Molecular biology is quite a complex field! It entails nearly all the processes of living beings. Most students in school don’t touch molecular biology’s complexities till college. However, this subject isn’t as convoluted as it seems. You just need to understand a simple concept to enter the world of molecular biology: its central dogma.
According to pediaa.com, the central dogma of molecular biology “describes the process by which the information in genes flows into proteins”. That’s pretty much it! Of course, it’s more complex than a single sentence, as we’ll see later in this article.
What does this “central dogma” do? It’s responsible for a vital function: making proteins. Proteins are essentially the building blocks of organisms. They make up tissues, genetic material, membranes, enzymes, and much more.
The central dogma of molecular biology can be split into 2 key terms:
transcription
translation
Let’s take a deeper look at each term.
Transcription
To us, transcription is the process of rewriting something, like a voicemail. Our cells do something similar. In their case, the DNA is like the voicemail, DNA nucleotides are the words, and the mRNA is a sentence made from these words.
Transcription is like the trigger behind this entire process. It essentially involves double-stranded DNA being copied onto mRNA (messenger RNA). It has 3 stages: initiation, elongation, and termination.
Initiation: Transcription is initiated by an enzyme called “RNA polymerase”. DNA is woven through the RNA polymerase till a certain section of it touches the enzyme. That section is called the promoter. Upon contact with the promoter, the DNA is split into 2 strands, as seen below.
Elongation: Now that the DNA is split, the cell has a template of nucleotides for the RNA. At the top is a coding strand, and at the bottom is a template strand. RNA is then threaded into this gap and run over the template strand. Complementary nucleotides are then copied onto the RNA. For instance, if the nucleotide structure of the DNA is ACTG, then the RNA would gain UGAC nucleotides. (Note that thymine doesn’t exist in the case of RNA. Thymine is replaced by another nucleotide called “uracil”.)
Termination: This is the last phase of translation. At this stage, an entire strand of mRNA has been made. The RNA polymerase passes through a sequence on the DNA called the terminator. This induces the release of the mRNA from the RNA polymerase.
Translation
Translation is essentially the process of turning the mRNA sequence into a polypeptide. The cell reads the nucleotides in groups of 3, called codons. These codons specify different amino acids. For instance, the codon AUG encodes methionine (an amino acid).
So how are these amino acids made? tRNAs are the agent behind this process. They connect the codon to one of its own anticodons (which are the complementary nucleotide sequences of the codon). There are many different types of tRNAs that form different amino acids. tRNAs have an asset called the ribosome. Polypeptides are built in the ribosome. The ribosome surrounds the mRNA so that the tRNAs can find their respective codon through slot-like structures.
Here’s an animation of the process of translation:
This simple process is not just the heart of molecular biology, but also a crucial mechanism that lets us survive. To sum it up, transcription and translation form both the central dogma of molecular biology and an array of vital proteins and polypeptides.
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