Multiple Choice
Which option correctly describes a key structural difference between DNA and RNA?
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7. DNA and Chromosome Structure
DNA Structure
Multiple Choice
In a DNA strand, how can you identify the 5' and 3' ends based on the chemical structure of the sugar-phosphate backbone?
A
The 5' end has a phosphate group attached to the 5' carbon of deoxyribose, while the 3' end has a free hydroxyl (3'-OH) group on the 3' carbon.
B
The 5' end is identified by the presence of a free nitrogenous base, while the 3' end is identified by the presence of hydrogen bonds to the complementary strand.
C
The 5' end always corresponds to the end of the strand with A–T base pairs, while the 3' end corresponds to the end with G–C base pairs.
D
The 5' end has a free hydroxyl (5'-OH) group on the 5' carbon, while the 3' end has a phosphate group attached to the 3' carbon.
Verified step by step guidance1
Understand that the DNA strand has a sugar-phosphate backbone made of deoxyribose sugars linked by phosphate groups.
Recall that each deoxyribose sugar has five carbon atoms numbered 1' through 5'. The numbering is crucial to identifying the ends of the strand.
The 5' end of the DNA strand is characterized by a phosphate group attached to the 5' carbon of the deoxyribose sugar. This phosphate is free and not linked to another nucleotide.
The 3' end of the DNA strand has a free hydroxyl group (-OH) attached to the 3' carbon of the deoxyribose sugar, which is not connected to another phosphate group.
Therefore, to identify the 5' and 3' ends, look for the free phosphate group on the 5' carbon for the 5' end, and the free hydroxyl group on the 3' carbon for the 3' end.
