Nucleotides, Base Pairing, and Structure of DNA

The Structure of DNA

• $Deoxyribonucleic Acid$ (DNA) $forms the shape of a double helix$, which is two strands that are twisted and wrapped around each other. The two strands of DNA run antiparallel, or in opposite directions, to each other. $One end is known as the 3’ end and the other end is known as the 5’ end.$
• The $backbone$ of the strands is made of a $sugar-phosphate group$. The sugar in this group is known as deoxyribose, the namesake of DNA, which is $made of carbon$. Carbon is an important element found in all organic, carbon-based, molecules.
• $The sugar-phosphate backbone attaches to one of the four nitrogenous bases found in DNA: adenine, guanine, thymine, and cytosine.$
• The nucleotides in DNA are hel$d together with hydrogen bonds$. These bonds are strong enough to hold the two pieces together, but the bonds are easy enough to break when the strands need to unravel for reproduction.
• In DNA, adenine always pairs with thymine; guanine always pairs with cytosine. Adenine and guanine are known as purines and have $two carbon rings in their structure$. Cytosine and thymine are known as pyrimidines and have $only one ring in their structure$. The two-ring compounds cannot bond together in DNA because that would make the DNA molecule too wide.
• The one-ring compounds cannot bond together in DNA because that would make the DNA molecule too small.
• $Erwin Chargaff$ found something interesting about DNA. Whenever he analyzed the composition of DNA, he always found that there was the same amount of thymine and adenine AND the same amount of cytosine and guanine. He called this Chargaff’s Rule.
• $Watson and Crick knew that DNA was the shape of a helix based on Rosalind Franklin’s work with x-ray crystallography and were the first scientists to build a model of the shape of DNA.$

Edited: 01 December 2022