The structure of DNA

DNA is an example of a macromolecule, i.e. a large molecule with a special shape, which is built up from many smaller parts called sub-units .
If you could magnify part of a nucleus, you would see the DNA molecule looking like a twisted rope ladder - a double helix.
The two strands forming the sides of the ladder give it a strong yet flexible structure, which does not vary along its length.
Stretched between these are the "rungs" of the ladder, the parts of the DNA molecule which vary, and so the differences carry genetic information. These parts are made up of sections called bases, which fit together in pairs. Single section of DNA The 4 bases (so called because on their own they react with acids) are also usually known by their initials, as shown alongside:
A (adenine), paired with T (thymine)
and C (cytosine) paired with G (guanine).

Since T pairs with A, and G with C, there are actually 4 different possibilities at any position on a strand. The sequence or order of these bases in DNA is used to store and pass on the genetic information, in a similar way to computer data on a disc or tape.

If one strand of DNA has the base sequence C A T G A G C G C G A T , what will be the sequence on the other strand? > GTA CTC GCG CTA