1. KEY CONCEPT DNA structure is the same in all organisms.

2. DNA is composed of four types of nucleotides.
DNA is made up of a long chain of nucleotides.
Each nucleotide has ________ parts.
_____________________
phosphate group
deoxyribose (sugar)
nitrogen-containing
base

3. The nitrogen containing bases are the only difference in the four nucleotides.

4. Watson and Crick determined the three-dimensional structure of DNA by building models.
They realized that DNA is a double helix that is made up of a ________-____________ backbone on the outside with _____ on the inside.

5. Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff.
Franklin’s x-ray images suggested that DNA was a _________ _________ of even width.
Chargaff’s rules stated that ____=____ and ____=____.

6. Nucleotides always pair in the same way.
The _______-________ rules show how nucleotides always pair up in DNA.
____ pairs with ____
____ pairs with ____
Because a pyrimidine (_______ ring) pairs with a purine (_________ ring), the helix has a uniform width. C G T A

7. The backbone is connected by _____________ bonds.
The bases are connected by _____________ bonds.
hydrogen bond
covalent bond