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DNA Structure and Base Pairing

DNA, or deoxyribonucleic acid, is the molecular blueprint of life. It carries the genetic instructions used in the development, functioning, growth, and reproduction of all known living organisms. DNA is composed of two long strands that form a double helix, a structure that allows for the stable storage and accurate replication of genetic information. The sequence of nucleotide bases—adenine (A), thymine (T), cytosine (C), and guanine (G)—along these strands encodes the information necessary to build and maintain an organism. Understanding DNA structure and base pairing is essential to grasping how genetic information is passed from one generation to the next and how it influences traits and health.

Figures (6)

Chemical structure of DNA
Nucleic acid design can be used to create nucleic acid complexes with complicated secondary structures such as this four-arm junction. These four strands associate into this structure because it maximizes the number of correct base pairs, with As matched to Ts and Cs matched to Gs. Image from Mao, 2004.[5]
DNA structure and bases
The image above contains clickable links Interactive image of nucleic acid structure (primary, secondary, tertiary, and quaternary) using DNA helices and examples from the VS ribozyme and telomerase and nucleosome. (PDB: ADNA, 1BNA, 4OCB, 4R4V, 1YMO, 1EQZ​)
An example of RNA secondary structure. This image includes several structural elements, including; single-stranded and double-stranded areas, bulges, internal loops and hairpin loops. Double-stranded RNA forms an A-type helical structure, unlike the common B-type conformation taken by double-stranded DNA molecules.
A-B-Z-DNA Side View

DNA is a molecule that holds the instructions for building and maintaining living things. It looks like a twisted ladder, called a double helix, made of two long strands. Each rung of the ladder is made of pairs of four building blocks: adenine (A), thymine (T), cytosine (C), and guanine (G).

A always pairs with T, and C always pairs with G. This matching is called base pairing. The order of these bases along the DNA strands spells out the genetic code.

DNA is found in the nucleus of cells and is organized into structures called chromosomes. When a cell divides, DNA is copied so each new cell gets a full set of instructions. Understanding DNA helps explain how traits are passed from parents to offspring and how changes in DNA can affect health and development.

Key Points

  • A nucleotide is a building block of DNA that contains one base, one phosphate molecule, and the sugar molecule deoxyribose.
  • The phosphate backbone is the structure formed by the sugar and phosphate molecules in DNA, which form the two long, twisted chains of DNA.
  • Adenine is one of the four bases in DNA nucleotides, which pair with thymine in the complementary strands of DNA.
  • Thymine is one of the four bases in DNA nucleotides, which pair with adenine in the complementary strands of DNA.
  • Cytosine is one of the four bases in DNA nucleotides, which pair with guanine in the complementary strands of DNA.

Terms

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