String Genome

DNA is at the heart of evolution and is the code of life. What do we know about this molecule? How long is DNA? If all the DNA in our body was laid end to end, how far would it reach? What percentage of the DNA in our cells encodes proteins?

Student Learning Goals:

  • Students will observe that DNA is very long , very skinny, and packs well into cells.
  • Students will learn that only a small fraction of the DNA in our cells encodes the approximately 23,000 genes.
  • Students will be able to discuss the usefulness and limitations of this model.

Introduction:

The human genome contains about 3 billion nucleotides, about the same number of nucleotides as mice, apes and most other mammals. If you were to unravel the DNA packed into all 23 pairs of chromosomes in just one of the of your cells, how long would that stretch of DNA be? It would be 2 meters long!   Two meters multiplied times 10 trillion cells in your body is a length of DNA to go to the sun and back almost 70 times!

Materials Per student:

  • 2 meters black yarn
  • 2 cm length of sticky-backed labels (in blue to represent “blue genes”)
  • (optional:  add 5 cm red sticky backed labels to represent “red regulators”)
  • scissors

Tell the students to cut the labels into 23,000 pieces to represent the 23,000 genes in our genome. SMILE :-) .   If their scissors are not sharp enough to do this, they may cut the labels into about a dozen pieces. These are then stuck onto the string in a distributed fashion.

This string is mostly black, with a little red and a little blue.  The blue region represent genes. Only about 1 percent of the human genome encodes gene.  The red represents control genes or regulatory elements that regulate when genes are turned on or off.   The black is very interesting.  It represents the so called “dark matter” or what some call “junk” in our genes.