DNA Modelling

Public summary: 

Play with replicating DNA

Useful information
Kit List: 

Giant DNA Model
Paper DNA print out.
There's also a DNA model in Exploring Genes which may be useful.

Packing Away: 

Lives in two silver flight cases.


This experiment takes the Giant DNA model which already existed and will create some more strands to allow replication, if you can explain how DNA is replicated please do. The model is Giant and does take up a lot of space.

DNA is made up of four bases. Adenine and Guanine are purines (fused rings) and Cytosine, Thymine (DNA only) and Uracil (RNA only) are Pyrimidines (simple rings). They're commonly refered to by the first letter. These form base pairs and stack to form deoxyriboneucliac acid (DNA) and ribonucleic acid (RNA). T and U only differ in that T has an additional methyl group. A pairs with T and C with G. Purine-Pyrimidine pairs bonded along amine and carbonyl groups. Phosphates connect successive rings of adjacent bases, these ribose or deoxyribose structures provide the backbone

There are also several paper print outs so people can make their own DNA spirals.

The first step in replication is unzipping the spiral, an enzyme called helicase breaks the hydregeon bonds holding complementary bases.
This creates a 'Y' Shape called the replication fork.
One strand is the leading strand (oriented in the 3' to 5' direction) and the other is the lagging strand (in the 5' to 3' direction) these are replicated differently.

Leading strand is replicated continuously. A short piece of RNA, called a primer, (produced by an enzyme called primase) comes along and binds to the end of the leading strand. The primer acts as the starting point for DNA synthesis. DNA polymerase binds to the leading strand and then ‘walks’ along it, adding new complementary nucleotide bases (A, C, G and T) to the strand of DNA (in the 5' to 3' direction so into the fork)

The lagging strand is replicated discontinously. Lots of RNA primers are made by the primase enzyme and bind at various points chunks of DNA are then added (Okazaki fragments) in the 5' to 3' direction so away from the fork. these fragments will need joining together later.

Once all the bases are matched up an enzyme called exonuclease strips away the RNA primers and the gaps are filled by complementary bases. It's then proofread to make sure there is no mistakes. You'll notice that in the two strands half of each is old and half new, we say DNA is semi-conservative for this reason.

You can do this replication using the model. One child is Helicase, they walk down the spiral separating it. Pick one side to be the leading strand and one person can go down and match up complementary bases following helicase, threading a rope through as they go. On the other strand someone should randomly form small segments of DNA in free location threading a small piece of rope through each section. Finally someone goes along and ties all these bits together.

Notes from exploring genes
Suggested activity 1: Play with DNA model
- DNA is a chemical which encodes genetic information, these units/words of genetic information are genes. Genes are units made of DNA
- Genes are (mostly) instructions for making proteins
- 46 DNA molecules per human cell nucleus (23 chromosomes, two of each pair, one from each parent).
- Helix is about 20 x 10-10m wide, about 2m of DNA per human cell
- Shape is double helix, as two strands wrap around each other
- Structure of double helix discovered partly from work in Cambridge (Francis Crick & James Watson in 1953, with help from Maurice Wilkins and Rosalind Franklin in London)
- Straighten out, looks like a ladder
- Sides are ladder stay the same and protect the steps - information is in variable steps of the ladder
- Colours of steps: there are only 4. 4 letters in the DNA alphabet.
- Base pairing - only certain pairs allowed. This enables one strand to act as a template for another.
- Split first few base pairs, as DNA makes a template for itself, can make two identical molecules.
- As DNA can replicate exactly, enables one cell to divide into two daughter cells with identical genetic material.
- This is how all our body cells can have the same DNA!

There's some painted hosepipes around which demo this and it's a really important part of how DNA fits into cells (and I think explains the whole 5' to 3' thingy which I don't get)

Risk Assessment
Date risk assesment last checked: 
Tue, 02/10/2018
Risk assesment checked by: 
Risk Assessment: 

People may get fingers trapped when joining DNA or splintered.
Be careful an sand edges so not splintery.
First aid.

Ropes may tangle and strangle
No running while holding model, supervise children.
First aid.

Paper cuts.
Be careful.
First Aid.