Double-Helix+and+base-pairing

Double helix refers to the structure of DNA . The structure of DNA  was first published in the journal Nature   by James D. Watson   and Francis Crick   in 1953, based upon data from Maurice Wilkins   and Rosalind Franklin  . Crick, Wilkins and Watson each received the Nobel Prize <span style="FONT-FAMILY: 'Times New Roman', Times, serif"> for their contributions to the discovery. Franklin died before her contribution could be acknowledged, and due to the fact that they cannot be awarded posthumously, never received a Nobel Prize. <span style="FONT-FAMILY: 'Times New Roman', Times, serif">The DNA double helix is a right-handed spiral polymer of <span style="FONT-FAMILY: 'Times New Roman', Times, serif">nucleic acids <span style="FONT-FAMILY: 'Times New Roman', Times, serif">, held together by <span style="FONT-FAMILY: 'Times New Roman', Times, serif">nucleotides  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"> which <span style="FONT-FAMILY: 'Times New Roman', Times, serif">base pair  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"> together. A single turn of the helix constitutes ten nucleotides. The double helix structure of DNA contains a <span style="FONT-FAMILY: 'Times New Roman', Times, serif">major groove <span style="FONT-FAMILY: 'Times New Roman', Times, serif"> and <span style="FONT-FAMILY: 'Times New Roman', Times, serif">minor groove  <span style="FONT-FAMILY: 'Times New Roman', Times, serif">, the major groove being wider than the minor groove. Given the difference in widths of the major groove and minor groove, many proteins which bind to DNA do so through the wider major groove.The order, or <span style="FONT-FAMILY: 'Times New Roman', Times, serif">sequence <span style="FONT-FAMILY: 'Times New Roman', Times, serif">, of the nucleotides in the double helix within a <span style="FONT-FAMILY: 'Times New Roman', Times, serif">gene  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"> specifies the <span style="FONT-FAMILY: 'Times New Roman', Times, serif">primary structure  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"> of a <span style="FONT-FAMILY: 'Times New Roman', Times, serif">protein  <span style="FONT-FAMILY: 'Times New Roman', Times, serif">. <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">Base Pairing in  molecular biology , two  nucleotides  on opposite  complementary    DNA  or  RNA  strands that are connected via  hydrogen bonds  are called a **base pair** (often abbreviated bp). In the canonical //Watson-Crick base pairing//, adenine  (A) forms a base pair with  thymine  (T), as does  guanine  (G) with  cytosine  (C) in DNA. In RNA, thymine  is replaced by  uracil  (U). Non-Watson-Crick base pairing with alternate hydrogen bonding patterns also occur, especially in RNA; common such patterns are Hoogsteen base pairs. Pairing is also the mechanism by which codons  on  messenger RNA  molecules are recognized by  anticodons  on  transfer RNA  during protein  translation. Some DNA- or RNA-binding enzymes can recognize specific base pairing patterns that identify particular regulatory regions of genes. <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">The size of an individual  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">gene    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"> or an organism's entire   <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">genome    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"> is often measured in base pairs because DNA is usually double-stranded. Hence, the number of total base pairs is equal to the number of  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">nucleotides    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"> in one of the strands (with the exception of non-coding single-stranded regions of   <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">telomeres    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">). The  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">haploid    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">   <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">human genome    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"> (23   <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">chromosomes    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">) is estimated to be about 3 billion base pairs long and to contain 20,000-25,000 distinct genes. <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">A **Kilobase** is a unit of measurement in  <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">molecular biology    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"> denoting 1000 base pairs of   <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">DNA    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"> or   <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">RNA    <span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">.

<span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif"><span style="FONT-FAMILY: 'Times New Roman', Times, serif">* Source: Wikipedia