Gene expression and function | Biomolecules | MCAT | Khan Academy


– So what is gene expression? Well, it’s basically the process where a gene is used to synthesize some sort of product. So you go from a gene to a product. And normally this product is a protein, but sometimes you can have
non-protein coding genes. You can create things like ribosomal RNA, actually let’s list these out. You can either have a protein, you can have ribosomal
RNA, shortened to rRNA, you can have tRNA, tRNA, you can also have something
known as small nuclear RNA. So basically you go from
a gene to a product. Now, how do we determine what the function of the gene is? How do we determine a specific gene exactly what does it do? Well, let’s imagine a
scenario where there’s a cell and normally it’s able
to if you give it milk… So lets imagine that we
give it a bottle of milk, let me just draw a little bottle of milk, it’s not the greatest
bottle in the world, but, let’s just imagine this
is a bottle of milk, so we’ll label that milk. So if you give this cell milk and normally it’s able to
take the milk and digest it and it’s able to use the milk for energy. Well, what if we wanted to figure out what gene is responsible for
being able to digest milk. Well, one thing that we can
do is if we have an idea of what gene it might be we
can just knock-out that gene. So let’s just imagine
that there’s a gene here and we imagine that
this has something to do with the digestion of milk. Well, if we knock it out and then we give milk to the cell and if it’s still able to
digest the milk then we know that this gene didn’t
really have much to do with digestion of milk. But if we knock it out and the cell is no longer
able to digest the milk, then we know that this
gene had something to do with the digestion of milk. So this process is known as a knock-out. So basically, you’re knocking out a gene and trying to figure out what the function is of the gene. So if you knock out a gene what happens to the organism? So you basically create a knock-out mutiny and study its effects. So another thing you can do is something known as reverse genetics,
reverse genetics. So here what you do is
first you start with a gene, and then you sequence it. You figure out what is
the sequence of the gene. And then what you can do is you can look for other gene sequences somewhere else in the genome that share a similar sequence. So you sequence it and then you look for a homologous sequence
somewhere else in the genome. And if you know what that homologous sequence does then you have a pretty good idea of what that gene might do. So if you know that there’s
this homologous sequence somewhere else in the genome and it goes for a specific protein, and you know the function of that protein, then you know that the gene of interest might create a protein that
has a similar function.

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