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Science Made Simple: #2 | Gene Expression: How Your DNA Becomes Your Appearance

Today, it’s common sense that ‘DNA is the genetic material’. Many of us are aware that our DNA determines our physical appearance, yet we rarely talk about how that determination proceeds.

In this article, we will be answering the question how.


Before that, though, we need to discuss some introductory information so that all of us are able to grasp the topic better:

You, and me, like all the other living organisms on Earth, are made up of billions of tiny, yet complex cells. Inside these cells resides our DNA, or deoxyribonucleic acid, a double-stranded molecule which contains all of the crucial information about how we look like, the ways we grow and develop as an organism, and the unique features we have as unique living beings. These unique ‘information’ or ‘instructions’ stored in the DNA corresponds to the unique numbers and orders of complementary base pairs that constitute the DNA itself, the pairs being adenine to thymine and guanine to cytosine. The differences between the DNA’s of different humans are explained by the differences in the sequence of these pairs.

Genes, on the other hand, are certain segments of your DNA by which the ‘unique information’ about you stored in your DNA is expressed and rendered visible to the outside world. Different genes may hold different functions: some are responsible of producing functional material in order for the genetic information to be expressed while some do not code for functional material, yet regulate the production process.



Now that we’ve covered the basics, let’s dive deeper into understanding the structure of our genetic code and the ways it appears in our lives, starting to discuss how the expression of genes works. The process of gene expression refers to the production of a functional molecule from the ‘unique information’ stored in the protein-coding genes, and occurs in two main steps:


Transcription

The transcription process is where the ‘information’ on a certain protein-coding gene coded by base pairs is copied to a single-stranded molecule known as the messenger RNA.

The term RNA refers to ribonucleic acid, a molecule that is generally known to be single-stranded and contains the same chemical bases as DNA on it, the only exception being uracil instead of thymine. The messenger RNA (or mRNA for short) carries the required instructions to produce the said functional molecule in gene expression. With the help of an enzyme called RNA polymerase, free chemical bases are arranged accordingly, hence the mRNA is synthesized.



Translation

As its name suggests, translation is the process in which mRNA brings the ‘instructions’ it carries to the ribosome (an organelle in our cells that functions in synthesizing proteins) and those instructions are ‘translated’ into a functional molecule, which is in this case, a protein molecule.

Here, we encounter another unique RNA molecule: transfer RNA, or tRNA for short, which is responsible of carrying amino acids, building blocks for protein molecules, to the ribosome so that a protein molecule can be synthesized. A magnificent feature of tRNA’s is that they carry a sequence consisting of three chemical bases called anticodons, and the amino acid they carry on them are determined according to that specific anticodon. Moreover, the anticodons are complementary with certain three-base sequences on the mRNA that , which are called codons (See the image above).

The protein molecules that are synthesized at the end of these two steps of gene expression determine your phenotype, a term collectively referring to your physical traits.


Here was an overview of how the genetic information stored in your DNA is expressed and transformed into features of your physical appearance.

If you found the concept of gene expression interesting, this article encourages you to do further reading on the topics:

  • gene regulation

  • post-translational modifications

  • codon charts

to gain a more detailed insight on how genes work and dive even more deeper into the field of genetics.


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