GENES X They are in you and in me; they created us, body and mind; and their preservation is the ultimate rationale for our existence. They have come a long way, those replicators. Now they go by the name of genes, and we are their survival machines.” Richard Dawkins (from The Selfish Gene, 1976)

They are in you and in me; they created us, body and mind; and their preservation is the ultimate rationale for our existence. They have come a long way, those replicators. Now they go by the name of genes, and we are their survival machines.”

Richard Dawkins (from The Selfish Gene, 1976)
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From information to objects.

Genes are the blueprints for bodies. But if a gene is a unit of information, how do we go from something as ethereal as information to something as concrete as a body? 

The answer: DNA (the stuff of genes) is transcribed into RNA which is translated into proteins (the stuff of bodies) (1). This is called the “Central Dogma” of molecular biology, which is an unfortunate name. It should be called the “Central Theory”, because it is one of the most robust findings in all of biology. Also, it is thoroughly anti-dogmatic and many refinements and caveats have been issued since Francis Crick first put it into words

//////////////////////////////////////The foreign language is the genetic code; the idea is the body.

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The Twisted Ladder: DNA and Base Pairing

Picture a tiny ladder, then pinch both ends and twist it. You now have a twisted ladder. Next, take a tiny hacksaw and cut every rung of the ladder in half, producing two half-ladders. Now glue each of those freshly cut half rungs back together. 

Using a tiny engraving tool, mark all of the half-rungs, but for only one of the half-ladders. Each half-rung gets only one mark, and it must be either “A”, “C”, “G”, or “T”. Now you have your twisted, glued-together, half-ladders, one half of which has letters engraved on its half-rungs. 

Flip it around, focusing on the half that doesn’t have engravings on its half-rungs. Now start engraving those, following this rule: an “A” half-rung can only be paired with a “T” on the opposite half-rung. Likewise, “C”s only go with “G”s. 

Remember: A with T, C with G. 

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The code: Genes are coded representations of proteins.

We now have a toy model of DNA, with its double helical structure. To put this model into perspective, understand that the human genome has three billion rungs (2), or “base pairs” (“pair” because each half-rung, or letter, is a “base” molecule).

The human genome has three billion base pairs.

////////////////////////////certain three-letter combinations of As, Ts, Cs, and Gs stand for certain amino acids, the basic units of proteins (this will be explained in future installments of this series). 
Genes stand for proteins, just as sentences stand for the ideas they convey.

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RNA: Middleman between gene and protein

Genes stand for proteins, just as sentences stand for the ideas they convey. But as we said above, the DNA sentence is metaphorically written in a foreign language, so how do we read it?

To extract meaning from a foreign sentence we would need to first transcribe it into our native tongue, then feed it into our language decoding machines (our brains). 


////////////////////////In the case of genes, we need to transcribe the code (written in the language of DNA) into a slightly different language (that of RNA) so that the meaning can be extracted–the protein can be produced–by a molecular machine that only understands RNA-ese. 


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RNA serves as the intermediary between DNA and proteins, but why would cells not just use a single genetic language? DNA is precious to your cells. If damaged, cancer, disease, and death can result. Each cell has only one copy of its DNA, so it’s crucial that when we make proteins we do not put the DNA in jeopardy. 

That is one reason why we need RNA. It is a cheap copy–or “transcript” (a technical term)–of the code in DNA (plus, as mentioned, the protein-building machine only reads RNA).

It’s crucial that when we make proteins we do not put the DNA in jeopardy. 

/////////////////////////////////RNA and DNA are similar, with two notable differences. First, RNA is single stranded (a half ladder with half-rungs protruding from it). Second, RNA uses the base “U” instead of “T”, but both have the same function of pairing with “A”. These structural and grammatical distinctions are the main differences between the language of DNA and RNA.

So how do we transcribe a message written in DNA into one written in RNA? We need a scribe who can read DNA and write RNA.

The Scribe: RNA Polymerase makes RNA out of DNA

////////////////////////////////////////In the case of genetic information, this machine is called a “ribosome”. RNA transcripts are fed into ribosomes which pump out proteins

////////////////////////Life started with a single molecule, or a collection thereof, which had to do two things: harness energy from the environment to power chemical reactions (metabolism) and replicate with fidelity and regularity (inheritance).

//////////////////In fact, RNA is a dual-capacity molecule. RNA molecules carry information (like DNA) and some can also carry out enzymatic functions (like proteins). This discovery won Thomas Cech and Sidney Altman the 1989 Nobel Prize in chemistry (7), which gave way to an intriguing hypothesis about the enigma of all enigmas: the origin of life. 

////////////////////////////Whether or not the “RNA world” hypothesis is true, the fact that RNA can be both enzyme and replicator is a testament to the craftiness of evolution. While RNA may be neither as good at storing information as DNA, nor at catalyzing reactions as proteins, its dual-capacity is evolutionarily valuable nonetheless. It allows cells to complete certain tasks with unmatched efficiency, like an RNA transcript of a gene able to edit (i.e. “splice”) itself

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