Concept 19 The DNA molecule is shaped like a twisted ladder.

HI! The discovery of the structure of DNA was a landmark in molecular biology research. Which of the following is a correct representation of DNA? (No, This is a left handed double helix.) (That is correct) (No, This is not the DNA double helix.) (No, The DNA helix does not have evenly spaced coils.) DNA is a right-handed double helix. If you curl the fingers of your right hand in the direction of the helical twists, your thumb will point upwards. This section of DNA has a sequence of nucleotides like this: CCGTATACAT Reading left to right, what is the nucleotide sequence on the other strand of DNA in this section? CCGTATACAT (No, this is not the complementary sequence.) TACATATGCC (No, this is the reverse sequence, not the complement.) AATGCGCACG (No, A does not pair with C and T does not pair with G.) GGCATATGTA (That is correct) Nucleotides base pair through hydrogen bonds; A pairs with T, and G pairs with C. In a DNA helix, the nucleotides of one strand are the complement of the nucleotides on the other strand. If the direction of the sugar-phosphate backbone of the bottom strand is 5�€™ to 3�€™ from left to right, what is the direction of the top strand from left to right? 5�€™ to 3�€™ (No, the DNA strands in a helix are anti-parallel. 3�€™ to 5�€™ (That is correct.) 3�€™ to 3�€™ (No, the sugar-phosphate backbone of DNA is not 3�€™ to 3�€™.) 5�€™ to 5�€™ (No, the sugar-phosphate backbone of DNA is not 5�€™ to 5�€™.) The sugar-phosphate backbone of DNA has the phosphate on the 5�€™ carbon linked to the 3�€™ carbon of the next sugar. Since DNA strands of the helix run anti-parallel, the direction of the top strand will be 3�€™ to 5�€™. CONGRATULATIONS!!! YOU'RE SO SMART!