What forms the backbone of the DNA molecule?

Related questions

• Why is the number of chromosomes an organisms has an even number?
• Why are chromosomes important to heredity?
• Why is DNA called the blueprint of life?
• How do genes differ from chromosomes?
• How can chromosomes be damaged?
• How does DNA code for proteins?
• How are chromosomes related to chromatin?
• What is dna?
• How are alleles and traits related?
• What is chromatin?