Protein synthesis is divided into two stages: Translation and Transcription
Down below I will be explaining these processes in more detail.
Differences between mRNA and DNA
mRNA:
- Created during the process of Transcription
- Role is to determine the order of amino acids for a Protein
- Known as the “messenger” RNA
- Contains the sugar Ribose
- Made up of the bases Adenine, Guanine, Uracil and Cytosine
- Does not have a double helix shape
DNA:
- Stores the information for the genes in living organisms
- Constantly making new copies of itself to form new DNA strands
- Contains the sugar Deoxyribose
- Made up of the bases Adenine, Guanine, Cytosine and Thymine
- Created during the DNA replication process
- Located inside the nucleus
- Has a double helix shape
PROCESS OF TRANSCRIPTION: Converting DNA to mRNA
3 stages of Transcription:
- Unwinding/Unzipping of DNA double helix
- Complimentary Base pairing
- Separation of DNA
- Unwinding/Unzipping of DNA double helix
A visual model of a DNA double helix structure is shown in the image below.
The beige hexagon represents Cytosine. Thymine is represented by the yellow hexagon, Guanine by the darker blue polygon, and Adenine by the lighter blue polygon. Every base is linked to a phosphate group (represented by the teal circle) and a deoxyribose sugar (the green Pentagon)
DNA double helix structure
The dotted lines represent the formation of hydrogen bonds between the base partners (Adenine pairs with Thymine and Cytosine pairs with Guanine)
Transcription occurs in the nucleus and is activated by RNA polymerase. RNA polymerase is an important enzyme that creates a sequence of nucleotides that will be later used to make mRNA (messenger DNA)
The process of Transcription starts when RNA polymerase attaches to the DNA strand and unwinds the double helix structure to form two separate strands of DNA.
Unwinding of the Double Helix
Because nucleotides can only be added from the “5 to 3” direction RNA polymerase will only add nucleotides along one strand because the other strand is anti-parallel and read in the opposite direction.
The strand that RNA polymerase is adding nucleotides too is named the template strand (or the Nonsense strand) because it will be used as a template for complimentary base pairing to form mRNA. The other side of the DNA molecule is known as the “Sense Strand” because its bases are complimentary to the Nonsense strand and the mRNA strand that will be created.
2. Complimentary base pairing
The picture below on the left side represents the complimentary base pairs that occurs to create an mRNA molecule.
RNA polymerase is represented as the yellow heart.
The picture on the right also represents the process of Complimentary base on the mRNA strand.
RNA Complimentary base pairing
RNA Polymerase is going to form hydrogen bonds between the base partners on the template strand and connect the nucleotides together to form the backbone of the RNA molecule.
Guanine will still pair with Cytosine, but Adenine will pair with Uracil instead of Thymine. The light green polygon represents Uracil.
In the diagram above, each base is bonded to their partner, a phosphate group, and a ribose sugar group (bright red circle), rather than Deoxyribose, as we previously saw in the DNA double helix molecule structure.
Separation of DNA:
Because DNA is unaffected by transcription, it reforms, and RNA undergoes changes before converting to mRNA and then it transfers to the cytoplasm to begin protein synthesis.
In the picture below we can see that the mRNA strand is being separated from the DNA.
Separation from DNA Strand
RNA TRANSLATION PROCESS: Process of converting mRNA to a protein
The process of Translation occurs in the Ribosome.
3 stages of Translation:
- Initiation:
- Elongation:
- Termination
- Initiation:
Each set of 3 bases on the mRNA strand is known as a Triplet or Codon and codes for a certain amino acid. For example, the codon AGU codes for the amino acid Serine.
The process of Initiation starts by building the protein by adding one amino acid at a time. The mRNA molecule will attach to a small subunit, and then they will attach together. As the small subunit moves along the mRNA molecule unit, it will find a specific nucleotide sequence on the mRNA strand with the start codon AUG.
In the model below we can see that the codons are highlighted, and the mRNA strand is placed on top of the ribosome (red cut out) and it is reading the START codon of AUG.
The start codon AUG
2. Elongation:
The amino acids are brought to the ribosome by molecules called tRNA (transfer RNA) which are represented as the green object in the model below. tRNA molecules have an amino acid at the top and an anti-codon at the bottom. The anti-codon is a set of three bases which are complimentary to the three bases on the mRNA.
The three bases on the mRNA code for the amino acids that the Trna is carrying. Each type of tRNA molecule is specific to a particular triplet on the mRNA it will ensure that it always brings down the correct amino acid.
Chain of amino acids
Once initiation takes place the charged tRNA molecule is found in the P site of the ribosome. Another tRNA finds the amino acid and then it brings it to the A site. Peptide bonds are formed between these amino acids and then the amino acids detach from the tRNA that is in the P site. Then the molecule from the A site is moved into the P site. Once the A site becomes empty this process repeats itself.
In the image above we can see that the process of elongation causes there to form a chain of amino acids.
The process of Elongation is to ensure that the TRNA’s have now brought the correct amino acids to the ribosome in the correct order so now the ribosome is able to join them together and start building up a chain of amino acids.
3. Termination:
Chain of amino acids (Primary Structure of Protein)
This procedure keeps going until a codon lacks a tRNA that matches it in the A-site. It will become a STOP codon as a result, which will stop translation.
As seen in the image above, the entire chain of amino acids will eventually separate from the ribosome and produce a protein.
Model activity questions:
1. A) Our models accurately reflect the process of Protein Synthesis because we were able to show the most important parts that are involved during this process and explain their functions through re-arranging them on a board. The hands-on aspect of this activity helped represent Protein Synthesis more accurately because we were able to show all of the stages, and document the changes made during the various stages. The objects were color-coded to make them easier to distinguish on the model.
B) Our models may have misrepresented this process because they are not as detailed as real-life Protein Synthesis, and we only included the main functions. Also, due to the time and effort required to construct the models, they are not as long or extensive as real-life models and only depict a portion of the actual process.
C) Next time, I think it would be useful to draw a model of Protein Synthesis to help demonstrate the process more accurately because a drawing could make it much more detailed, neat, and include more information. I also believe that using 3D objects rather than 2D objects would be beneficial because it can help show the proportions of the various functions involved and help explain the process more efficiently.
2. I think that these models are an effective way to engage and educate people about scientific topics since they involve different aspects of learning. These models are useful for hands-on learners because they allow them to build the model while also learning about Protein Synthesis. This model is also beneficial for visual learners because it allows them to visually see where different objects are located, and the different colored coded parts of a model can help them remember the parts of a model and retain the information for a longer period of time.
Resources:
- Class one note (Translation and Transcription PowerPoint notes, Model building activity notes)
Cited Websites:
- Study.com, 2022, study.com/academy/lesson/translation-process-location-biology.html. Accessed 22 Oct. 2022.
- “What Is Transcription? – Stages of Transcription, RNA Polymerase.” BYJUS, byjus.com/biology/dna-transcription-mrna/. Accessed 22 Oct.2022
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