What it shows
The order of bases in a gene is copied into a messenger strand, and every three bases of that strand name one amino acid. Four colours of beads show the copying and reading step by step.
The science
DNA has four bases, A, T, G and C, and pairs A with T and G with C. In transcription, one strand of the gene is used as a template to make messenger RNA, in which A pairs with U (RNA has uracil instead of thymine), T with A, G with C and C with G. In translation, ribosomes read the mRNA three bases at a time (a codon), and each codon codes for an amino acid or a stop signal. A chain of amino acids folds to make a protein.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Beads in four colours: A (red), T (blue), G (green), C (yellow)
- A fifth colour for U (white)
- Two long pieces of string or pipe cleaners
- A card with a codon table of six codons
- Small labels or paper flags for amino acids
- A ruler and glue dots
- A notebook
Safety
For this project: Beads are small parts: keep them from young children and do not put them in the mouth. An adult must supervise.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Thread a DNA template strand with beads in the order TAC AAA CCG CGA ATT, using blue, red, yellow and green beads as above.
Underneath it, build the mRNA strand by matching each base with its partner: A for T, U for A, G for C and C for G, giving AUG UUU GGC GCU UAA.
Separate the mRNA beads into five groups of three with a small card space between them to show the codons.
Use the codon table: AUG is methionine (start), UUU is phenylalanine, GGC is glycine, GCU is alanine and UAA is stop.
Write each amino acid name on a flag and attach it below its codon.
Read your finished chain: methionine, phenylalanine, glycine and alanine, then stop.
Change one base in the DNA, for example the first C in the third group, and rebuild the mRNA to see whether the amino acid changes.
Write a short note on what a mutation is and why some changes alter the protein while others do not.
What you should see
You make a DNA strand, its mRNA copy and a four-amino-acid chain with a stop signal, and see that changing a base can change an amino acid.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a codon?
A group of three bases in mRNA that codes for one amino acid or a stop signal.
2How does RNA differ from DNA in its bases?
RNA has uracil in place of thymine.
3What is transcription?
Copying a gene’s DNA sequence into a messenger RNA strand.
4What is a mutation?
A change in the base sequence of DNA.
Take it further
Make a second necklace using real codons from a short stretch of the insulin gene from a school textbook and translate it.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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