Macromolecules: DNA Structure

 

 

1.  For this assignment, use the following simple shapes to represent the parts of a nucleotide:

 

 

                           = phosphate group                = deoxyribose                       = purine

 

                                                                                                                              = pyrimidine

 

(The pyrimidine should be noticeably smaller than a purine).

 

Draw the four different nucleotides found in DNA. Label each, and write the appropriate letters (A, T, G, or C in the squares or triangles:

 

 

 

 

 

 

 

 

 

 

 

 

 

2.    Now create a single strand of DNA three nucleotides long, consisting of one pyrimidine and two purines, linked by phosphodiester bonds. Identify the 5' end and 3’ end.   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.    Write down the sequence of your DNA strand in the 5' to 3' direction. For example, 5'–T–C–G–3' (note, this sequence doesn’t have the right combination of purines and pyrimidines).

 

 

 

Now write down the sequence that the complementary strand would have:

 

 

 

 

4.    Now using draw how the two complementary strands would be paired together to form a double stranded DNA molecule:

 

 

                                                                   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5.    Consider the relative sizes of purines vs. pyrimidines and the base-pairing rules. What implications does this have for the width of a double helix? What would happen if a mismatch occurred (i.e., a purine bonded with another purine?)