These bacteria change the nitrogen in the atmosphere into a form that we can use to make proteins

Cyanobacteria, Anabaena and Azotobactor are called Nitrogen fixing bacteria. These bacteria change the nitrogen in the atmosphere into a form that is used by the plants to make proteins. Plants take nitrogen in the form of nitrates. The atmospheric nitrogen is first converted into ammonia after that ammonia is converted into nitrates and this nitrates use by the plants to make proteins.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.