If a short sequence of DNA is 5' AATTGCCGT 3', its complement is

Question

A.  5' AAAACGCCA 3'.
B.  3' TTAACGGCT 5'.
C.  3' TTAACGGCA 5'.
D.  3' TTAAGCCGA 5'.
E.  5' TTAACGGCA 3'.

Clarify Question
· What is the key concept addressed by the question?    
· What type of thinking is required?
  · What key words does the question contain?

  Gather Content
· What do you already know about base-pairing?

  Consider Possibilities
· Consider the different answer options. Which can you rule out?

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.  3' TTAACGGCA 5'.

Clarify Question
· What is the key concept addressed by the question?    o This question addresses base-pairing.
· What type of thinking is required?
    o Although you may not have seen this example before, you know enough about the concept to Apply your knowledge and understanding to this unfamiliar situation.
  · What key words does the question contain?
    o A DNA sequence has a direction, which is referred to as 5’ to 3’, or 3’ to 5’. These refer to the carbons on the sugar molecule which connect between the phosphates in the backbone. The complement of a DNA sequence is the sequence of its opposite strand.

  Gather Content
· What do you already know about base-pairing?
    o Base-pairing is the interaction that connects the two strands of a DNA molecule.
    o A pairs with T, and G pairs with C.

  Consider Possibilities
· Consider the different answer options. Which can you rule out?
    o We have learned that the DNA strands are antiparallel. That means that one strand runs 5’ to 3’, and the other runs 3’ to 5’.
    o One of the answers appears to base-pair properly, but would not be antiparallel, so you can rule that out.

Choose Answer   · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
    o Starting at the 5’ of the original sequence, we can deduce the complementary sequence.
    o The original strand starts with 5’, so it’s complement begins at the 3’ end.
    o The original strand starts out 5’ AATT.
    o We know that A base pairs with T, and vice versa, so its complement is 3’ TTAA.
    o We know that G base pairs with C, and vice versa, so continuing on the complete complement is: 3' TTAACGGCA 5'.

  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 required you to Apply your knowledge and understanding to this unfamiliar situation.
    o Did you remember that A binds with T, and G binds with C?     o Did you recognize that the two DNA strands are antiparallel, so the answer should begin 3’ TTAA?
    o Note: It is permissible to write a DNA strand in either direction. So an acceptable answer could also have been 5’ ACGGCAATT 3’. How is this different from the wrong answer 5’ TTAACGGCA 3’?