Overview of DNA Structure
DNA, or deoxyribonucleic acid, has a double helix structure resembling a twisted ladder. Discovered by James Watson and Francis Crick in 1953, it consists of two long strands coiled around each other. Each strand is made of nucleotides, which include a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G). The strands are held together by hydrogen bonds between complementary bases: A pairs with T, and C pairs with G.
Key Components of DNA
The backbone of each DNA strand is formed by alternating sugar and phosphate molecules, creating a strong skeletal structure. The bases project inward from this backbone, forming the rungs of the ladder through base pairing. The double helix is right-handed, with a diameter of about 2 nanometers and a full twist every 10 base pairs. The strands run in opposite directions, known as antiparallel orientation, which is essential for DNA replication and function.
Practical Example: DNA in Chromosomes
In human cells, DNA is packaged into chromosomes within the nucleus. For instance, the DNA in a single chromosome can be over 2 meters long when uncoiled but is tightly wound to fit inside the cell. During cell division, the double helix unwinds, allowing each strand to serve as a template for copying the genetic information, ensuring identical DNA is passed to daughter cells.
Importance and Applications of DNA Structure
The structure of DNA explains how genetic information is stored, replicated, and transmitted across generations, forming the basis of heredity. This knowledge has revolutionized fields like medicine, enabling applications such as genetic testing, gene therapy, and forensic science. Understanding base pairing also underpins biotechnology techniques like PCR for amplifying DNA segments.