double-helix structure

(noun)

The structure formed by double-stranded molecules of nucleic acids such as DNA and RNA.

Related Terms

Examples of double-helix structure in the following topics:

  • The DNA Double Helix

    • The DNA double helix looks like a twisted staircase, with the sugar and phosphate backbone surrounding complementary nitrogen bases.
    • DNA has a double-helix structure, with sugar and phosphate on the outside of the helix, forming the sugar-phosphate backbone of the DNA.
    • During DNA replication, each strand is copied, resulting in a daughter DNA double helix containing one parental DNA strand and a newly synthesized strand.
    • Native DNA is an antiparallel double helix.
    • In a double stranded DNA molecule, the two strands run antiparallel to one another so that one strand runs 5′ to 3′ and the other 3′ to 5′.

  • The Secondary & Tertiary Structures of DNA

    • This pairing, which is shown in the first diagram below, explained Chargaff's findings beautifully, and led them to suggest a double helix structure for DNA.
    • Before viewing this double helix structure itself, it is instructive to examine the base pairing interactions in greater detail.
    • After many trials and modifications, Watson and Crick conceived an ingenious double helix model for the secondary structure of DNA.
    • Coiling these coupled strands then leads to a double helix structure, shown as cross-linked ribbons in part b of the diagram.
    • All these transformations disrupt base pairing at the site of the change, and this produces a structural deformation in the double helix..

  • History of DNA Research

    • He was not able to propose the correct structure, but the patterns showed that DNA had a regular structure.
    • In the 1950s, three groups made it their goal to determine the structure of DNA.
    • Using X-ray diffraction, as well as data from Rosalind Franklin and her information about base paris, Watson and Crick arrived at the first accurate model of DNA's molecular structure, a double helix, in 1953 .
    • In 1957, Crick laid out the " Central Dogma, " which explained the relationship between DNA, RNA, and proteins, and articulated the "sequence hypothesis. " A critical confirmation of the replication mechanism that was implied by the double-helical structure followed in 1958 in the form of the Meselson-Stahl experiment.
    • James Watson and Francis Crick are credited with the discovery of the double helix structure of DNA.

  • Discovery of DNA

    • Pauling had discovered the secondary structure of proteins using X-ray crystallography.
    • Chargaff's research would help the Watson and Crick laboratory team to deduce the double helical structure of DNA.
    • In Wilkins’ lab, researcher Rosalind Franklin used X-ray diffraction methods to understand the structure of DNA.
    • Scientist Rosalind Franklin discovered the X-ray diffraction pattern of DNA (pictured at right), which helped to elucidate its double helix structure.
    • Explain the sequence of events leading up to the discovery of the structure of DNA

  • The Structure and Sequence of DNA

    • DNA is a double helix of two anti-parallel, complementary strands having a phosphate-sugar backbone with nitrogenous bases stacked inside.
    • The nitrogenous base can be a purine such as adenine (A) and guanine (G), characterized by double-ring structures, or a pyrimidine such as cytosine (C) and thymine (T), characterized by single-ring structures.
    • The diameter of the DNA double helix is 2 nm and is uniform throughout.
    • Therefore, ten base pairs are present per turn of the helix.
    • DNA has (a) a double helix structure and (b) phosphodiester bonds.

  • Eukaryotic Chromosomal Structure and Compaction

    • In the first level of compaction, short stretches of the DNA double helix wrap around a core of eight histone proteins at regular intervals along the entire length of the chromosome .
    • A DNA molecule in this form is about seven times shorter than the double helix without the histones.
    • The beads are about 10 nm in diameter, in contrast with the 2-nm diameter of a DNA double helix.
    • Double-stranded DNA wraps around histone proteins to form nucleosomes that have the appearance of "beads on a string."

  • DNA Replication in Prokaryotes

    • As the DNA opens up, Y-shaped structures called replication forks are formed.
    • Single-strand binding proteins coat the strands of DNA near the replication fork to prevent the single-stranded DNA from winding back into a double helix.
    • As we know, the DNA double helix is anti-parallel; that is, one strand is in the 5' to 3' direction and the other is oriented in the 3' to 5' direction.
    • Topoisomerase prevents the over-winding of the DNA double helix ahead of the replication fork as the DNA is opening up; it does so by causing temporary nicks in the DNA helix and then resealing it.
    • Single-strand binding proteins bind to the single-stranded DNA to prevent the helix from re-forming.

  • Biology: DNA Structure and Replication

    • DNA is a large macromolecule that (in three-dimensional space) forms the shape of a double helix, as shown in .
    • The "backbone" of each helix is formed from alternating deoxyribose and phosphate subunits as illustrated in .

  • Supercoiling

    • In a "relaxed" double-helical segment of B-DNA, the two strands twist around the helical axis once every 10.4 to 10.5 base pairs of sequence.
    • The twist is the number of helical turns in the DNA and the writhe is the number of times the double helix crosses over on itself (these are the supercoils).
    • Supercoiled DNA forms two structures; a plectoneme or a toroid, or a combination of both.
    • A negatively supercoiled DNA molecule will produce either a one-start left-handed helix, the toroid, or a two-start right-handed helix with terminal loops, the plectoneme.
    • This is a supercoiled structure of circular DNA molecules with low writhe.

  • Virus Classification

    • This genetic material may be single- or double-stranded.
    • The type of genetic material (DNA or RNA) and its structure (single- or double-stranded, linear or circular, and segmented or non-segmented) are used to classify the virus core structures .
    • Transmission electron micrographs of various viruses show their structures.
    • The capsid of the (a) polio virus is naked icosahedral; (b) the Epstein-Barr virus capsid is enveloped icosahedral; (c) the mumps virus capsid is an enveloped helix; (d) the tobacco mosaic virus capsid is naked helical; and (e) the herpesvirus capsid is complex.
    • The type of genetic material (DNA or RNA) and its structure (single- or double-stranded, linear or circular, and segmented or non-segmented) are used to classify the virus core structures.