Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning and reproduction of all known organisms and many viruses. DNA and ribonucleic acid are nucleic acids; the two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases, a sugar called deoxyribose, a phosphate group; the nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA; the complementary nitrogenous bases are divided into two groups and purines. In DNA, the pyrimidines are cytosine. Both strands of double-stranded DNA store the same biological information.
This information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences; the two strands of DNA are thus antiparallel. Attached to each sugar is one of four types of nucleobases, it is the sequence of these four nucleobases along the backbone. RNA strands are created using DNA strands as a template in a process called transcription, where DNA bases are exchanged for their corresponding bases except in the case of thymine, which RNA substitutes for uracil. Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms store most of their DNA inside the cell nucleus as nuclear DNA, some in the mitochondria as mitochondrial DNA or in chloroplasts as chloroplast DNA.
In contrast, prokaryotes store their DNA only in circular chromosomes. Within eukaryotic chromosomes, chromatin proteins, such as histones and organize DNA; these compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869, its molecular structure was first identified by Francis Crick and James Watson at the Cavendish Laboratory within the University of Cambridge in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling, a post-graduate student of Rosalind Franklin at King's College London. DNA is used by researchers as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity; the unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials.
DNA is a long polymer made from repeating units called nucleotides, each of, symbolized by a single letter: either A, T, C, or G. The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds. Both chains are coiled around the same axis, have the same pitch of 34 angstroms; the pair of chains has a radius of 10 angstroms. According to another study, when measured in a different solution, the DNA chain measured 22 to 26 angstroms wide, one nucleotide unit measured 3.3 Å long. Although each individual nucleotide is small, a DNA polymer can be large and contain hundreds of millions, such as in chromosome 1. Chromosome 1 is the largest human chromosome with 220 million base pairs, would be 85 mm long if straightened. DNA does not exist as a single strand, but instead as a pair of strands that are held together; these two long strands coil in the shape of a double helix.
The nucleotide contains both a segment of the backbone of a nucleobase. A nucleobase linked to a sugar is called a nucleoside, a base linked to a sugar and to one or more phosphate groups is called a nucleotide. A biopolymer comprising multiple linked nucleotides is called a polynucleotide; the backbone of the DNA strand is made from alternating sugar groups. The sugar in DNA is 2-deoxyribose, a pentose sugar; the sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These are known as the 3′-end, 5′-end carbons, the prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond. Therefore, any DNA strand has one end at which t
Heather Jenner was a matchmaker, who ran a marriage bureau, called "The Marriage Bureau", in Bond Street, London. The daughter of Cyril Arthur Lyon, an Army general, she married firstly, in 1942, Michael George Cox, in 1955, the writer Stephen Potter. Widowed in 1969, she married Sir John Hastings James, deputy master and Comptroller of the Royal Mint, she established the agency in 1939, after her own divorce, kept the business secret from her family and friends, using the name'Heather Jenner', as such activity was considered scandalous at the time. Her autobiography, Marriage is My Business, was published in 1954, she appeared as a "castaway" on the BBC Radio programme Desert Island Discs on 31 July 1967. ——. Un mariage par jour. Pierre Horay. ——. Marriage is My Business. Kimber. ——. The marriage book. Gerald Duckworth & Co Ltd. ——. Royal Wives. Gerald Duckworth & Co Ltd. ISBN 978-0715602881. ——. Men and Marriage. Michael Joseph. ISBN 978-0718103675. ——. Marriages are Made in Heaven. David & Charles. ISBN 978-0715376621
If glands are categorized by shape, alveolar glands contrast with tubular glands. Alveolar glands have a saclike secretory portion, are termed saccular glands, they have an enlarged lumen, hence the name similar to alveoli, the small air sacs in the lungs. Some sources draw a clear distinction between acinar and alveolar glands, based upon the size of the lumen. A further complication in the case of the alveolar glands may occur in the form of still smaller saccular diverticuli growing out from the main sacculi; the term "racemose gland" is used to describe a "compound alveolar gland" or "compound acinar gland."Branched alveolar glands are classified as follows: Acinus