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DNA Dance©

 

or, How to Build a Human DNA Model--Out of Humans.

 

The Human DNA Model demonstrates three key ideas of the Watson-Crick model of DNA:

1. DNA is double-stranded;

2. The two strands are complementary;

3. The two strands are antiparallel.

 

The Human DNA Model does not show the fourth key idea of the Watson-Crick model: DNA is helical.

 

However, the Human DNA Model is among the easiest ways to show the idea of "antiparallel" because the two lines of people face opposite directions as they shake hands, like two teams after a baseball game. Few models of DNA actually show the antiparallel nature of DNA, and of the models that do show the antiparallel aspect, most do not make it easy to see that the strands are heading in opposite directions. This one does.

 

Tom Zinnen, UW Biotechnology Center and UW-Extension, 608/265-2420

Objective: To demonstrate how DNA is structured, copied, spliced and read. DNA Dance is demonstrated in the SERC Biotechnology workshop tape from October 20, 1993 (session 1). To order the entire series or any combination contact: Tape Dubbing Service, Wisconsin Public Broadcasting, (608) 264-9701. Copyright ©1992. Tom Zinnen, UW Biotechnology Center. Permission for non-commercial, Outreachal use is hereby given.
Students will understand that:
  • DNA is composed of 4 nucleotides, or building blocks: A, T, G and C
  • These building blocks can be strung together (to carry a message).
  • A single string can be paired with another string (its "mate" or "complement"), to make double-stranded DNA (given A matches with T and G matches with C).
  • The order of nucleotides in one strand will determine the order of its mate.
  • The two mate strands face in opposite directions.
  • The order of the building blocks can be used to make three-letter words that can code a message;
  • DNA can be copied by "unzipping" the original double strand and filling in the two separated strings or strands with spare building blocks.
  • A new piece of DNA can be spliced into another piece of DNA to give new messages.
What to do:
1. Divide students into 4 groups: A, T, G, C.
sticka stickt
stickg stickc
2. Assign the rule that A's go to T's and vice versa; and G's go to C's and vice versa. (Matching rules or bonding rules or Chargaff's rules).
3. Assign the position so each person's left arm is extended to the front, and right arm is extended to the side (in a top view, the arms form an L: the "L" position). The left arm is like the phosphate in a DNA nucleotide; the body is like the deoxyribose in a DNA nucleotide; and the right hand is like the nitrogenous base in a DNA nucleotide. The left shoulder serves as the 3' carbon of the deoxyribose, to which attaches the phosphate from the next nucleotide (the left hand of the next person behind). The right shoulder serves as the 1' carbon of the deoxyribose, to which is attached the base (the right hand).
top
4. Assign configurations for the RIGHT hand: THIS IS A KEY STEP
ohand C's curve their hands partly open. point T's make a hook by extending a curved index finger;
fist G's make a fist; chand A's make an "OK" sign by touching their index finger to their thumb;
Note that these are designed so A's and T's can match or interlock, and so can G's and C's. Other combinations are more awkward.
5. Mix the students so that all four types are mingled. stickmixstickmix
6. Randomly pull out 1/3 of the group, and line them up, left hand of one on the left shoulder of the next person ahead, right arm extended to the side, right hand in the appropriate configuration.
conga
7. Now let the other 2/3 of the group assume the L position and the right hand configuration. Form a second line by joining the right hands of students in the second line with the right hands of the students in the first (template) line.
dance

Note that this second line will face in the direction opposite of the original. Also, note that its sequence will be complementary to the first (but the two strands are NOT a mirror image of each other).

 

You can show how DNA can melt into two single strands by asking the two lines to release their handshakes and take one step to the left, while keeping their right hands in the C, T, G or A form. You can show how two complementary single strands of DNA can anneal (come together) by then having the two strands come back together into a double-stranded form.

You can copy DNA by splitting the two-stranded line, and filling in at the "fork" where the split is initiated. Cutting and splicing and most other DNA manipulations that depend on sequence and antiparallelism (but not on helical aspects) can be demonstrated using this dance analogy.