A double stranded DNA strand contains 26 pyrimidines. How many purines will the copied strand contain?

Question

A.  0
B.  13
C.  26
D.  52

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

Gather Content
· What do you know about base pairing? How does it relate to the question?

Consider Possibilities  
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  26

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about base pairing between pyrimidines and purines.
· What type of thinking is required?
        o You are being asked to apply your knowledge of how pyrimidines and purines bind to each other in forming a double strand of DNA.
· What key words does the question contain and what do they mean?
        o Pyrimidines – the nucleotides cytosine and thymine.
        o Purines – the nucleotides adenine and guanine.

Gather Content
· What do you know about base pairing? How does it relate to the question?
        o Pyrimidines and purines on complementary strands of DNA through hydrogen bonding.  Thymine pairs with adenine and cytosine pairs with guanine.

Consider Possibilities  
· What other information is related to the question? Which information is most useful?
        o Because pyrimidines and purines form base pairs, for each pyrimidine there will be a purine.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o If there are 26 pyrimidines in a double strand of DNA, then there will be 26 purines.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to apply the structure of DNA to predict the number of purines if you know the number of pyrimidines. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall what pyrimidines and purines are?  Did you realize that the two form base pairs in DNA?