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sciftw eNotes educator| Certified Educator

Imagine an extension ladder going straight up.  It has long straight bars going up both sides.  In between those two bars are the ladder rungs that a person would step on.  Now in your imagination, twist the ladder.  It should resemble a sort of corkscrew shape.  That's what DNA looks like.  It looks like a twisted ladder.  

The official shape is called a double helix.  The upright sides of the DNA strand are composed of phosphates and 5 carbon sugar molecules.  They alternate as they go up.  Phosphate, sugar, phosphate, sugar, etc.  Connecting the two sides are the ladder rungs.  In DNA, the "ladder rungs" are made of nitrogen base pairs.  The four bases are adenine, thymine, cytosine, and guanine.  They are abbreviated A, T, C, G.  A's always pair with T's.  C's always pair with G's.  The base pairs attach to each other and to the 5 carbon sugar (never the phosphate). 

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