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DNA is the molecule that holds all of the important information about an organism. It allows this information to be passed down from one generation to the next.
DNA is made of a double-stranded helix that holds together by weak hydrogen bonds between purine-pyrimidine nucleotide base pairs. Each pair consists of an adenine (A), thymine (T), cytosine (C), and guanine (G).
Double Helix
A DNA molecule is composed of two strands that wind around each other and form a double helix. Each strand is made up of a long linear chain of smaller units called nucleotides, which are joined by chemical bonds.
During the process of DNA replication, each strand is copied into a new double helix. This allows for the synthesis of proteins in the body.
The double helix is a twisting structure, with the backbone of sugar and phosphate molecules surrounding complementary nitrogen bases. It looks like a long ladder twisted into a helix, or coil.
In the 1950s, American biologist James Watson and British physicist Francis Crick proposed a model for the double helix. They used information from Rosalind Franklin’s X-ray diffraction study to confirm the structure of the DNA helix.
Base Pairs
Within each strand of DNA, two nitrogenous molecules called base pairs are chemically linked together by hydrogen bonds. These bonds hold the two strands of DNA together, making them possible to form double-stranded structures.
Specifically, these hydrogen-bonded base pairs are made up of adenine (A) and thymine (T) in DNA and guanine (G) and cytosine (C) in RNA. These bases bond with each other according to a set of universal rules known as base pairing.
In DNA, adenine always pairs with thymine and guanine always pairs with cytosine. In RNA, however, adenine is replaced by uracil (U) and thymine is substituted with cytosine.
The length of the DNA molecule is determined by these base pairs. Because of this, one human genome contains around 3 billion base pairs.
Hydrogen Bonds
Hydrogen bonds are electrostatic interactions between a hydrogen atom (H) and an atom or group of atoms that is more electronegative than H. The hydrogen atom donates electrons to the electronegative atom or group that accepts the bond, creating an attraction between the two.
These H-bonds are essential in the structures of DNA, proteins and other macromolecules that need to fold into a specific shape to accomplish their biological function. For example, the double helical structure of DNA is largely due to hydrogen bonding between base pairs that link one complementary strand to the other and enable replication.
In addition, hydrogen bonds between amino acid residues participating in the secondary structure of proteins form alpha and beta helixes. When the spacing between amino acid residues is regular, an alpha helix is formed; when there is less spacing between alternating amino acids, a beta sheet is formed.
Polynucleotide Chains
Deoxyribonucleic acid (DNA) is a polynucleotide chain of nucleotides that stores and transmits genetic information. Each molecule contains three parts: a nitrogenous base, a sugar molecule, and at least one phosphate group. Each sugar molecule is linked to its neighbors through a series of bonds called phosphodiester links.
DNA consists of two polynucleotide chains that are wound together in an antiparallel fashion to form a double helix. These helix strands are firmly held together by hydrogen bonds between the complementary bases on either strand.
The four nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine and guanine are purines, while cytosine and thymine are pyrimidine’s.