DNA, or deoxyribonucleic acid, is a vital component that encodes instructions for an organism's survival and fitness.
In order to understand the functions and processes DNA undergoes, it is important to know its structure.
DNA's basic structure is composed of two long strands intertwined with each other in a spiral staircase formation, called a double helix:
If we unwind the two strands, we can see that each strand is divided into units called nucleotides
Each nucleotide is composed of 3 main sections:
Phosphate group
Pentose sugar (5 carbon ring structure)
One of the 4 nitrogenous bases (either having 1 ring or two rings):
- Adenine (A)
- Thymine (T)
- Cytosine (C)
- Guanine (G)
Adenine and Guanine are considered as purines, with a double-ringed structure
Cytosine and Thymine are considered as pyrimidines, with a single-ringed structure
[A simple way of remember this is "purines are not pure, so you have to cut it off", making it the bigger, two-ringed structure]
-
Phosphodiester linkages link 5’ and 3’ ends of nucleotides together through a phosphate group (5’ and 3’ are specific carbon orientations on pentose sugar shown below):
Notice how each single strand goes from 5' to 3'. The importance of this will be discussed in my next blog about DNA replication.
--
Going back to nitrogenous bases (A,T,C,G), the nucleotide from one strand is always COMPLEMENTARY to the nucleotide on the other strand:
A is always paired with T and vise versa
G is always paired with C and vise versa
Notice how pyrimidines are always paired with purines:
--
Between each base pair, hydrogen bonds are formed to link them together.
In A-T pairing, 2 hydrogen bonds are formed. In G-C pairings, 3 hydrogen bonds are formed:
---
If you still have questions, I found this Youtube video very helpful:
Stay tuned for the next blog about DNA replication! ^_^
Comments