LESSON 19
 

The Race for the Double Helix



Authors:

An edited version of a classroom lesson initially authored by the following Long Island, NY science teachers:

Steven Angell and Marcia Brandeau, Longwood High School, Middle Island

James Baglivi and Mary Loesing, Shoreham-Wading River High School, Shoreham

Theresa Dana, Deer Park High School, Deer Park

Jack Waszmer, Paul Gelinas Junior High School, Setauket
 

Courses for Which the Lesson is Intended:

Intended for use in a college-preparatory or advanced high school biology course.
 

Types of Teaching/Learning Activities Employed in this Lesson:

Students work in collaborative groups.

Students are required to use knowledge from the course to solve a puzzle.

The class watches a video.

The teacher leads a student discussion of the ethics/values issues associated with the student activity and the events depicted in the video.
 

Category that Best Describes this Lesson:

Behavior of scientists.
 

Ethics/Values Issues Raised by this Lesson:

Cooperation versus competition in science; attitudes toward the sharing of unpublished data and results; assignment of credit for scientific discoveries; sexual bias in the scientific community.
 
 

Lesson Plan


Instructions for the Teacher:

This lesson is designed to explore several common ethics/values issues related to the behavior of research scientists, while reinforcing students' understanding of the relationship between the structure of the DNA molecule and the biology of protein synthesis. It was inspired by the video The Race for the Double Helix(55), which is a dramatization of the efforts of James Watson, Francis Crick, Rosalind Franklin, Maurice Wilkins and other scientists that led to the discovery of the structure of DNA. The video is, in turn, based on the book The Double Helix, by James Watson(56).

The complete activity requires a minimum of four forty-minute class periods. It should be used after students have learned about the structure of DNA, the relationship between DNA and messenger RNA (mRNA), and the mechanism of synthesis of proteins using mRNA.

At the beginning of the lesson, the class is divided into groups of four students each representing a "research team." The objective of these teams is to win a "bonus" by deciphering a coded message. This is achieved by first transcribing a DNA segment, given to the team, into mRNA, determining the amino acid sequence that is coded on the mRNA, and then using a code that assigns each amino acid to a letter or other element of sentence structure.

No single research team is given enough information to decipher the entire message. Each team is given instructions on how to interact with the other teams in an effort to win the bonus. Some of the teams are instructed to behave in a collaborative manner, sharing their information. A second set of teams is told to act in a highly competitive manner, keeping their own results to themselves while aggressively attempting to obtain data from the others. One team is instructed to work independently and methodically in an effort to solve the problem on its own.

The following instructions are based on an assumed class size of 24. The six four-person research teams will be labeled Groups A, B, C, D, E and F. Groups A, B, and C will be instructed to behave as "collaborator" teams. Groups D and E will be told to behave as aggressive "competitors."  Group F will be the "independent," methodical research team. (In classes of larger or smaller size, some, or all of the groups can be increased to five or decreased to three students. Alternatively, the number of collaborator or competitor groups can be increased or decreased.)

The first group that brings the correct message to the teacher wins the bonus. That message is "CONGRATULATIONS! YOU ARE THE WINNER. THE BONUS IS YOURS!"
 

The segments of DNA given to each of the groups, when correctly decoded, will produce the following partial messages:
 

Group A: ___________________! YOU ___ ___ WINNER. THE ______ IS YOURS!

Group B: ___________________! YOU ARE THE ________. ___ BONUS __ ______!

Group C: ___________________! YOU ___ ___ WINNER. THE ______ IS ______!

Groups D&E: ___________________! YOU ARE THE WINNER. ___ ______ __ ______!

Group F: CONGRATULATIONS! YOU ARE THE WINNER. THE BONUS IS SCAT!
 

Note that by exchanging data, the collaborator groups can get the entire message, except for the first word, which they would have to guess. The independent group has a longer message, which includes the first word, which none of the other groups have. By working methodically on their own that group can get an entire message, but the last word is incorrect and they can get the bonus only by guessing the correct word. The competitor groups are given the shortest part of the message, but by following their instructions to be aggressive, they may be able to find a way to get the rest of the information. In fact, teachers who have used this exercise report that it is usually one of the competitor groups that wins the bonus.

After one of the groups correctly deciphers the message, the teacher should lead a discussion about the students' reaction to the activity and their thoughts about how the instructions given to the groups compare with what they imagine to be the behavior of real-life scientific researchers. The teacher should help the students identify ethics/values issues that are related to the points the students raise in the discussion. Some questions that the teacher might ask to stimulate and direct this discussion are:

What do you think about the instructions your research group was given and did you have any reaction to the behavior of the other groups?
 

Did you have any problem with the way the bonus was awarded?
 

Which of the groups was instructed to behave in a manner that you think resembles the way real-world scientists behave?
 

What is your opinion about the roles of competition, collaboration and independent work in scientific research?
 

Are the standards of behavior that you expect of scientists any different than those you set for other professional workers?
 

When the continuation of this discussion no longer appears to be fruitful, the students should be shown the video The Race for the Double Helix. After viewing the video, the teacher should lead another discussion.(57) Some suggested questions for this second discussion are:


Instructions and Handouts for Students:

1. You will be assigned to a four-student "research group."
 

2. Your group will be given a sequence of nucleotide pairs carried by a piece of DNA. Using the left hand set of nucleotides as a template, and your knowledge of the base-pairing that occurs in RNA, transcribe the corresponding strand of mRNA.

3. As you have learned, each successive set of three mRNA nucleotides is a codon that codes for a particular amino acid. Using Table 1, determine the amino acid sequence that would be produced by the mRNA you transcribed.
 

4. Use table 2 to determine the sequence of characters (letters, spaces or punctuation marks) that correspond to your DNA sequence, and write them in the appropriate place on your data sheet.
 
 

Groups A, B and C:

5. Your group is collaborating with groups B and C (or A and C, or B and C). After deciphering the part of the message coded by your piece of DNA, you should share your results with these other two groups to complete missing sections of the message indicated by the numbers of spaces in parenthesis. You should then "publish" your results on the black board for the other groups to share. You may then try to complete any missing part of the message by guessing. When you think you have the entire correct message, report it to your teacher who will give a bonus to the first group that gets it right.
 

Groups D and E:

5. Your group is intent on being the first to decode the entire message. You find that After deciphering the part of the message coded by your piece of DNA, you are missing sections of the message indicated by the numbers of spaces in parenthesis. You should try to obtain the missing information from the other groups by any means you can devise, without sharing your results with them. When you think you have the entire correct message, report it to your teacher who will give a bonus to the first group that gets it right.
 

Group F.

5. Your group believes in methodical, independent work. You do not wish to publish your work until you are sure it is correct. Unfortunately, you find that after you decipher the message corresponding to your piece of DNA, it contains an error. You may try to independently deduce (guess) the correct complete message. Only if you are sure that you know what it is should you report it to your teacher who will give a bonus to the first group that gets it right.
 
 

DNA Pieces

(51 SPACES) (24 SPACES)     (18 SPACES)    
TA AT TA TA TA CG GC
AT CG AT TA GC TA TA
CG AT AT GC GC TA GC
CG TA TA AT GC GC  
TA GC TA GC CG TA  
TA GC TA AT GC TA  
GC CG AT TA AT TA  
TA TA TA AT TA TA  
CG GC TA GC GC CG  
AT CG AT AT TA GC  
TA TA TA TA AT CG  
GC AT GC GC CG AT  

Group B
(51 SPACES)     (36 SPACES)  
T A CG TA CG GC
AT CG TA GC CG
CG TA CG AT AT
CG TA AT CG AT
TA TA GC TA TA
TA CG AT TA GC
GC TA TA CG (27 SPACES)
TA AT AT TA  
CG AT GC GC  
AT AT AT GC  
TA TA TA TA  
GC AT GC TA  

Group C
(51 SPACES) (24 SPACES)     (18 SPACES)
TA AT TA TA TA
AT CG AT TA GC
CG AT AT GC GC
CG TA TA AT GC
TA GC TA GC CG
TA GC TA AT GC
GC CG AT TA AT
TA TA TA AT TA
CG GC TA GC GC
AT CG AT AT (18 SPACES)
TA TA TA TA  
GC AT GC GC  

Groups D and E
(51 SPACES)        
TA CG TA AT TA
AT CG TA CG AT
CG TA CG AT AT
CG TA AT TA TA
TA TA GC GC TA
TA CG AT GC TA
GC TA TA CG AT
TA AT AT TA TA
CG AT GC GC TA
AT AT AT CG AT
TA TA TA TA TA
GC AT GC AT GC
        (57 SPACES)

Group F
CG GC AT TA AT CG GC
AT AT TA TA TA TA CG
AT CG AT CG TA TA AT
CG CG CG AT TA CG AT
TA GC CG GC AT TA CG
TA TA TA AT TA GC CG
CG TA TA TA TA GC AT
TA GC GC AT AT TA CG
AT TA TA GC TA TA TA
GC GC CG AT GC CG AT
AT AT AT TA TA CG GC
AT CG TA GC TA AT TA
TA TA GC AT GC AT AT
TA CG CG CG AT TA  
TA CG CG AT GC GC  
CG TA TA TA AT TA  
CG GC TA GC TA GC  
AT GC TA GC AT GC  
TA CG CG CG GC GC  
TA GC TA TA AT CG  
AT GC AT GC TA GC  
GC TA AT CG GC AT  
TA AT AT TA CG TA  
CG AT TA AT GC GC  
GC TA AT TA AT CG  

The Amino Acids
Abbreviation Name Abbreviation Name
gly glycine ala alanine
val valine ile isoleucine
leu leucine ser serine
thr threonine pro proline
asp aspartate glu glutamate
lys lysine arg arginine
asn asparagine gln glutamine
cys cysteine met methionine
trp tryptophan phe phenylalanine
tyr tyrosine his histidine
term termination    

Table 1: The Genetic Code: Codons and the Amino Acids They Code
First Two Nucleotides of the Codon Last Nucleotide of the Codon
U C A G
UU phe phe leu leu
UC ser ser ser ser
UA tyr tyr term term
UG cys cys term ttrp
CU leu leu leu leu
CC pro pro pro pro
CA his his gln gln
CG arg arg arg arg
AU ile ile ile ile
AC thr thr thr thr
AA asn asn asn asn
AG ser ser arg arg
GU val val val val
GC ala ala ala ala
GA asp asp glu glu
GG gly gly gly gly

 
 

Table 2 Amino Acid to Character Conversion
Amino Acid Character Amino Acid Character Amino Acid Character
Glycine A Alanine B Valine C
Isoleucine E Leucine G Serine H
Threonine I Proline L Aspartate N
Glutamate O Lysine R Arginine S
Asparagine T Glutamine U Cysteine W
Methionine Y Tryptophan D Phenylalanine J
Tyrosine Space Histidine ! Termination .

 
 
 
 
 

RACE FOR THE DOUBLE HELIX -- DATA SHEET

Name ______________________ Group _____ Period _____ Teacher ____________________
DNA mRNA Amino Acid Character   DNA mRNA Amino Acid Character   DNA mRNA Amino Acid Character
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    
____ ____       ____ ____       ____ ____    
____ ____ _______ ______   ____ ____ _______ ______   ____ ____ _______ ______
____ ____       ____ ____       ____ ____    

 

Discussion:

Although this lesson requires a substantial investment of classroom time, teachers who have used it with properly prepared students commented that it serves to concretize the mechanism by which DNA codes for protein synthesis, while stimulating very rich and rewarding student discussions of important ethical issues related to the behavior of scientists.

In the discussions, it is important to direct attention to the significance and generality of the issues, rather than the particular circumstances of the student exercise, or the specific personality traits of the characters in the video. These general issues include the common conflict between a scientist's personal values, such as the desire to achieve success or fame, and the ethical demands of the scientific profession. Students should be challenged to consider why collaboration, sharing of information and the fair assignment of credit for discoveries are important to the advancement of scientific knowledge, but may often be compromised due to the fact that scientists are human beings with competing personal needs and desires. An effort should be made to take the discussion arising from the constraints imposed on women in science beyond the obvious negative aspects of overt sexism or racism. A possible way to do this is to ask students to consider whether the ranking of the importance of research problems by women or minority members might be significantly different from the choices made by relatively affluent white males.

For those teachers who can not devote four classroom periods to this lesson, the required time can be cut in half by eliminating either the viewing of the video and related discussion, or the DNA coding exercise. While this significantly reduces the student experience that can be used to probe the issues, teachers report that worthwhile ethic/values education is still achieved.

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