If there is 28% adenine, then there must be 28% cytosine for the DNA composition of a particular organism.

Question

Answer the following statement true (T) or false (F)

Answer 1

False

Clarify Question

What is the key concept addressed by the question?

     • The question is asking about complementary base pairing in a DNA molecule.

What type of thinking is required? 

     • You are being asked to take what you already know about complementary base pairing in a DNA molecule and to extend, or apply, the knowledge to determine the relative amount of nucleotides in a DNA sample.

What key words does this question contain and what do they mean?

     • DNA, a nucleic acid that functions as a double-stranded helix

     • Adenine, which is a nucleotide found in DNA; also known as A

     • Cytosine, which is a nucleotide found in DNA; also known as C

 
Gather Content

What do you know about DNA nucleotides and complementary base pairing?  How does it relate to the question?

     • What nucleotides are found in a DNA molecule? Which bases pair together? Which base pairs with A? Which base pairs with C? If 28% of the bases in a DNA molecule are A, what percent should be T? A and T together would comprise how much of the DNA molecule?

     • This question is providing you with some knowledge about the composition of a DNA molecule-28% of the molecule is adenine (A). Knowing the facts complementary base pairing will allow you to determine the percentage of the remaining bases and to determine if there is 28% C.

 
Consider Possibilities

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

     • If 28% of the DNA is composed of A, then you know 28% of the bases must be T, since A and T are complementary. What is 28% + 28%? How much DNA is unaccounted for if you know 56% of the bases are A and T? What bases are left to make up the rest (44%) of the DNA? What do you know about the remaining two bases, G and C? If G and C make up 44% of the DNA, how much of that DNA is G and how much is C?

 
Choose Answer 

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

     • The question is asking you to determine how much C is in a DNA sample. Remember that DNA is composed of four nucleotides, A, T, C, and G. You know the relative amount of A in the sample-28%. If 28% of the DNA is composed of A, then 28% must be T, since A and T are complementary bases. Together A + T equals 56%. This means that 44% of the DNA must be composed of the remaining two bases, G + C. G and C are complementary to each other, and so must be present in equal amounts. If G+C = 44%, and G=C, then how much C must be present in the sample? Is it 28%

 
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?

     • This question asked you about complementary base pairing. Answering this question correctly depended on your ability to understand base pairing rules and to extend, or apply, this knowledge to determine the base pair composition of a DNA sample.  

     • If you got the correct answer, great! Remember it's important to keep using an effective systematic approach to answering questions and to reinforce those good habits over time. If you got an incorrect answer, where did the process break down? Did you remember DNA is composed of four nucleotides (or bases) A, T, C, and G? Did you remember the base pairing rules, A pairs with T and G pairs with C? Did you understand that if you consider the amount of A + T + G + C in a DNA sample it must add up to 100%? Did you understand that in a DNA sample, the amount of G must equal the amount of C and the amount of A must equal the amount of T? Did you understand that if there is 28% A in a sample that there must be 28% T? Did you understand that the amount of A and T in the given sample was 56% and which meant that G and C must comprise the remaining 44%? Were you then able to extend this information, and conclude that G and C, being present in equal amounts, must each account for 22% of the bases in the DNA?