Molecular Biology Primer – How Viruses Work
Welcome to our molecular biology primer. For those who have not initiated in molecular biology, this is not meant to be a comprehensive review of every aspect of molecular biology.
Every cell has a nucleus, and it is in the nucleus that you have DNA. DNA codes for the different types of proteins that are used in the nucleus, and DNA is basically two strings interwoven, called a double helix. They are made up of a string of nucleotides, and those nucleotides are arranged in certain codes. Those codes tell you exactly what your protein is going to be when you are done.
A T G and C are the letters that the nucleus will use as a code that will be translated into proteins and protein synthesis. So in the DNA, because it is double-stranded, if on one side there is an A, then the other side must be binding to a T. That’s how they keep it straight on one side. There is a G on the other side, there is a C. So if you know what one strands code is, you will be able to figure out what the other code is.
A, T, G和C是原子核将用作编码的字母，这些字母将被翻译成蛋白质和蛋白质合成。因此在DNA中，因为它是双链的，所以如果在一侧有一个A，那么另一侧必须与T结合。这就是他们如何使其在一侧保持笔直。另一面有一个G，一个C。因此，如果您知道一个代码串是什么，那么您将能够弄清楚另一个代码是什么。
So there’s also something about these DNA molecules that is important as well. On every single one of these nucleotides, there is one less oxygen than would normally be. That’s why it’s known as deoxyribonucleic acid. That’s important to understand because when we get out to the cytoplasm, which is the rest of the cell and inside the cell, but not in the nucleus, instead of using DNA, we’re going to be using RNA.
RNA is exactly the same as DNA except for two major areas. RNA will use exactly the same letters, except it will not use a T, it will use a U, so it’s AUGC. U stands for uracil. The other thing about it is that in that area where there is no oxygen, there actually is an oxygen, and that’s why it’s known as ribonucleic acid. And this is known as deoxyribonucleic acid. So DNA is completely different than RNA in that sense.
除了两个主要方面外，RNA与DNA完全相同。 RNA将使用完全相同的字母，除了不使用T，将使用U，所以它是AUGC。 U代表尿嘧啶。另一件事是在那个没有氧的区域，实际上有一个氧，这就是为什么它被称为核糖核酸的原因。这就是所谓的脱氧核糖核酸。因此，DNA在这个意义上与RNA完全不同。
But in another sense, it’s using pretty much the same language. It’s using the language of nucleotides. The language here is nucleotides in the nucleus, and the language here is in the script if you will, of nucleotides, it is nucleotides that create the code.
RNA generally speaking is not double-stranded; it is only single-stranded. So what happens here is that this is the master blueprint. That is the DNA. And what happens is that this DNA opens up, and I’ll show you here what it looks like. So imagine this is a strand here of DNA. It opens up and there is a direction to these ends. (Just go with me on this one.) One is known as the five-prime-end, and another is known as the three-prime-end. Then it flips around the other one has it arranged so that this side is the five-prime end and the other side is the three-prime-end.
So what happens is there’s an enzyme called RNA polymerase. Anytime I say ASE at the end of anything, it’s an enzyme, and it’s a protein enzyme generally speaking. RNA polymerase is the enzyme that polymerizes RNA together. So here we have this RNA polymerase that’s on the DNA, and it’s traveling in this direction, and as it goes over the different nucleotides, boom-boom-boom-boom-boom, the different nucleotides and this is all happening in the nucleus, it starts to pull in different nucleotides that are available to make a long string of RNA.
Because we’re going from the language of nucleotides, nucleotides being the language here, because we’re going from nucleotides again back to nucleotides, that is not a change in the language of the code. That is simply a transcription of the code. It’s like we’re photocopying almost, so transcription is the term that is used when you go from nucleotides to nucleotides.
When you’re going from the nucleus, information is coming out into the cytoplasm; you must transfer from DNA into RNA. And generally speaking in human cells, there’s no way to really go from RNA back to DNA. This is a unidirectional thing. So in other words, the code is always kept the same, generally speaking. It is copied in the process of transcription, and you go from a copy of the DNA, making a copy of the RNA.
Here we have the RNA. There’s something that happens to the RNA. There is a five-prime-end and there’s also a 3-prime end, and what happens is they put a cap on the beginning of the 5-prime-end to protect it, so it doesn’t start to dissolve. Then there’s also, what we know, is a poly-A tail at the 3-prime-end.
This RNA with a five-prime cap and a 3-prime poly-A tail is known as a special type of RNA, known as messenger RNA. Why is it called messenger? Because it’s sending out a message from the nucleus into the cytoplasm about what needs to happen next. In other words, it has the grand blueprint for the entire cell, and it’s saying here are the plans for this portion of the cell that I want to build, and here is the message that’s coming from the central portion of the nucleus, which is known as messenger RNA.
So this messenger RNA now has a bunch of nucleotides. Of course, now it’s using slightly different letters. It’s using the A; it’s using the C; it’s using the G. But instead of a T, it’s using a U, and it’s single-stranded. When I say it’s single-stranded, it’s single-stranded because it is ready to be translated. In other words, we’re now going to switch into a different language. Instead of nucleotide-base pairs, we’re going to be switching into the language of proteins. Proteins, if you don’t know, are made up of amino acids, and so we’re going to be going from the language of nucleotides to the language of Holly peptides, or proteins, or amino acids. That’s known as not transcription, but rather translation, because it’s a different language.
And so what happens here is that you get a ribosome. A ribosome sits back on here. There’s a small and a large ribosome and there are some spaces here for another kind of RNA to come along. That’s been made before and that is a tRNA. What’s the purpose of a tRNA? There are many many, many different types of tRNAs. All of which are bound to it to have an amino acid, a different amino acid. There are 20 different amino acids.
So tRNA with its amino acid has three codons, or anticodons, as we’ll call them, base pairs that fit perfectly into that code, and it would fit perfectly in there and bring its amino acid in, and then this whole structure would move down through three nucleotides till it gets to another code, and now this amino acid would be attached to this, and so as it goes down, this messenger RNA, through the process of translation, will convert the language of nucleotides into the language of polypeptides.
Now the end process of that is a long polypeptide with a bunch of amino acids. If you aren’t aware, amino acids have the chemical composition of N-CC; that’s one. Another one NCC; that’s a nitrogen-carbon-carbon, and N-CC. These polypeptides, these proteins, do everything in the cell. These are the proteins that can, for instance, make hemoglobin that binds oxygen. These are the proteins that are going to be involved in cellular respiration like glycolysis.
So you have a whole bunch of these enzymes and proteins, and there are hundreds of thousands of different proteins. If you want to move your muscle, guess what? That’s an interaction with actin and myosin. Those are all proteins that are made, and they all have a specific shape and size, and it’s very important that those proteins look exactly the same.
If that one amino acid changes, then the whole protein may not work. So this is what happens in sickle cell. Anemia is when you have a glutamic amino acid getting substituted and change to a valine amino acid, and that causes sickle cell anemia.
It is important that these amino acids be coded for correctly. That is what happens with transcription and translation. These proteins can be made in different ways. You can have a ribosome making on a messenger RNA, a protein which just goes into the cytoplasm; or you can have these proteins arrange themselves on cellular structures like the rough endoplasmic reticulum and the Golgi apparatus, in which case these proteins will be embedded in these organelles. When they go and fuse with the cell surface, they will actually put the protein in the cell surface so that if it were to butt off, you would have these proteins embedded in the cell surface.
This is important because viruses will use all of this to make more viruses because viruses have proteins inside of them that have to be made again, and viruses have proteins on their cell surface that have to be made again. So depending on where the virus wants those proteins to be made, then it’s going to basically direct those proteins and ribosomes to either the Golgi apparatus or the rough endoplasmic reticulum, or just to be made in the cytoplasm itself.
The reason why I bring all of this up is because what a virus is going to do when it infects a cell is it is actually going to take over the machinery of this cell. So it’s going to take over transcription, potentially. It’s going to be taking over translation. It’s going to be taking over the use of the Golgi apparatus and the rough endoplasmic reticulum. Its purpose is going to take all of these things in your cell, which is to make you have a fuller life. It’s going to do one thing, and that is to make more viruses and different viruses and do it in different ways. So we’re going to talk about that.
Now that you understand a little bit about molecular biology, it’s going to make sense. So, please join us for our update where we talk about the coronavirus and how it invades the cell, and does what it does. We’ll talk about other viruses, and we can compare and contrast. Thanks for joining us.