Download tRNA and Translation

tRNA AND TRANSLATION
OBJECTIVES
1. What is the structure and function of transfer RNA? (MCA-II science standard)
2. How does translation work? (MCA-II science standard)
3. What is evolution? (MCA-II science standard)
INTRODUCTION
DNA, the molecule which provides the blueprint for life, is located in the nucleus of cells.
mRNA, which formed in the nucleus from DNA, will leave the nucleus, move out to special cell
structures called ribosomes, and direct the building of proteins. The building of proteins will
involve another type of RNA as well, called transfer RNA or tRNA.
PROCEDURE
Part A
tRNA is similar in structure to mRNA but with one key difference.
1. What is the name of the sugar in the mRNA nucleotide? __________________________
2. Look at the green models of tRNA nucleotides found in your packet.
What is the name of the sugar in the tRNA nucleotide?
_______________________
Note that tRNA and mRNA have the same sugar.
3. What is the name of the acid in the mRNA nucleotide? __________________________
4. Look at the green models of tRNA nucleotides found in your packet.
What is the name of the acid in the tRNA nucleotide?
_______________________
Note that tRNA and mRNA have the same acid.
5. What are the four nitrogenous bases found in mRNA?
a. __________________________
b. __________________________
c. __________________________
d. __________________________
6. Look at the green models of tRNA nucleotides found in your packet.
What are the four nitrogenous bases found in tRNA?
a. __________________________
b. __________________________
c. __________________________
d. __________________________
Note that tRNA and mRNA have the same nitrogenous bases.
7. mRNA is built as a single-stranded molecule.
√ In comparison, how would you describe the structure of tRNA?
_______________________________________________________________________
Part B
In this section of the lab, you will model the process of translation.
1. We will start by assuming that mRNA has already formed from DNA by transcription.
2. Build a model of a single-stranded mRNA molecule according to the table below.
3. What tRNA nucleotides will match to the single-stranded mRNA molecule?
Complete the table below.
mRNA nucleotides
tRNA nucleotides
guanine
adenine
cytosine
uracil
cytosine
guanine
4. Using the table you completed as a guide, match the green tRNA nucleotide models to
the yellow mRNA nucleotide models. This process occurs outside the nucleus at
specialized structures called ribosomes.
5. The tRNA molecules are called transfer RNA because they transfer specific molecules
of amino acid. The amino acids will be used to create protein. Match the two green
amino acid molecule models to the tRNA molecule models.
Which amino acid matches the cytosine / guanine / adenine tRNA? _________________
Which amino acid matches the guanine / uracil / cytosine tRNA?
_________________
6. You have now formed a small protein model composed of two amino acids.
Show your model to your teacher and have him/her sign off. ____________________
Part C
The process of translation is a matter of translating the message of a series of
molecules including DNA, mRNA, and tRNA. A specific sequence of amino acids,
or a protein, is formed as a result of the process of translation.
1. mRNA is linked to DNA in the process of ___________________________.
Complete the mRNA column of the table.
2. tRNA is linked to mRNA in the process of ___________________________.
Complete the tRNA column of the table.
3. tRNA transfers specific amino acids to form a protein. Use the “tRNA nucleotides /
amino acids” table to learn how specific amino acids and tRNA molecules link.
Complete the amino acid column of the table.
4. The first row of the table has been completed for you as an example.
DNA nucleotides
mRNA nucleotides
tRNA nucleotides
AAT
UUA
AAU
amino acids
leucine
GGG
ATA
AAA
GTT
tRNA nucleotides amino acid
AGC
serine
GGG
proline
AAU
leucine
CUU
glutamic acid
AUA
tyrosine
GCU
arginine
AAA
phenylalanine
CAA
valine
UUU
lysine
GUU
glutamine
Part D
Not often are there errors in the process of forming proteins from the DNA code of
instructions. An error in the process of forming a protein is called a mutation. In an
effort to help you understand how errors can occur, we will be looking at a blood
protein called hemoglobin.
1. Normally the message of DNA, mRNA, tRNA, and amino acids is translated correctly.
In this way, the hemoglobin protein efficiently carries oxygen to cells. Complete the
table below that summarizes the normal translation of the message.
DNA nucleotides
GGG
CTT
CTT
TTT
mRNA nucleotides
tRNA nucleotides
amino acids
2. Sometimes the sequence of DNA nucleotides is not formed correctly. In some people, a
very particular disarrangement of DNA nucleotides results in a disease called sickle-cell
anemia. Their red blood cells are sickle-shaped rather than round. As a result, their red
blood cells cannot transport oxygen as well, resulting in a painful debilitating disease.
Note the difference that a slight change in DNA nucleotides can make.
DNA nucleotides
mRNA nucleotides
tRNA nucleotides
amino acids
GGG
CAA
CTT
TTT
3. The proper arrangement of almost 600 amino acids results in normal formation of the
hemoglobin molecule. According to the question above, one mistake involving the
replacement of the amino acid ______________________________________ by the
amino acid ____________________________________ can result in sickle-cell anemia.
4. Question Sickle cell anemia is the most common genetic disorder among African
Americans. This disease can damage the heart and brain and in some cases may be fatal.
Then why does this disease persist among African Americans?
Answer The answer comes in the fact that many African Americans are only carriers
of the disease, meaning that they carry the trait but do not actually have the disease.
Carriers are healthy and, in addition, are resistant to another disease called malaria.
Application Suppose that a mutation occurs in the DNA of a desert lizard.
Because the DNA changed, then the __________ changed.
(Hint: this molecule is formed by transcription)
Because the mRNA changed, then the sequence of __________ __________ changed.
(Hint: these molecules are transferred by tRNA)
Because the sequence of amino acids changed, the __________________ changed.
(Hint: this molecule is formed by translation)
Now suppose that the pigment in the lizard tail is made of protein. Because of the
mutation, the protein and thus the pigment changed to blue. How will a blue-tailed
lizard fair in a desert of brown soil?
______________________________________
How will the ratio of blue to brown-tailed lizards likely change?
_________________
Change in an organism over time, such as lizard tail color, is called evolution.