Objective: What is the structure of DNA?

Do Now: Take out your HW and notes

Watson and Crick- Modeled DNA’s structure.- Using Franklin’s work, created a new model in which two strands of

nucleotides wound about each other, forming a double helix

• Chargaff’s rules state that in any species there is an equal number of A and T bases, and an equal number of G and C bases

DNA (deoxyribonucleic acid)

The heritable genetic information of an organism

• Write down on your note sheet the importance of Watson and Crick.

What does DNA look like?

Double Helix: structure of DNA – 2 strands, twisted into a helical shape

Make an analogy for the structure of DNA.

Nucleotides• Subunits (monomers) of DNA (polymer)

Made up of:

1.Sugar

2.Phosphate group

3.Nitrogenous Base

Nucleotides join together• Joined together by covalent bonds that connect sugar of

one nucleotide to the phosphate group of the next• The repeating pattern of sugar-phosphate is called a

sugar-phosphate “backbone”

Base-Pair Rule

• DNA is made up of 4 nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

The Base Pairing Rule

(A) Adenine = (T) Thymine

(C) Cytosine = (G) Guanine

Bases joined together by hydrogen bonds

Fig. 16-UN1

Purine + purine: too wide

Pyrimidine + pyrimidine: too narrow

Purine + pyrimidine: width consistent with X-ray data

Fig. 16-8

Cytosine (C)

Adenine (A) Thymine (T)

Guanine (G)

Practice• One DNA strand is provided, write the

bases of the complimentary strandC

G

T

T

A

C

G

T

C

G

G

C

A

A

T

G

C

A

G

C

http://www.youtube.com/watch?v=qy8dk5iS1f0

Activity- Making a Model of DNA

• Materials:– 4 beads of different color– 2 long pipe cleaners– 8-12 short pieces of pipe cleaner– 1 index card– 1 DNA sequence