences below.
mRNA 1 sequence
Protein 1
mRNA 2 sequence
Protein 2
mRNA 3 sequence
Protein 3
mRNA 4 sequence
Protein 4
2.
Compare protein 2 to protein 1. Does the amino acid sequence of protein 2 differ from the sequence of protein
1? If yes, which amino acid(s) differ?
3.
Compare mRNA 2 to mRNA 1. Does the codon sequence of mRNA 2 differ from the codon sequence of
mRNA 1? If yes, which codons differ?
4.
Note that the second amino acid is the same in both proteins, even though their codons are different. Write all
of the codons that can code for that specific amino acid.
_____________________________________________________________________________________________
5.
Where does the amino acid sequence of protein 3 differ from the sequence of protein 1?
6.
Where do the codons of mRNA 3 differ from mRNA 1?
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7.
Compare protein 4 to protein 1. Where does the amino acid sequence of protein 4 differ from the sequence in
protein 1?
8.
Where does the codon sequence of mRNA 4 differ from mRNA 1?
9.
A frameshift mutation is caused by either an insertion or deletion of bases that results in the displacement in the
coding region of a gene. Assume that mRNA 1 is the “normal” (wild-type) version of this gene. Which of the
other mRNAs displays a frameshift?
____________________________________________
10. Where has the frameshift occurred in this mRNA? ________________________________________________
11. What has been the effect of this frameshift on the amino acid sequences of these two mRNAs?
Activity 2. Designer Proteins
12. In the space below, write out the DNA sequence, mRNA sequence, and amino acid sequence of the protein you
designed to catch the positively-charged ion.
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