The backbone is sugar and phosphate
- The idea
- Predict
- See it
- Why
- Check
The idea
“The bases are bonded to each other in a line, and that chain holds the strand together.”
A, T, G and C spell out the code, so it's easy to picture them linked in a row. They actually hang off a chain of sugars and phosphates.
The short version
The mistake: The bases are bonded to each other in a line, and that chain holds the strand together.
What's actually true: Covalent bonds link each sugar to the next through a phosphate. That backbone holds the strand, and the bases hang off it.
- A nucleotide is a phosphate, a five-carbon sugar and a nitrogenous base on that sugar. The sugar is deoxyribose in DNA and ribose in RNA.
- The phosphate on one sugar's 5' carbon bonds to the 3' hydroxyl of the sugar before it. This phosphodiester linkage forms by dehydration synthesis.
- Bases stick out to the side. In a double helix they hydrogen-bond to bases on the other strand. Neighboring bases on one strand aren't covalently bonded.
- The backbone is the same in every nucleotide, so any base can follow any other. That's how base order carries information.
On the exam: The chain runs sugar, phosphate, sugar, phosphate. Bases hang off it, so losing one doesn't break the strand.