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Henry Hodaly
Biology 12, Block D
April 29, 2017
DNA and Protein Synthesis
DNA Model
1. Explain the structure of DNA – use the terms nucleotides, antiparallel strands, and
complimentary base pairing.
Deoxyribonucleic Acid (DNA), is a large molecule that controls cells activities and has the
instructions on how to build proteins. The monomers of nucleic acids are nucleotides, and
a single DNA molecule contains approximately 85 million nucleotides. The nucleotides of
DNA are composed of a deoxyribose sugar bonded to a phosphate group as well as a
nitrogenous base. For DNA, there are two purine bases and two pyramidines bases. The
purines bases are adenine and guanine, while the pyramidines are cytosine and thymine.
The structure of DNA can be described as two sugar phosphate backbones twisted in to an
antiparallel double helix. The bonds between the sugar and the phosphate are covalent. The
strands run antiparallel to each other, which means that one strand has a phosphate pointing
up while the other has a phosphate pointing down. Complimentary base pairing is when
hydrogen bonds form between the nitrogenous bases on the two strands. Adenine will only
bond with thymine, while guanine will only bond with cytosine.
2. How does this activity help model the structure of DNA? What changes could we
make to improve the accuracy of this model?
This activity allows students to develop a basic understanding of the structure of DNA
using simple materials. Some aspects of this lab that were helpful in expressing that
structure of DNA was showing how the antiparallel strands were built using the beige beads
and how the purines had two beads on them to show the difference in their nitrogenous
bases. Something we could have done to improve the lab could be using additional
materials to show the hydrogen bonding between the nitrogenous bases and making it
larger, since DNA is a huge molecule. These two pictures represent DNA when it is flat in
its ladder form and when it is twisted in to a double helix.
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Henry Hodaly
Biology 12, Block D
April 29, 2017
DNA Replication Model
1. When does DNA replication occur?
DNA replication is when a DNA strand duplicates itself. This process always occurs prior
to cell division.
2. Name and describe the 3 steps involved in DNA replication. Why does the process
occur differently on the “leading” and “lagging” strands?
The three stages involved in DNA replication are unwinding and unzipping,
complimentary base pairing, and the joining of adjacent nucleotides.
Unwinding and Unzipping- In this first step, DNA helicase breaks down the hydrogen
bonds between the complimentary base pairs starting from the top of the chain.
Complimentary Base Pairing- DNA polymerase now moves through the leading and
lagging strands and pairs new nucleotides with the template strands. This process occurs
differently on the two strands because DNA polymerase can only read from 3’ to 5’, which
means that is reads the sugar and then the phosphate. So the DNA polymerase starts at
opposite ends of each strand since DNA is antiparallel.
Joining of Adjacent Nucleotides- In the final step, DNA ligase moves through the strands
and creates bonds between the sugar and the phosphate, completing the molecule.
This picture represents the first step of DNA
replication, unzipping and unwinding. The DNA helicase is breaking the bonds between
the nucleotides.
3. The model today wasn’t a great fit for the process we were exploring. What did you
do to model the complimentary base pairing and joining of adjacent nucleotides steps
of DNA replication?
For these two steps, we found it inefficient to bond the nucleotides together before bonding
the sugar-phosphates to create a new strand based on the materials we had. Instead, we
attached the nucleotides to the new DNA strands before bonding them to their adjacent
nucleotides. This isn’t how the process occurs in reality, but it was much easier to do it
this way for the activity with the materials we had.
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Henry Hodaly
Biology 12, Block D
April 29, 2017
RNA Transcription Model
1. How is mRNA different from DNA?
DNA and mRNA are different in many ways. DNA has two sugar phosphate backbones
while mRNA only has one. Also, a DNA molecule is over 85 million nucleotides long,
while an mRNA molecule is approximately 1000. Finally, the nitrogenous bases of DNA
are adenine, guanine, cytosine, and thymine, while the bases of mRNA are adenine,
guanine, cytosine and uracil.
2. Describe the process of transcription?
The process of transcription can be broken down in to 3 phases, unwinding and unzipping
of DNA, complimentary base pairing with DNA, and separation from DNA. The first step
is when DNA helicase breaks down the hydrogen bonds between the nucleotides.
The next step is when RNA polymerase reads the bases on the sense strand, as this strand
contains the correct information on how to build proteins. The other nonsense strand if
copied will not create a protein as its information is gibberish.
The final step is when the mRNA strand will detach itself from the sense strand of the
DNA. The two strands of DNA will then join together again. Immediately after
transcription is complete, the mRNA will still have to be modified before it can be sent
out of the nucleus to deliver its message. This picture has s small error in it as it shows the
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Henry Hodaly
DNA
Biology 12, Block D
strands
bonding
again
before
the
April 29, 2017
mRNA
strand
has
detached.
3. How did today’s activity do a good job of modelling the process of RNA
transcription? In what way was our model inaccurate?
Today’s activity accurately modeled RNA transcription because we showed how the RNA
polymerase only reads on the sense strand of the DNA gene. It was also good because we
were able to use different coloured beads to show how RNA has a different base than
DNA. Our model was inaccurate by the fact that a real RNA molecule is approximately
1000 nucleotides long while our model was only 18. Also, when our RNA was copied
from the DNA, you could see the phosphate first, when you shouldn’t have.
RNA Translation Model
1. Describe the process of translation: initiation, elongation, and termination?
Translation is when ribosomes read mRNA’s message and strings together the
corresponding amino acids to make the required protein. In the first step of initiation, the
mRNA molecule is held by the ribosome and the start codon is read by the P-site, with the
anticodon then matched to it. The correct amino acid is then brought by the tRNA and
attached to the anticodon.
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Henry Hodaly
Biology 12, Block D
April 29, 2017
The next step, elongation, is when the amino acid chain continues to grow. The following
codons are then read, matched with their anticodon, and then the tRNA brings in the
appropriate amino acid. After a codon is read, it moves off the P-site and the amino acid
of this P-site then moves to the top of the A-site.
Finally, termination is when the next mRNA codon is a stop codon, and there is no
matching tRNA for a stop codon. The ribosome then lets go of the mRNA and the tRNA
releases the polypeptide.
2. How did today’s activity do a good job of modelling the process of RNA translation?
In what way was our model inaccurate?
Our model properly illustrates the process of translation because we were able to show
how this process was initiated and the pairing of the codons with their corresponding
amino acids. Our model was inaccurate by the fact that we never actually reached an end
codon but we were forced to stop anyway. This is because our model was not long enough,
when in reality, the mRNA is approximately 1000 nucleotides in length.
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