- Explain the structure of DNA – use the terms nucleotides, antiparallel strands, and complimentary base pairing.
The structure of a DNA is a long polymer that is made out of many nucleotide monomers. It has two backbones that have a sugar and phosphate bonded pattern. The two backbones are not identical, as the sugar phosphate bond are opposite form each other, also known as antiparallel strands (1-phosphate-sugar-phosphate 2-sugar-phosphate-sugar). Furthermore, the bases are always paired with the same partner (purine-pyrimidine) à Adenine & Thymine; Guanine & Cytosine.
- How does this activity help model the structure of DNA? What changes could we make to improve the accuracy of this model? Be detailed and constructive.
This model helps show the structure of the DNA through the colored bases, that helps recognize their partnered base. Also, it shows the sugar phosphate antiparallel strands, as shown through the black beads. In addition, the twist in the DNA stricture is easily achieved by the bending capability of the pipe cleaners. The model could be improved if the bonds in the middle were shorter, thus to making the twist look a little messy. When we bent the DNA structure the long bonds would not stay straight thus twisting and bending as well, which is not how the DNA structure should look.
3. When does DNA replication occur?
It occurs before cell division.
4. Name and describe the 3 steps involved in DNA replication. Why does the process occur differently on the “leading” and “lagging” strands?
-Unwinding & unzipping- DNA helix-case – Complimentary base pairing- DNA polymeras – Joining of adjacent nucleotide- DNA ligase
The process occurs differently for the leading and lagging strands because they are built differently. The leading strand is built from the 3’ end to the 5’ end, which is the strand that has the sugar at the top of the strand. However, the lagging strand is built oppositely with 5’ at top and 3’ at bottom. DNA polymerase works in small segments, reading the strand backwards. ** DNA polymerase is responsible for H-bonding new nucleotides to the strand, it can only read DNA in one direction. From 3’ end to 5’ end.**
5. 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. In what ways was this activity well suited to showing this process? In what ways was it inaccurate?
We attached the (little white pipe cleaner) nucleotides to half of the parent DNA (backbone with unpaired nucleotides) to form a daughter DNA. For the leading strand we had to attach from top (3’) to bottom (5’). Though for the lagging we had to build backwards form bottom to top.
It was inaccurate because technically the DNA backbone is not one long strand of sugar phosphates (represented by blue pipe cleaner). It is supposed to be phosphates and sugars bonded together molecule by molecule as each nucleotide is paired. Furthermore, due to the fact that we created the model by hand, it is impossible to accurately replicate the parent DNA, since in reality they are exact copies of one another. For example, the length of our nucleotides and the length of their hydrogen bonds were not all the same which created a relatively uneven model. However, it was accurate because it gave us a good visual to show the same sequence DNA that was split to form same sequence daughter DNA. It also, gave a good visual to show the attachment of the lagging and leading strands.
6. How is mRNA different than DNA?
The difference between mRNA and DNA is that m RNA has 1 backbone, while DNA has 2 backbones. Additionally, mRNA is built with RNA polymerase (superhero), while DNA is built with DNA polymerase & DNA Ligase. Furthermore, mRNA carries DNA’s message and information, while DNA doesn’t carry any RNA information or messages.
7. Describe the process of transcription.
Transcription starts with the RNA polymerase who binds to a sequence of DNA called the promoter. Which is found near the beginning of a gene. It then separates the two strands of DNA apart. Then, one DNA strand acts as a template for RNA polymerase. As it reads the template it creates an RNA molecule out of complimentary nucleotides. The RNA molecule that is created holds the same information as the non-template DNA though, instead of Thymine it uses Uracil. Finally, sequences called terminators signal that the RNA is complete. Once it is complete, it is released form the DNA polymerase.
8. How did today’s activity do a good job of modelling the process of RNA transcription? In what ways was our model inaccurate?
It was a good way of modelling the process of RNA transcription because it showed how the RNA molecule that is created matches the ‘non-template’ DNA strand. It also shows very well how the Thymine is changed to Uracil on the RNA molecule. In addition, it shows how the DNA Splits apart by RNA polymerase and then rejoins back together very well also. Finally, due to the fact that it was easily moveable it was very simple to show how the DNA ‘unwinds’ before it gets separated.
The model was inaccurate because it was difficult to truly show how it creates its complimentary bases.
9. Describe the process of translation: initiation, elongation and termination.
Is when the code that is carried by mRNA is transformed into a polypeptide. First step is initiation, which is when mRNA binds to the small ribosome subunit. The two ribosome subunits then bind together, reads the start codon. The second step is elongation, which is when ribosome moves along mRNA reading each codon, bringing in the complimentary tRNA and building amino acid chain. Finally the third step is termination, which is when a ribosome reads a stop codon, no complimentary tRNA for a stop codon. This makes the ribosome release mRNA, tRNA and polypeptide strand.
10. How did today’s activity do a good job of modelling the process of translation? In what ways was our model inaccurate?
This model was accurate because it showed how the ribosomes move along and the process of elongation. However, it was inaccurate because we were ‘moving’ the tRNA while the mRNA should have been the one ‘moving’. (was away for the beginning of lab due to arm therefore it made it more difficult to understand the model).
