Name ____________________________
Period _______
Protein Synthesis Paper Lab
Part A: RNA Structure
Besides ensuring the exact replication of
chromosomes, the order of the bases is a genetic
code of instructions for the cell. How does the
cell “read” the chemical message coded in its
DNA?
Part of the answer lies with a second molecule
present in cells called ribonucleic acid (RNA).
RNA is similar to DNA in that it is made of
nucleotides. However, there is no deoxyribose
or thymine in RNA. Deoxyribose is replaced
by ribose in RNA, and thymine is replaced by
uracil. If you look at their structural formulas
and models, you will see that ribose and uracil
are similar to the molecules they replace.
Part B: RNA Transcription
Open (unzip) one of your DNA models
between the base pairs and separate the
two halves. Using the left side of your DNA
model as a pattern, match up the proper
RNA nucleotides with the DNA nucleotides.
You have made a messenger RNA molecule.
4. Do the RNA half-rung bases pair exactly as
they would if this were DNA replication? _____
Remove the RNA nucleotide series from the DNA
pattern. Close the DNA molecule back up with its
original right side. DNA molecules “unzip”
temporarily during RNA transcription and then
zip closed again.
mRNA is a single-stranded molecule. Thus, the
sequence of RNA nucleotides formed from DNA
represents a complete mRNA molecule. After its
formation, this mRNA leaves the nucleus and goes
to where the ribosomes are. It carries the DNA
message of base sequences in the exact same order
out of the nucleus and into the cytoplasm.
On this table compare DNA and RNA, check all
that apply:
Part C: Structure of tRNA
DNA
Deoxyribonucleic Acid
Ribonucleic Acid
Contains the sugar deoxyribose
Contains sugar ribose
1 a. Which base is replaced by uracil in RNA?
___________________________
2 b. What molecule replaces deoxyribose in
RNA?
___________________________
3. To which base in DNA do the following RNA
bases pair?
Guanine ______________________
Contains a phosphate group
Contains adenine
Contains thymine
Contains uracil
Contains guanine
Contains cytosine
Monomers are nucleotides
Double-strand molecule
Adenine ______________________
C
T
G
A
G
C
Single-strand molecule
Cytosine ______________________
Leaves/moves out of the nucleus
Uracil ________________________
Contains a chemical code
mRNA
Build a molecule of RNA using the paper models.
Join the nucleotides in this order: (new strand!)
Guanine
Adenine
Cytosine
Uracil
Cytosine
Guanine
sequence (anticodon) that attaches to the mRNA.
The amino acid attaches to the tRNA at the
opposite end from the anticodon. Fit the proper
amino acids onto your two tRNA molecules.
4. Which amino acid connects to the tRNA
molecule with the anticodon: (see chart)
a. AGC _______________________
Remember that the molecules of messenger RNA
(mRNA) leave the nucleus and join the cell’s
ribosomes in the cytoplasm. Other molecules
called transfer RNA (tRNA) are also present in
the cytoplasm. Molecules of tRNA are composed
of many nucleotides, just like mRNA, but the
difference is this: tRNA folds so that a three base
sequence (called an anticodon) sticks out and can
match up with a three base sequence on the
mRNA. Look at the paper models provided.
1a. Name the four nitrogen bases present in the
nucleotides of the tRNA molecule:
b. CUG _______________________
5. How many nucleotide bases on the mRNA
molecule are responsible for the coding of
one amino acid? _______________
Part D: Building a Protein (Translation)
As the amino acid molecules are brought to the
mRNA by the tRNA molecules, the amino acids
join to form a protein molecule. This process is
called translation, because the DNA message has
been translated into a protein.
Use the table to answer the questions below.
1b. Do these bases differ from those in mRNA?
Amino acid
1c. How does the shape and structure of tRNA
compare to mRNA?
Join the tRNA molecules to the mRNA that you
built at the beginning.
2. What base in tRNA can only join with the:
a. adenine base of mRNA _________________
serine
proline
leucine
glutamic acid
tyrosine
arginine
glutamine
phenylalanine
valine
lysine
aspartic acid
tRNA
anticodon
AGC
GGG
AAU
CUC
AUA
GCU
GUU
AAA
CAC
UUU
CUG
mRNA
codon
UCG
CCC
UUA
GAG
UAU
CGA
CAA
UUU
GUG
AAA
GAC
b. uracil base of mRNA ___________________
6. What amino acid is attached to a tRNA
molecule having a base sequence of
c. guanine base of mRNA _________________
a. UUU _____________________
d. cytosine base of mRNA _________________
3. What order of bases on mRNA will match a
sequence on tRNA of:
a. UUA (uracil, uracil, adenine) ______________
b. UCA (uracil, cytosine, adenine) ____________
c. UGA (uracil, guanine, adenine) ____________
d. AAA (adenine, adenine, adenine) __________
Any given tRNA molecule can only pick up one
kind of amino acid, depending on the three base
b. GCU _____________________
7. What tRNA anticodon is needed to join with
the following amino acids?
a. phenylalanine ________________
b. valine ______________________
c. glutamic acid _________________
Depending on the number, type and order of
amino acids, an almost endless variety of proteins
can be produced. Because of the repeated
matching of the base sequences, the base sequence
in the DNA of chromosomes codes for and
controls the formation of proteins at the
ribosomes.
8. A protein molecule contains the following
amino acid sequence: leucine, glutamine,
tyrosine, leucine, serine, serine. What would be
the sequence of tRNA bases responsible for
forming this protein?
9. A ribosome receives the following mRNA
message: AAA CGA GAA GUU.
a. What will be the sequence of tRNA bases
matching up with the mRNA molecule?
b. What will be the sequence of amino acids
formed from this code?
To review: You should now be able to transcribe
(decode) a message in DNA base code (triplet)
into mRNA, and then translate it into an amino
acid sequence. Let’s try it. A portion of DNA on
a chromosome has the sequence of bases along
one strand as indicted in the table below.
Transcribe this message first into mRNA code,
then into the tRNA code, and finally translate it
into the correct amino acid sequence.
DNA code
mRNA code
(codon)
tRNA code
(anticodon)
amino acids
AAT
GGG
ATA
AAA
GTT
Every now and then errors may occur in the
process of forming proteins from the DNA coded
instructions. An error is a mutation, which will
result in a different amino acid sequence. The
protein may be different in a good way or (more
frequently) a bad way.
Hemoglobin is the protein in red blood cells that is
responsible for carrying oxygen. There are 600
amino acids in this relatively small protein
molecule, and in most people the amino acids are
all arranged correctly. There is a very slight
change in the amino acid sequence that results in
the very serious disease known as sickle cell
disease. The normally soft and flexible red blood
cells become distorted into a rigid sickle shape and
they form “logjams” in the smallest capillaries,
with disastrous consequences.
The following amino acid sequence represents a
portion of a normal hemoglobin molecule:
proline, glutamic acid, glutamic acid, lysine.
10. Translate the normal amino acid sequence
into:
a. tRNA base code ________________________
b. mRNA base code _______________________
c. DNA base code _________________________
In sickle cell disease, the sequence of amino acids
is different in just one spot. The sequence above
becomes: proline, valine, glutamic acid, lysine.
11. Translate the sickle cell amino acid sequence
into:
a. tRNA base code ____________________
Now can you do it the other way around?
amino acids
Part E: Base Sequence Errors and Mutations
tRNA code
(codon)
proline
glutamic acid
lysine
serine
leucine
mRNA code
(anticodon)
b. mRNA base code _______________________
DNA code
c. DNA base code ______________________
12. In terms of base nucleotides, explain the only
difference between the DNA code for
normal hemoglobin and sickle cell disease.
Analysis Questions:
1. a. What is the structure and function of mRNA? ____________________________________________________
_______________________________________________________________________________________
b. Why is messenger RNA a good name? _________________________________________________________
________________________________________________________________________________________
2. What happens during transcription? _______________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
3. a. What is the structure and function of tRNA? _____________________________________________________
________________________________________________________________________________________
b. Why is transfer RNA a good name? ____________________________________________________________
________________________________________________________________________________________
4. What happens during translation? ________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
5. What does this mean?
DNA
RNA
PROTEINS
On this table, compare DNA, mRNA and tRNA by checking all that apply:
DNA
Contains deoxyribose
Contains ribose
Contains a phosphate group
Contains adenine
Contains thymine
Contains uracil
Contains cytosine
Nucleotides
Carries a chemical message or code
Stays only in the nucleus
Carries the message out of the nucleus into the cytoplasm
Always in the cytoplasm
Is a double strand
Is a single strand
Carries an amino acid to a ribosome
mRNA
tRNA