Up Learn – A Level Biology (AQA) – DNA and Cell Division
Semi-Conservative DNA Replication – Part 2
Semi-conservative DNA replication uses DNA helicase and DNA polymerase to create two ‘template strands’ from a single DNA molecule, which are then formed into two new molecules of DNA.
More videos on DNA and Cell Division:
Semi-Conservative DNA Replication – Part 1
Semi-Conservative DNA Replication – Part 2
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DNA and Cell Division
2. The Three Models for DNA Replication
3. Nitrogen and Centrifuges
4. Nitrogen for DNA Replication
5. The Meselson-Stahl Experiment Part 1
6. The Meselson-Stahl Experiment Part 2
7. Semi-Conservative DNA Replication Part 1
8. Semi-Conservative DNA Replication Part 2
9. Common Mistakes in Exam Questions
10. Benefit of Semi-Conservative Replication
Previously, we’ve seen that in the first step of DNA replication, the enzyme DNA helicase breaks the hydrogen bonds between DNA bases…
Breaking the two strands apart and exposing the bases on each strand.
Then, DNA nucleotides in the nucleus are attracted to complementary bases on the strand…
And hydrogen bonds form between them.
Next, once a few nucleotides have formed hydrogen bonds with their complementary bases, another enzyme, DNA polymerase, attaches to each strand like this.
There, DNA polymerase joins the nucleotides together using a condensation reaction
This reaction forms a…
This reaction forms a phosphodiester bond between adjacent nucleotides.
So now, these nucleotides are joined together…
And two new strands are beginning to form.
Next [3 second pause in audio], DNA helicase continues to break hydrogen bonds between complementary bases…
DNA nucleotides continue to be attracted to complementary bases on the exposed strands…
And DNA polymerase continues to join the nucleotides together.
Then, once the last nucleotide is added to each strand [ 3 second pause in audio], and all enzymes detach…
We’re left with two, completely identical, DNA molecules…
Which coil to form two helixes!
To sum up, in the first step of DNA replication, the enzyme…
In the first step of DNA replication, the enzyme DNA helicase breaks the hydrogen bonds between DNA bases…
Breaking the two strands apart and exposing the bases on each strand.
Next…
Next, DNA nucleotides in the nucleus are attracted to complementary bases on the exposed strand…
And new hydrogen bonds form between the complementary bases.
Then, the enzyme DNA polymerase attaches to both strands and joins the nucleotides together using a…
Then, the enzyme DNA polymerase attaches to both strands and joins the nucleotides together using a condensation reaction
This reaction forms a phosphodiester bond between adjacent nucleotides.
Both enzymes then continue to move along the DNA molecule…
Until finally, we’re left with two identical molecules of DNA which coil to form two helixes!