Genetics: DNA Replication


We have looked quite extensively at the structure of DNA as well as carrying out a study on the scientists who first discovered its structure and making our own models:

The three different DNA models together

The next thing the children needed to know about was DNA replication.  This would be fairly important  for their cell division lessons on Mitosis and Meiosis as the first stage of both includes the DNA replicating itself prior to cell division.

As you can see from above the DNA strand is made up of two strands joined together as a double helix by paired bases.  Before a cell divides its chromosomes needs to be replicated exactly.  This occurs by the two stranded DNA molecule ‘unzipping’, thus separating the double helix into two separate strands:



As they separate free nucleotides lock onto the bases, forming new strands.  the new, exact copies of DNA are thus formed as shown above.  GCSE bitesize have a great little animation showing this which the children viewed until they felt they fully understood.  The video can be accessed here.

I also had them watch another animation.  It was more advanced than the children needed but I still felt there was value in watching it:

We also watched the following video.  I liked this one more because I felt the animation was a little more realistic and less simplified whereas the audio and explanations were easier to understand with less information:

In order to check the children understood what they had learnt we used one of the models they had already made.  I printed out the three very simplified stages I wanted them to know onto card.  Their task was to illustrate these stages using their model:

  • The DNA spiral unzips:

Ribbet collagedna replication 1

  • Free nucleotides lock onto the bases:

DSC_0051dna replication

  • Two copies of the original DNA spiral is formed:

Ribbet collagedna replication2

This was a fairly quick and simple lesson, but was nonetheless important knowledge to possess ahead of our next two lessons on cell divisions – mitosis and meiosis.


  1. I wish I’d studied this when I was their age – it took me ages to get my head around it when it came up in my midwifery degree! If any of your children want to go into any kind of biological or health care career, this will be very useful. And if not, it’s still very fascinating!

    1. T will be going into something sciency, L wants to be a nurse or midwife and C is thinking about working with children who have learning difficulties – all of which I think will require biological sciences in some form or another. Hopefully what I teach now will set them up in good stead for the future!

  2. Thanks for including those videos, they certainly help in understanding – I know where I’ll be coming when the kids need help with their homework!

    1. Last night I was preparing today’s lesson and I said to Gary that if only we’d had these videos when I was at school I’m sure it would have made it all so much more fun! (I was bopping around to a rap about mitosis at the time. He just sat there with an affectionately bemused look on his face!)

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