DNA Structure3 Parts of a nucleotide:

•Nitrogenous Base

•Sugar

(Deoxyribose)

•Phosphate

There are 4 nitrogenous bases in DNA

• Adenine (A)

• Thymine (T)

• Guanine (G)

• Cytosine (C)

A&G=Purines T&C=Pyrimidines

Organism A T G CHuman 30.9 29.4 19.9 19.8Chicken 28.8 29.2 20.5 21.5Grasshopper 29.3 29.3 20.5 21.5Sea Urchin 32.8 32.1 17.7 17.3Wheat 27.3 27.1 22.7 22.8Yeast 31.3 32.9 18.7 17.1E. coli 24.7 23.6 26 25.7

Relative Proportions (%) of Bases in DNA

Chargaff’s Rules of DNA Base Pairing

1. Adenine only pairs with Thymine

2. Guanine only pairs with Cytosine

A-T and G-C

3. The the amount of Adenine (A) in an organism is equal to the amount of Thymine (T) in the organism.

4. The amount of Guanine (G) in an organism is equal to the amount of Cytosine (C) in the organism.

Chargaff’s Rules of DNA Base Pairing

A=T G=C

Practice:What would the complementary strand look like?

A T G G C C T G A A T A G C A C C

T AC C GG A C T T A T C G T G G

Cards Ready!

1. Which of the following does a nucleotide not contain?

A. Phosphate

B. Sugar

C. Fatty Acid

D. Both A&B

Question 2

What is the name of the bond that keeps both bases together?

A. Oxygen Bond

B. Strong Bond

C. Helium Bond

D. Hydrogen Bond

Question 3

Adenine would bond with which other base?

A. Guanine

B. Cytosine

C. Thymine

D. Adenine

Question 4

Guanine would bond with which other base?

A. Guanine

B. Cytosine

C. Thymine

D. Adenine

Question 5

Which of the following is not a part of Chargaffs rule?

A. A to T

B. C to G

C. The percentages/amount of nitrogenous bases are unequal.

D. The percentages/amount of nitrogenous bases are equal.