DNA has a double-helix shape, like a ladder twisted into a spiral. Each step of the ladder is a pair of nucleotides.
Nucleotides
A nucleotide is a molecule made up of
- deoxyribose - a sugar with 5 carbon atoms
- a phosphate group - made of phosphorus and oxygen
- a nitrogenous base.
DNA is made up of four types of nucleotide
- Adenine (A)
- Thymine (T)
- Cytosine (C)
- Guanine (G)
Rungs of the ladder!
- The 'rungs' of the DNA ladder are made of two bases.
- One base coming from each side.
- Bases are held together by hydrogen bonds.
- The different bases are very specific - they are complementary and come in fixed pairs:
- adenine and thymine pair up (in 2 hydrogen bonds)
- cytosine and guanine pair up (in 3 hydrogen bonds)
- DNA can write 'codes' out of the 'letters' that are the bases.