Names of Group Members:
In this activity you will construct the gene for insulin, replicate it via DNA
synthesis, and then build the insulin polypeptide via protein synthesis and posttranslational modifications. Each group should consist of five members. For each
group, you will assign a group leader to read the instructions, assign jobs, and
make sure everyone is doing their job correctly.
Group #:
Cytosol
The coding region of the insulin gene is 330 nucleotides long. This is the region
responsible for the actual amino acid sequence. In addition to the coding region,
genes contain regulatory regions involved in turning the gene on and off, and
needed for signaling the start and end of the genes. Non-coding regions are also
involved in directing post-translational modifications to the protein.
ER
Lumen
The insulin gene actually codes for preproinsulin, a polypeptide that consists of
110 amino acids. However, preproinsulin is converted to insulin during post
transcriptional modifications that include removing two segments of the protein
(the D chain and the C chain), leaving behind the A chain and the B chain, which
are held together via two disulfide bonds.
Golgi
Secretory
Vesicle
Part 1 Constructing Your Template DNA
Work together to cut out the nucleotides and tape them together to form the insulin gene. Use the sequence analysis paper showing
the mRNA sequence for insulin and the corresponding sequence of amino acids as your guide. Things to consider:
 You have been given the mRNA sequence, which you need to convert into the DNA sequence.
 Your DNA should be double-stranded and composed of two complementary strands not two identical strands.
 Tape covalently bonded nucleotides directly to one another (DNA backbone) but leave a small space of clear tape between
hydrogen-bonded nucleotides (between two nitrogenous bases) to indicate H-bonds.
 When the oxygen of a phosphate covalently bonds to deoxyribose, a hydroxyl group (OH) from the deoxyribose combines with
a hydrogen ion and is lost as water (H2O).
 The 3’ end has a free deoxyribose and the 5’ end has a free phosphate.
Part 2 Replicating Your DNA
In DNA replication, the double helix is unwound, the hydrogen bonds are broken, and each complementary strand is used as a
template to build a new double-stranded DNA dimer. DNA synthesis is said to be semi-conservative because each resulting DNA
dimer is composed of a strand of the original DNA (conserved) and a complementary new strand of DNA (just synthesized). Assign
one group member to play each role below.
Team Leader: read the directions and make sure the daughter strands are correctly synthesized.
_________________________
Name
Topoisomerase: unwinds the DNA double helix ahead of the replication fork.
Helicase: breaks the hydrogen bonds between complementary bases ahead of the
replication fork (use scissors - try to keep about 10 bases ahead of the
replication fork and only break the next H-bond after each nucleotide
is added to each new strand being synthesized).
Primase: specialized RNA polymerase that builds a five nucleotide-long segment of
RNA (primer) at the start of the leading strand and after every 100 nucleotides
of the lagging strand.
DNA polymerase: reads a strand in the 3’ to 5’ direction matching complementary
bases to it and covalently bonding them together to build a complementary
strand in the 5’ to 3’ direction. The DNA polymerase on the leading strand
replicates continuously, while the DNA polymerase on the lagging strand
releases the DNA at the end of each Okazaki fragment and reconnects at the
end of the next primer (where the next Okazaki fragment will start).
RNase H: digests the RNA primer after its been used by DNA polymerase to get started
DNA polymerase: fills in DNA nucleotides where the RNA nucleotides were
DNA Ligase: seals holes in the DNA backbone left by removal of the RNA primers by
forming a covalent bond between the unconnected deoxyriboses and phosphates
_________________________
Name
You need two DNA polymerases, one for
the leading strand and one for the
lagging strand:
_______________________________
Name
_________________________
Name
_________________________
Name
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