Cut-Out DNA TEACHER NOTES

Modelling the Helix

Cut-out DNA TEACHER NOTES

· KS5 desk activity

· Collaboratively make an accurate paper model of DNA structure

Prior knowledge:

o What is DNA (why is it important/interesting)

o Understanding of chemical symbols and drawings of molecular structure

Introduces:

o DNA structure; hydrogen bonding of A/T vs G/T; major and minor groove

Materials (for each participant):

o Photocopies (onto card) of nucleotide templates (colour or black & white) , 1-3 per student.

o Coloured pencils (if printing in black & white)

o A thick needle or similar for punching through card

o Scissors

o Option: a sharp craft knife

o Paper glue

o Drinking straw

o Fine string or strong sewing thread

We suggest the teacher/presenter has a trial run to make sure they are familiar with the folding method and resultant structure.

Activity:

The class should collaborate on one model. Each student should make just one or two base-pairs; they are likely to lose interest after this.

It takes ten nucleotide pairs for one turn of the double helix, and at least 16 to show the major and minor grooves.

Instructions for assembly are given on the Instructions sheet.

Assemble the DNA strand as you go along, checking that it has the correct handedness.

You may wish to oversee the attachement of each base-pair to ensure they are correct. This is most important for the first ones in the chain.

Acknowledgement

Thanks to Dean Madden for allowing us to share this activity. Dean developed this model having been inspired by an earlier, similar model by Van Rensselaer Potter (1958). Activity & images © Dean Madden 2008

Modelling the Helix

INSTRUCTIONS

Prepare your base-pair:

Colour the template before cutting it out: Cytosine=Blue; Guanine=Yellow; Adenine=Green; Thymine=Red
Cut around the thicker, outer lines.
Make two small cuts into the card by the phosphate groups where indicated. Optional: use a sharp craft knife to make cuts above the oxygen of the deoxyribose molecules where shown.
Carefully punch a small hole in the cut-out where shown. This will be the axis of the DNA model through which the string will be threaded. Don’t make these holes too big!
Fold the sugar-phosphate ‘backbones’ where indicated by dotted lines, as shown below. These folds must be made in the directions shown.

Add your base-pair to the model:

Cut an exactly 25mm long piece of drinking straw.
Orient your base-pair the same way up as the others in the growing chain.

Remember that the sugar-phosphate chains run in opposite (anti-parallel) directions

Thread the end of the string through the drinking straw, and then through the hole in your base-pair.
Glue the phosphate group on the end of the chain to the deoxyribose of your base-pair. Do the same with the opposite sugar–phosphate strand. The orientation of the letters on the card should help you to assemble the model correctly.

Complete the model (when all base-pairs have been added):

Cut out the genetic code discs, and glue the two sides together onto the string at the bottom of the model. The weight of the discs will help the model to hang vertically.

Modelling the Helix TEMPLATE 1

Modelling the Helix TEMPLATE 3

You need only one copy of this per model.

Modelling the Helix TEMPLATE 4

You need only one copy of this per model.