mRNA AND TRANSCRIPTION
OBJECTIVES
1. What is the structure and function of messenger RNA? (MCA-II science standard)
2. How does transcription work? (MCA-II science standard)
INTRODUCTION
DNA, the molecule which provides the blueprint for life, is located in the nucleus of cells.
Another molecule, called messenger RNA or messenger ribonucleic acid or mRNA, is formed in
the nucleus as well. mRNA directs the formation of protein.
PROCEDURE
Part A
1.
mRNA is similar in structure to DNA but with some key differences.
What is the name of the sugar in the DNA nucleotide? __________________________
2. Look at the yellow models of mRNA nucleotides found in your packet.
What is the name of the sugar in the mRNA nucleotide?
_______________________
√ The type of sugar is one of the three key differences between mRNA and DNA.
3. What is the name of the acid found in the DNA nucleotide? _______________________
4. Look at the yellow models of mRNA nucleotides found in your packet.
What is the name of the acid in the mRNA nucleotide?
_______________________
Note that DNA and mRNA have the same acid.
5. Nitrogenous bases form the rungs of the DNA spiral ladder. Why are they said to be
nitrogenous? ___________________________________________________________
6. What are the four nitrogenous bases found in DNA?
a. __________________________
b. __________________________
c. __________________________
d. __________________________
7. Look at the yellow models of mRNA nucleotides found in your packet.
What are the four nitrogenous bases found in mRNA?
a. __________________________
b. __________________________
c. __________________________
d. __________________________
8. What is the new nitrogenous base found in mRNA? _____________________________
√ The nitrogenous bases are one of the key differences between mRNA and DNA.
9. DNA nitrogenous bases pair in a particular pattern. How do the bases pair?
______________ with ______________ and ______________ with ______________
10. mRNA nitrogenous bases pair in a particular pattern but slightly different than DNA.
Remember that mRNA has the nitrogenous base uracil instead of thymine. How do you
suppose that the mRNA nitrogenous bases pair?
______________ with ______________ and ______________ with ______________
11. DNA nucleotides form a sort of twisted ladder that Watson and Crick called a double
___________________. In contrast, mRNA forms just a single-stranded molecule.
√ The double versus single strand is one of the differences between DNA and mRNA.
Part B
In the process of transcription, mRNA is formed from DNA.
The mRNA molecule will go on to direct the production of protein.
1. How do DNA nucleotides match to form a double helix?
Complete the table below, at left.
2. Build a DNA model according to the table you completed.
3. Open your DNA model along the point of attachment between nitrogenous base pairs.
In so doing, you will create two matching columns of DNA nucleotides.
4. How do mRNA nucleotides match DNA to form a single strand?
Complete the table below, at right.
5. Using the left hand side of the DNA model as a pattern, build the mRNA single strand.
6. Remove the mRNA single strand from the left hand column of DNA.
7. Put the two columns of DNA back together to form the original DNA model.
8. You should now have a double helix DNA model and a single strand mRNA model.
Show your two models to your teacher and have him/her sign off. _________________
DNA nucleotide
DNA nucleotide
DNA nucleotide
cytosine
cytosine
thymine
thymine
guanine
guanine
adenine
adenine
guanine
guanine
cytosine
cytosine
mRNA nucleotide