1. Biology 1-1a
DNA Structure

2. 1-1a: The Structure of DNA
DNA (deoxyribonucleic acid) is a polymer, a long, chainlike molecule made up of subunits called monomers.
Hint: “poly” means “many” and “mono” means “one”
In DNA, the monomers are called nucleotides

3. 1-1a: The Structure of DNA
When the monomers or nucleotides are linked together into a chain, they form a polymer or polynucleotide.
To form DNA, two of these polynucleotide chains wrap around each other to form a double helix.

4. 1-1a: The Structure of DNA
A closer look at nucleotides:
Each nucleotide is made up of 3 parts
A sugar
A phosphate group
A nitrogenous base
There are 4 types of bases: A,C,T,G

5. The Nitrogenous Bases

6. 1-1a: The Structure of DNA
The sugar and phosphate group form the “backbone” of the polynucleotide
When the nucleotides join together to form a polynucleotide, the order of the nitrogenous bases encodes the information.

7. Memory Aide:
Imagine that the nitrogenous bases are letters and when you put them into a particular order they form words.
These “words” or combinations of nitrogenous bases are what encodes the information contained within our DNA

8. 1-1a: The Structure of DNA
To complete the DNA molecule, two polynucleotide strands must bond together and twist up into a shape called a “double helix”
This occurs in a very specific way…

9. 1-1a: The Structure of DNA
First, the individual polynucleotide chains must be arranged so that their sugar-phosphate backbones are on the outside with the nitrogenous bases sticking inwards

10. 1-1a: The Structure of DNA
Next, the nitrogenous bases pair up in a very specific way:
A – T
C – G
An A will NEVER connect to a G, just as a C will NEVER connect to a T

11. 1-1a: The Structure of DNA
Once correctly paired, a special type of bond, called a hydrogen bond, forms to hold the paired nitrogenous bases together.

12. 1-1a: The Structure of DNA
Finally, the pairing of the nitrogenous bases causes the whole DNA structure to be twisted into a sort of twisted ladder shape called a double helix