Transcription and RNA processing
Central dogma of molecular biology
- So what exactly is the central dogma of molecular biology? Well, really it could just be called the central dogma of all of life because it explains how you and I take this conglomeration of genetic information from each of our parents, and how this information gets transferred into generating a full-blown human being, like you and me. So some very clever scientists, Francis Crick and James Watson, or "Watson and Crick," as they're often referred to as, are credited with discovering this dogma, which they say deals with the detailed residue-by-residue transfer of sequential information. Or, as Marshall Nirenberg, who won the Nobel Prize in Physiology and Medicine, once said, "DNA makes RNA makes protein." And I think this simple explanation really just says it all. So let's explore this concept a little bit further. So we have three major players here. DNA and RNA are nucleic acids, which are made up of nucleotides, and proteins are made up of amino acids. And the information starts at the most basic level stored as DNA, which can then be re-stored as DNA when DNA copies itself in a process called "replication." Then DNA can be copied into RNA in a process called "transcription." And then finally you can use the information in RNA to synthesize a protein in a process called "translation." Now since DNA, RNA, and protein are linear polymers, this means that each individual unit, or monomer, is only attached to, at most, two other units. So say we have a monomer, which is just one unit. They are connected in a series like this, which makes it a linear polymer, and this is the same for DNA if each of these is a deoxyribonucleic acid, for RNA if it's a ribonucleic acid, or a protein, which are just amino acids all connected in a linear polymer. So what does this mean? This means that the specific sequence of each of these monomers effectively encodes information, and that that transfer of information is faithfully preserved from DNA to RNA to protein. Each polymer sequence is used as a template for the synthesis of the next polymer. And you could go into any step in this sequence and determine what the corresponding polymers would look like. So in other words, you could take DNA and obviously figure out what the corresponding RNA would look like, and then what the corresponding protein would look like. So this whole process is the central dogma. It can sometimes be a little bit tricky to keep all of these terms straight, so I'll try to break it down a little bit for how I like to remember them. For DNA, I think it's pretty easy. When you go from DNA, and DNA makes a copy of itself, it's called replication because DNA is just replicating itself. It's making the same copy of itself. Transcription and translation, on the other hand, it's kind of easy to get these two terms mixed up. One of them obviously is talking about DNA to RNA, whereas the other one is talking about going from RNA to protein. So if you look at the word transcription, it has the word "script" in it, so I think of it as going from one written form to another kind of written form, and both use nucleic acid, so they both use this sort of alphabet, if you will, of nucleic acids. And so you're just going from one kind of alphabet to the next kind of alphabet. Translation, on the other hand, which is also the same term that we use when translating one language to another, describes going from nucleic acid to amino acid, so it's like you're using one kind of language and going to another kind of language, because you're going from nucleic acid building blocks to amino acid building blocks. So hopefully that helps you keep these terms straight a little bit. So what did we learn about the central dogma? Just remember the simple statement that DNA makes RNA, which makes protein.