This one takes a little prep work the first time 'round. But after that, you're set forever. It's a great way to include a little kinesthetic activity into the study of DNA.
First, the prep work:
On a long strip of paper* write out a string of DNA bases (actually, you're making the mRNA). You want to make sure your letters are evenly spaced - I actually marked the paper.
Keep a codon chart handy - make sure you begin with a start codon and don't come to a stop codon immediately. And, don't make the mistake of using T instead of U, as someone did...
Now you need to make a ribosome through which your strip of paper can fit. I made mine out of fun foam. It has magnets on the back, so it sticks to the white board. Cut the window in the ribosome, so that you can see 3 bases at a time (hence the reason for evenly spacing your letters). Use this picture to guide you:
Now you need to make the amino acids. Once again I used fun foam. I wrote the amino acid on the foam, punched holes in it and strung string through the holes so the students could wear them.
For the activity:
Draw a huge circle on the board - a cell. Sketch in a nucleus and stick your ribosome in the middle as well.
Show your students the mRNA (your paper strip) moving from the nucleus to the ribosome.
Feed the mRNA into the ribosome.
Have your students translate the first 3 mRNA bases into an amino acid.
Have a student put the appropriate amino acid placard on and stand in front of the room.
Move the mRNA to the next three bases. Determine the amino acid. Have another student put on the appropriate placard, then stand next to the first student and hold his/her hand.
Proceed this way until you come to a stop codon, or until you've made your point.
Your students will have a better feel for how a ribosome translates mRNA, how proteins are formed, and understand that proteins are long chains of amino acids.
* I got a few sentence strips from an elementary teacher in my building - they're the perfect size and shape for this, I didn't have to cut them, and they have lines marked on them!
I learned this from a fellow teacher at a NJ Science Teachers Association Convention several years ago. I don't know who that teacher is - but if you're out there, please let me know - I'd like to give you credit.