Nucleotide Bases Each base has a slightly different shape Refer to by first letter of name (A,T,G,C) Chargaff’s Rules 1950’s – Biochemist Erwin Chargaff Found: Amount of Adenine always = Amount of Thymine Amount of Guanine always = Amount of Cytosine
DNA Structure Double Helix 2 sides of “ladder” = alternating sugar and phosphate The rungs of the ladder = pair of nucleotide bases A pairs with T G pairs with C How does this structure explain Chargoff’s findings?
Making Copies of DNA A pairs with T and G pairs with C therefore One side of DNA is complementary to the other. EX. A sequence ACCG always binds to TGGC. Allows for DNA to replicate.