alpha helix

(noun)

A secondary structure found in many proteins, where the amino acids are arranged in a coil, or helix, with almost no free space on the inside and all side chains being pointed towards the outside.

Related Terms

Examples of alpha helix in the following topics:

  • RNA Bacteriophages

    • They adopt a secondary structure consisting of a six-stranded beta sheet and an alpha helix.

  • Bovine Spongiform Encephalopathy

    • TSEs can arise in animals that carry an allele which causes previously normal protein molecules to contort by themselves from an alpha helix arrangement to a beta sheet, which is the disease-causing shape for the particular protein.

  • Supercoiling

    • The two lobes of the figure eight will appear rotated either clockwise or counterclockwise with respect to one another, depending on whether the helix is over or underwound.
    • 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).
    • 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.

  • T Cell Receptors

    • The antigen receptor of MHC-restricted CD4 helper T cells and CD8 cytolytic T cell is a heterodimer consisting of two transmembrane polypeptide chains, designated alpha and beta, covalently linked to each other by disulfide bonds.
    • Each alpha and beta chain consists of one variable domain (V), one constant domain (C), a hydrophobic transmembrane region, and a short cytoplasmic region .
    • The recognition of peptide-MHC complexes is mediated by CDRs formed by both the alpha and beta chains of the TCR.
    • T cell receptor consists of alpha and beta chains, a transmembrane domain, and a cytoplasmic region.

  • Epsilonproteobacteria

    • Helicobacter is a genus of Gram-negative bacteria possessing a characteristic helix shape.

  • Inhibiting Nucleic Acid Synthesis

    • The double helix is unwound and each strand acts as a template for the next strand.

  • Prokaryotic Transcription and Translation Are Coupled

    • Many of these transcription factors are homodimers containing helix-turn-helix DNA-binding motifs.

  • Hydrogen Oxidation

    • H. pylori's helix shape (from which the generic name is derived) is thought to have evolved to penetrate the mucoid lining of the stomach.
    • H. pylori's helix shape (from which the generic name is derived) is thought to have evolved to penetrate the mucoid lining of the stomach.

  • Repression of Anabolic Pathways

    • Enhancers are sites on the DNA helix that are bound to by activators in order to loop the DNA bringing a specific promoter to the initiation complex.
    • The C-terminal tetramerization helix is not shown.

  • The Reverse TCA Cycle

    • 5) succincyl CoA is converted to alpha-ketoglutarate via an alpha-ketoglutarate synthase (reduction of carbon dioxide occurs and oxidation of coenzyme A)
    • 6) alpha-ketoglutarate is converted to isocitrate (NAD(P)H/H+ and CO2 is broken down to NAD(P+)