The 1952 Miller-Urey experiment determined that the Earth's antediluvian ocean conditions were volatile enough to develop the building blocks of life: amino acids. Scientists theorized that such molecules gave rise to complex life forms through biogenesis. Amino acid synthesis serves as a model for another process, one that is arguably the most important use of nucleic acids. Let's take a look.
Protein Synthesis has two major cohorts: transcription and translation.
TRANSCRIPTION
Performed inside the nucleus, transcription occurs when a DNA sequence is ''scribed" into its corresponding RNA sequence. Unfortunately, DNA is too large of a macromolecule to leave the nucleus and perform translation itself, so an RNA molecule that has the necessary nucleotides to carry out translation must be created. An enzyme (a catalytic protein) known as DNA helicase "unzips" the macromolecule, breaking the covalent bonds of the corresponding pairs (remember that A binds with T, G binds with C!), leaving the DNA unbound from its typical double helix structure. Then, another enzyme known as RNA polymerase builds a corresponding RNA molecule that should be complementary to one of the DNA strands' ends, either 5' or 3'. Remember that the RNA, now known as messenger RNA (mRNA), contains slightly different groups of nucleotides; A, U, C, and G rather than DNA's thymine.
Let's try transcribing a sequence! A 15-nucleotide long strand of DNA on the 5' end goes as following: TACCGGATACGAATT. What would the complementary mRNA sequence be? Take a minute to try it out!
If you need any help, the complementary mRNA sequence should be AUGGCCUAUGCUUAA! It's that simple! So, this particular mRNA sequence will now leave the nucleus in order to complete translation.
TRANSLATION
Once the mRNA exits the nucleus, it is ready to enter a ribosome. Ribosomes, which are scattered throughout the cytoplasm or the endoplasmic reticulum of a cell, carry out the translation process. Inside the semi-mechanical organelle, transfer RNA (tRNA) binds to the mRNA. Let's go through the process step by step.
mRNA is read in codons, which are groups of three nucleotides. These codons are essentially mRNA's scripts that will be read by the ribosome to provide and produce a tRNA molecule containing the necessary complementary nucleotides, known as an anticodon, that bind to the mRNA. Each tRNA molecule also contains 1 of 20 amino acids. This amino acid is specific to each anticodon, so in order to create the proper protein, the mRNA sequence needs to be accurate. There are two types of tRNA: initiation and elongation. Initiation tRNA contains methionine as their respective amino acid. The codon AUG signals the creation of a new protein as its complementary anticodon carries methionine, the first amino acid in a peptide. A peptide is 2 to 50 amino acids linked together through a chain known as a peptide bond. As larger peptides link together, they eventually become proteins.
After an initiation tRNA binds itself to its respective mRNA strand, the elongation tRNA enters and binds its anticodons to the respective and proper codons while also linking amino acids together. Translation ensures that the mRNA has a respective anticodon that carries an amino acid for peptide and protein synthesis.
If using the mRNA sequence above, what amino acids would we receive from their anticodons? Here is a chart to help determine that!
Using this chart (take each mRNA sequence and break it up into groups of three), we can see that our sequence from above would result in a tetrapeptide with amino acids methionine-alanine-tyrosine-alanine-stop. The stop indicates that the peptide or protein does not require any additional amino acids and can leave the ribosome to be folded, linked to other proteins, or sent to complete tasks in the cells. 11 of the 20 amino acids can be synthesized by the body naturally through a different process, but 9 are essential and require humans to consume them through their diet or supplements.
Amino acids and proteins are crucial for the body to survive and function. Changes or deletion of the genome can cause harm to cells and the body as proteins can either become deformed or cease to be created at all.
By Tyler Vazquez
National Center for Biotechnology Information. “A Mechanism for Stop Codon Recognition by the Ribosome: A Bioinformatic Approach.” PubMed Central (PMC), 1 Dec. 2001, www.ncbi.nlm.nih.gov/pmc/articles/PMC1370208/#:%7E:text=The%20termination%20factors%20are%20necessary,are%20thought%20to%20do%20this.
“Protein Synthesis (Updated).” YouTube, uploaded by Amoeba Sisters, 18 Jan. 2018, www.youtube.com/watch?v=oefAI2x2CQM&t=271s.
“What Was The Miller-Urey Experiment?” YouTube, uploaded by Stated Clearly, 27 Oct. 2015, www.youtube.com/watch?v=NNijmxsKGbc.
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