Archive of ‘Grade 12’ category

10
May
2022

Oral Storytelling

categories: English 12

Brief Introduction

Today in English Studies 12, we talked a lot about oral storytelling. We spoke about its value  and how it was questioned in the past. Hearing my own classmates stories and sharing my own has fostered a deeper connection with the class and the students in it. Before leaving today, we were told to write a reflection either on what we learnt or what this lesson made us think about.

The Reflection

Learning about oral storytelling has helped me understand its value and how it was disregarded in the past. I had not realized how little value people placed on these kinds of stories. Though I do understand the worry over the possibility of changes as the story is retold and passed down, is it not true that the message would remain the same? The story has a purpose and that would not change due to a few minor differences. Additionally, learning about oral storytelling has helped me place more value on the oral stories my own family has told me. My grandfather often reminisces about his past and the things he has gone through. Much of my family writes these stories off as the ramblings of an old man. However, now I see the value in the passing of these life lessons and understand that his stories have a purpose. For example, the stories my grandfather has of his school days and how he was not a good student. He does not tell them just to be funny and laugh at the idiocy; he means to share how he placed little value on education in his youth and that my cousins and I should work hard and value education.

A Picture: My grandparents and some of my cousins

19
Oct
2021

A&P – DNA and Protein Synthesis

categories: Grade 12

Brief Introduction

In Anatomy and Physiology 12, we did numerous modeling activities about how DNA replicates and how proteins are made. We talked about the differences between DNA and RNA and how those differences affected their roles. This blog post is an overview of what I took away from those activities.

Questions, Answers and Pictures

DNA Replication

  1. Explain the structure of DNA – use terms nucleotides, antiparallel strands, and complimentary base parings.

DNA is a double helix shape (like a twisted ladder). The “rungs” of said ladder are made up of nucleotides. The four nucleotides are Guanine, Cytosine, Adenine and Thymine. Due to their structures, each nucleotide has a specific bonding partner. Adenine and Thymine form double bonds with one another, while Guanine and Cytosine form three bonds. The side parts of the ladder are anti-parallel, meaning that they are going in contrasting ways. For example, like a two cars on a highway driving in separate directions.

  1. When does DNA replication occur?

DNA replication occurs prior to cell division.

  1. Name and describe the three steps involved in DNA replication. Why does the process occur differently on the leading “leading” and “lagging” strands?

There are three steps in DNA replication. The first step is unwinding and unzipping, which is exactly what it sounds like. The DNA is unwound and unzipped by an enzyme called DNA Helicase (it unzips the DNA by breaking the hydrogen bonds between bases).

After DNA helicase breaks these bonds, complementary base pairing is the next step. This step uses DNA Polymerase to create the complementary base pairings (Adenine to Thymine and Guanine to Cytosine). As the DNA polymerase makes it down the unzipped strand of DNA, it gets the new complementary bases from a pool of free-floating nucleotides.

The final step is joining. This step is done by new enzymes in two different places. Firstly, DNA polymerase forms sugar-phosphate covalent bonds between adjacent nucleotides. The DNA will then form its helix shape. On the lagging strand, it is a bit more complicated. Since the DNA strands are anti-parallel to one another, the DNA polymerase can only read one strand continuously (known as the leading strand). The other strand ends up with gaps where bonds should have formed but didn’t due to DNA polymerase needing to read “backwards”. These unbonded fragments are then bonded together by DNA ligase.

  1. Today’s modeling activity was intended to show the steps involved in DNA replication. What did you do to model the complimentary base parring and joining of adjacent nucleotides steps? In which ways was this activity well suited to showing this process? In what ways was it inaccurate?

During our modeling activity, we went through the steps of DNA replication. Our model consisted of green pentagons (deoxyribose sugar), teal circles (phosphate), beige hexagons (Cytosine), yellow hexagons (Thymine), baby blue polygons (Adenine) and robin’s egg polygons (Guanine). To model complimentary base paring and the adjoining of adjacent nucleotides, we did a number of things. We started off with showing how the DNA is cut by DNA helicase and how DNA polymerase’s job was to match the bases. For the adjoining of adjacent nucleotides, we showed how on the lagging strand, DNA ligase would join them together.This activity was well suited to show the process because it allowed us to represent each step and learn how the transition between steps worked. It also gave us the chance to familiarize ourselves with the shapes of purines vs pyrimidines and how the bonds worked (triple bonds between Cytosine and Guanine). Due to the size of our model, we could observe how the enzymes did their jobs and how they interacted with the original parent strand. The different shapes used for the enzymes were also helpful in learning how to distinguish which does what job. Though overall this was a good activity, there were some inaccuracies with our model. Firstly, since we were limited to 2D, we weren’t able to “unwind” our model. Also, due to the sheer complexity of this process, how we modeled the enzymes were oversimplified. In reality, the structure of all these enzymes is much more complex than the simple shapes used to represent them. Although, those shapes were good for showing the function of the enzymes (ex. how helicase was scissors).

 

RNA Transcription

  1. How is mRNA different than DNA?

mRNA and DNA differ in many ways. Firstly, the base they use to pair with Adenine are different. mRNA uses Uracil while DNA uses Thymine. They also differ in size: mRNA is much smaller (~1000 nucleotides in length) and it is able to leave the nucleus while DNA is too large to leave the nucleus. Additionally, mRNA is single stranded and therefore its structure is much simpler when compared to DNA’s double-stranded twisted-ladder structure. The sugar in mRNA (ribose) is different than that in DNA (deoxyribose). Lastly, the information they contain is different. DNA contains all of the genetic information and mRNA contains the “instructions” for just one gene.

  1. Describe the process of transcription

The process of transcription is a rather short one.

To begin, a segment of DNA is unzipped and unwound to allow for the formation of mRNA. This segment of DNA contains the gene that the mRNA is going to transcribe.

RNA polymerase is now responsible to make the complementary strand to the DNA. The bases used are Adenine, Uracil, Cytosine and Guanine.

After this complementary strand is built, it is detached from the DNA and is able to leave the nucleus due to its small size.

The DNA then reattaches and is left unaltered and unchanged. Whereas the mRNA now holds the instructions to create one protein.

  1. How did today’s activity do a good job of modeling the process of RNA transcription? In what ways was our model inaccurate?

Today’s activity did a great job of showing how the DNA is left unchanged and how the sugars in RNA and DNA are different. The model was inaccurate in a few ways as well. Once again, we were limited to 2D and were unable to model the process of unwinding. There are also some steps missing, such as where did the RNA come from and how the where the mRNA would go afterwards. Finally, in our models the mRNA and DNA were similar sizes which left some questions as to how the mRNA would be able to leave the nucleus and the DNA wouldn’t.

 

Protein Synthesis

  1. Discuss the process of translation: initiation, elongation, and termination

Initiation is the first step. During this step, the mRNA bonds to the small sub-unit of ribosomes and then the two subunits join together.

The next step is elongation. This is when the ribosome reads the first codon (“Start” codon) on the mRNA and then calls the tRNA with the corresponding anti-codon and amino acid. The tRNA with the first amino acid will arrive at the P slot.

The ribosome then moves onto the next codon and calls the tRNA with its corresponding anti-codon and amino acid to the A slot.

When both slots are filled, the amino acid on the P slot will be transferred to the tRNA attached to the A slot.

Once the transfer is complete, nothing is holding the tRNA at the P slot there, so it goes away and the tRNA at the A slot is moved to the P slot. This process then repeats, until the last step, termination.

Termination happens when the ribosome reads the “stop” codon. This codon doesn’t correspond to any of the 20 amino acids, so nothing is added to the chain. The polypeptide then disconnects from the ribosome, ending the process of translation.

  1. How did today’s activity do a good job of modeling the process of translation? In what ways was our model inaccurate?

Today’s activity did a good job of modeling the process because it gave us a chance to learn about the codons and their corresponding anti-codons. We learnt how to “read” the three letter codons and how to find out what their anti-codons were. During this process, we also got to see how the amino acids were stacked. Since our time was limited, there were some steps that were skipped, losing some accuracy in our model (ex. how we didn’t model every amino acid arriving and then being transferred). The shapes of the things in our model (ex. the amino acids) were also simplified.