helical

(adjective)

In the shape of a helix, twist.

Related Terms

Examples of helical in the following topics:

  • Helical Motion

    • Helical motion results when the velocity vector is not perpendicular to the magnetic field vector.
    • This produces helical motion (i.e., spiral motion) rather than a circular motion.
    • Describe conditions that lead to the helical motion of a charged particle in the magnetic field

  • 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 simple figure eight is the simplest supercoil, and is the shape a circular DNA assumes to accommodate one too many or one too few helical twists.
    • For each additional helical twist being accommodated, the lobes will show one more rotation about their axis.
    • Extra helical twists are positive and lead to positive supercoiling, while subtractive twisting causes negative supercoiling.
    • Note that the helical nature of the DNA duplex is omitted for clarity.

  • Virus Classification

    • Capsids are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex .
    • For example, the tobacco mosaic virus has a naked helical capsid .
    • (a) Rabies virus has a single-stranded RNA (ssRNA) core and an enveloped helical capsid, whereas (b) variola virus, the causative agent of smallpox, has a double-stranded DNA (dsDNA) core and a complex capsid.
    • Viruses can also be classified by the design of their capsids which are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex.
    • 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.

  • MreB and Determinants of Cell Morphology

    • Prokaryotes carrying the mreB gene can also be helical in shape.
    • MreB has long been thought to form a helical filament underneath the cytoplasmic membrane.
    • Recent research shows that peptidoglycan precursors are inserted into cell wall following helical pattern which is dependent on MreB, and it's reported that MreB also promote the GT activity of PBPs.
    • RodZ co-localizes with MreB helices in a manner that is strictly dependent on its cytoplasmic region.

  • General Morphology

    • Helical - These viruses are composed of a single type of capsomer stacked around a central axis to form a helical structure, which may have a central cavity, or hollow tube.
    • Complex - These viruses possess a capsid that is neither purely helical nor purely icosahedral, and that may possess extra structures such as protein tails or a complex outer wall.

  • Muscularis

    • The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches.
    • The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch.

  • Complex and Asymmetrical Virus Particles

    • While some have symmetrical shapes, viruses with asymmetrical structures are referred to as "complex. " These viruses possess a capsid that is neither purely helical nor purely icosahedral, and may possess extra structures such as protein tails or a complex outer walls.
    • Some bacteriophages, such as Enterobacteria phage T4 , have a complex structure consisting of an icosahedral head bound to a helical tail, which may have a hexagonal base plate with protruding protein tail fibers.

  • Secondary & Tertiary Structure of Large Peptides and Proteins

    • However, this molecule prefers to assume a coiled helical conformation shown in the last three diagrams below.
    • Other structural features that define an alpha-helix are: the relative locations of the donor and acceptor atoms of the hydrogen bond, the number of amino acid units per helical turn and the distance the turn occupies along the helical axis.
    • Other common helical conformations are 310 and 4.416.
    • Consequently, the presence of a proline in a peptide chain introduces a bend or kink that disrupts helices or sheets.
    • The peptide chains are largely alpha-helices.

  • History of DNA Research

    • In 1948, Linus Pauling discovered that many proteins included helical shapes from X-ray patterns and from attempts to physically model the structures.
    • Even in the initial diffraction data from DNA produced by Maurice Wilkins, it was evident that the structure involved helices.
    • However, there remained questions of how many strands came together, whether this number was the same for every helix, whether the bases pointed toward the helical axis or away, and ultimately, what were the explicit angles and coordinates of all the bonds and atoms.
    • 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.

  • Nature of the Virion

    • Virions of most plant viruses are rod-shaped; the capsid is a naked cylinder (lacking a fatty membrane) within which lies a straight or helical rod of nucleic acid.