Welcome to our molecular biology primer for those not initiated in molecular biology. This is not meant to be a
comprehensive review of every aspect of molecular biology
So 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 a string basically two strings in facts interwoven
Called a double helix
And they are made up of a string of nucleotides and those nucleotides are arranged in certain codes
Those codes are the code that tells 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 and
That's how they keep it straight on one side. There is a G on the other side
There is a C
And so if you know what one strands code is you will be able to figure out what the other code is
So there's also something about these DNA molecules that are important as well and that is 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 and that's important to understand because when we get out into the
Cytoplasm, that is the rest of the cell inside the cell but not in the nucleus instead of using DNA
We're going to be using RNA. So 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 a u G
C 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 deoxy ribose new clay acid
So DNA is completely different than RNA in that sense
But in another sense, it's using pretty much the same language. So it's using the language of
nucleotides so the language here is
nucleotides in the nucleus and the language here is in the script if you will of
Nucleotides it is the nucleotides that create the code
RNA generally speaking is not
Double-stranded it is only
Single-stranded and 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 5 prime end and one is
Known as the 3 prime end and then it flips around
The other one has it arranged that this side is the 5 prime end. And this side is the 3 prime end
And so what happens is there's an enzyme that's called RNA polymerase any time I say 8th at the end of anything
It's an enzyme. It's a protein enzyme. Generally speaking. So 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 that word
Transcription is the term that is used when you go from nucleotides to nucleotides
So when you're going from the nucleus information is coming out into the cytoplasm
You must transfer it 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's a five prime end. And there's also a three prime end and
What happens is they put a cap on the beginning of the five prime end to protect it?
So it doesn't start to dissolve and then there's also what we know is a poly a tail at the three prime end this RNA
with a five prime cap and a three 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. That's 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 and
When I say it's single-stranded its 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 and 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 Holley peptides or proteins or amino acids and 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 and there's a
Small and a large ribosome and there's 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's 20 different amino acids. And so tRNA with its amino acid has three codons or
Anticodons as we'll call them base pairs that fit perfectly into that code
so in other words if we were to look here and this were to be an a T a
Then we would be looking for a tRNA that has a tea a tea and it would fit perfectly in there
Bring its amino acid in and then this whole structure would then move down
three
Nucleotides till it got to another code. Let's say that that one was instead a a a
Then we would be looking for a T R and a with another amino acid. But this time the anticodon would be
TTT which would fit perfectly in there and now this amino acid would be attached to this and so as it goes down this
messenger RNA through the process of translation
we are converting the language of
nucleotides into the language of
polypeptides and so now the end process of that is a long
polypeptide with a bunch of amino acids and if you aren't aware amino acids have the chemical composition of n
CC that's one another one be n CC that's a nitrogen carbon carbon and
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's 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 changed to a valine amino
acid and that caused sickle-cell anemia
It is important that these amino acids be coded for correctly and 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 and 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 bud off you would have these proteins embedded in the cell surface
And 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
And 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 gonna take over
Transcription potentially it's good to be taking over
Translation it's gonna be taking over the use of the Golgi apparatus and the rough endoplasmic
Reticulum and its purpose is it's going to take all of these things in your cell
which is to make you have a fuller life and it's going to do one thing and that is to make more viruses and
Different viruses do it in different ways. So we're gonna talk about that now that you understand a little bit about molecular biology