Lab 7: Transcription and Translation
• To build a DNA molecule
• To simulate DNA replication
• To simulate transcription by building an mRNA molecule from DNA
• To simulate translation by building a polypeptide chain from the mRNA transcript
• Pen and paper or computer.
Description of the problem
You will build a DNA and RNA molecule and simulate the processes of DNA replication, transcription, and translation. You may find it helpful to refer to the figures in Ch. 22 from your book.
Building a DNA molecule
DNA is composed of monomers of nucleotides. Each nucleotide contains a 5-carbon sugar (=
deoxyribose), a phosphate, and a nitrogenous base (adenine, cytosine, guanine, or thymine).
Since DNA is a double-stranded molecule, adenine (A) on one strand always pairs with thymine
(T) on the other strand, whereas cytosine (C) always pairs with guanine (G).
- What molecules make up the backbone of DNA? What four molecules make up the “rungs” of the DNA “ladder” (be specific)? Build a DNA molecule that is 6 base pairs long by choosing 6 bases for one strand and the complementary bases for the second strand.
- For the molecule you just built, write the sequence of bases (A, C, G, T) you used on one strand and the complementary bases on the other strand.
Simulating DNA replication
DNA undergoes semi-conservative replication.
Before this begins, DNA must first “unzip” (the
picture at right is a simulation of this occurring).
- What bonds are broken in order to unzip the DNA?
Unzip your DNA molecule. Attach new complementary nucleotides to each strand using
complementary base pairing.
- What is meant by semi-conservative replication?
Like DNA, RNA is composed of monomers of nucleotides. Each nucleotide contains a 5-carbon
sugar (= ribose), a phosphate, and a nitrogenous base. Unlike DNA, RNA is a single-stranded
- What are the 4 bases in RNA? DNA serves as a template to make mRNA. Adenine (A)
in DNA always pairs with what base in mRNA?
One strand of DNA serves as the template to make mRNA in the process known as transcription.
Transcription is the first step in expressing a gene.
- Extend your original DNA molecule by making it 12 (instead of 6) base pairs long. What
is the base sequence of your two DNA strands (they should be complementary with one
- Choose one strand of DNA from #6 to serve as the template to make mRNA. What is the
sequence of bases in your mRNA transcript?
Once mRNA is made, it will eventually leave the nucleus and go to the ribosomes in the
A sequence of three bases in mRNA codes for a particular amino acid. The process of
converting the sequence of bases in RNA into a sequence of amino acids in a protein is called
translation. Translation occurs on the ribosomes in the cytoplasm of the cell.
- What is the name of each three-base sequence in mRNA?
In cells, tRNA with an anticodon complementary to the codon in mRNA will transport its
attached amino acid to the ribosome. The next mRNA codon is “read” by the ribosome, whereby
another tRNA with the correct anticodon and its associated amino acid will attach. The two
amino acids are joined together with a peptide bond. This process is repeated until the last codon
in the mRNA is read. The end result will be a polypeptide chain composed of many amino acids.
- Using the mRNA transcript you generated in #7, what are the first three amino acids of
your polypeptide chain? (See Fig. 22.6 in your book.)
- What happens to the mRNA transcript after translation is complete?
ALL QUESTIONS IN THE BOXES MUST BE ANSWERED. Please include the questions
with your responses and upload the assignment to the appropriate assignment submission folder.