Ribosomes and the End-to-End Protein Production Line
Episode #4 of the course How the cells work by Luis Francisco Cordero
We know that we are made up of many kinds of organic molecules, but only the protein gives us our identity, our similarity with our family and other members of our species, and at the same time, our uniqueness. The lipids (or fats), carbohydrates, and other organic compounds are the same among many members of a species and even among organisms that are not related at all, while proteins are much, much more specific.
This is because proteins constitute the final product of all the information that our genetic code stores. Our DNA is composed of only four kinds of pieces, which are represented by the letters A, T, C, and G. But don’t be deceived by this scarcity of parts, because they can—and in fact, do—code all that defines you.
From Letters to Proteins
DNA blocks have their own language, and each “word” is composed of three letters, such as AGT, CTA, etc. Each of these successive words denotes which building block should be placed after another to manufacture an entire protein. Such building blocks are called amino acids.
But the protein construction process has one intermediate step, in which RNA plays the key role. DNA works exclusively to store data about which kinds of proteins should be built, but has more of a blueprint than a recipe responsibility. For amino acids to be able to assemble in the orderly fashion directed by the information coded within the DNA, this genetic data must be transferred to the very similar RNA.
Both DNA and RNA are kinds of nucleic acids, so we could say they are written in the same language. The process of making an RNA molecule from a DNA template is called transcription. At the next stage of the protein production process, the genetic information in the RNA is converted into a string of amino acids. Since nucleic acids and proteins are coded in a different “language,” this latter process is termed translation.
So, What Are Ribosomes?
After RNA has been synthesized as a copy of a specific DNA segment, it travels toward another cellular organelle that has the task to read its sequence, three “letters” at a time, and recruit one amino acid that matches that “word.” The mentioned task relies on ribosomes, and protein synthesis is of such relevance to cells, there can be millions of these little protein factories in some of them. We can think of ribosomes as assembly line workers that can read RNA instructions and attach many amino acids together to deliver proteins.
This is not the actual end of the line; many proteins require additional modification to become fully functional, but that is the role of other organelles, which we’ll discuss tomorrow.
Did You Know?
We have all heard about mutations, perhaps during scientific communications, in media news, or even in popular culture
The process of creating new DNA from a DNA template necessary during cell replication is almost perfect. But every once in awhile, the cellular machinery that performs this function commits tiny mistakes, inserting the wrong letter at some points in the chain. This is precisely what we refer to as mutations.
Often, mutations are disadvantageous for the offspring cells because the corresponding protein cannot perform its job in an adequate fashion. Other times, mutations are silent in the sense that they do not result in altered proteins. But sometimes, these random occurring mutations confer the child cell an advantage that wasn’t seen before, one that allows it to be more fit, more able to use the resources where it lives, to thrive and replicate with greater ease. Can you guess what this victory is called?
We are made of proteins, and they are what defines us as similar to our family members but unique altogether. The blueprint for their construction resides in our genetic code, and it has the ability to send copies of it to ribosomes, for such proteins to be assembled there.
Tomorrow, we will discuss how proteins can be further polished to become the marvels that underlie our cells’ every action.
The Double Helix: A Personal Account of the Discovery of the Structure of DNA by James D. Watson Ph.D.
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