Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson today on DNA replication. In this lesson today we are going to be discussing the process in which DNA is copied before a cell divides. So when a cell goes through cellular division and divides, it needs to be able to copy its DNA in order to pass copies of that DNA into the new cells that are being produced. So we call this process DNA replications.
So DNA molecules, as I mentioned, are copied so that traits can be passed from parents to offspring. So DNA polymerase is an enzyme that assists in DNA replication. So basically what this enzyme does is that it unwinds a DNA molecule and then separates the DNA so that new DNA molecules can be produced using the old DNA molecules as a template.
So let's take a look at how this works. So the first step we have here, basically this is just a DNA molecule before replication. So we have our phosphate sugar backbone. And then we have our base pairs paired up inside of here.
So what will happen is that polymerase-- we then go to our second step-- will unwind and separate those DNA molecules. So you can see how they've now been separated. So what happens then is that these old strands of DNA are used as a template in order to build new strands of DNA. So we will have new strands of DNA that will come in here and be built off of these old strands.
So they will pair up using the rules of base pairing. So if we have originally-- let's say we have adenine, thymine, and cytosine. So they're going to use those base pair rules.
So adenine always pairs up with thymine. So a thymine nucleotide will come in here. Thymine always pairs up with adenine. And cytosine always pairs up with guanine. So they're going to pair up according to base pair rules on both sides.
So then what we end up with is these new strands of DNA which are identical to the old strands. So if you take a look-- let's see-- at this strand specifically right here and this strand right here, so we have two new strands, one, two, that are both identical to our original strand. So you can see that they're identical to each other.
So this is called semiconservative replication. And what this means is that each new strand of DNA that's been produced is half old, half new. So here's the old strand. These two are the old strands that came from the original strand. And these two are the new strands that were built based off of the old strands.
So semiconservative replication means that each new strand is half old and half new. So again, though, the two strands are identical to the original. So this is how DNA is replicated so that the traits can be passed from parents to offspring.
So DNA repair is the fixing of DNA that's been damaged. And this is done by DNA polymerase. So DNA polymerase in addition to playing a role in DNA replication also helps with DNA repair. And sometimes during this process of DNA replication, DNA can change in a way that will change a gene, so a mutation can occur.
And a mutation is a change to a nucleotide sequence. So one example of a type of mutation is a base pair substitution. So there are various different types of mutations. But a base pair substitution is a type of mutation in which the wrong nucleotide pairs with a base during replication.
So let's say while replication is occurring our original strand is ATC, adenine, thymine, cytosine. And let's say during replication the adenine will pair with the thymine as it's supposed to. But then maybe the thymine will pair with guanine. So right here we have a base pair substitution, because thymine is supposed to pair with adenine, not guanine.
So it's pairing with the wrong nucleotide during replication. So that's a base pair substitution. So these mutations can occur that basically affect a gene or affect the way in which a gene is produced or functions.
So this lesson has been an overview on DNA replication and how DNA is copied prior to cell division.
A type of gene mutation in which the wrong nucleotide is paired with a base during the process of DNA replication. The effects can range from none at all to life threatening.
A change in the sequence of nucleotides in a gene.
Half of a DNA molecule produced by DNA replication is "old" coming from the original strand of DNA and half is "new" and produced using the "old" strand as a template.
An enzyme that assists in the process of DNA replication.
The process of replicating DNA before a cell divides.