sialic acid

(noun)

A derivative of neuraminic acid (a nine-carbon monosaccharide) that is often the sugar part of glycoproteins.

Examples of sialic acid in the following topics:

  • Attachment and Entry to the Host Cell

    • HA proteins bind to cells with sialic acid on the membranes, such as cells in the upper respiratory tract or erythrocytes.
    • First, it allows the recognition of target vertebrate cells, accomplished through the binding of these cells' sialic acid-containing receptors.
    • HA binds to the monosaccharide sialic acid that is present on the surface of its target cells, which causes the viral particles to stick to the cell's surface.

  • Replicative Cycle of Influenza A

    • Influenza viruses bind through hemagglutinin onto sialic acid sugars on the surfaces of epithelial cells, typically in the nose, throat, and lungs of mammals, and the intestines of birds (Step 1 in infection figure ).
    • It is known that virions converge to the microtubule organizing center, interact with acidic endosomes, and finally enter the target endosomes for genome release.
    • Once inside the cell, the acidic conditions in the endosome cause two events to happen:
    • As before, the viruses adhere to the cell through hemagglutinin; the mature viruses detach once their neuraminidase has cleaved sialic acid residues from the host cell.

  • Antiviral Agents that Prevent Virus Uncoating or Release

    • It cleaves sialic acid from glycoproteins on the surface of the host cell and allows the viral particles to leave the cell.

  • Polyprotic Acid Titrations

    • Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule.
    • Common examples of monoprotic acids in mineral acids include hydrochloric acid (HCl) and nitric acid (HNO3).
    • On the other hand, for organic acids the term mainly indicates the presence of one carboxylic acid group, and sometimes these acids are known as monocarboxylic acid.
    • Polyprotic acid are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule.
    • An example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid.

  • Diprotic and Polyprotic Acids

    • Diprotic and polyprotic acids contain multiple acidic protons that dissociate in distinct, sequential steps.
    • As their name suggests, polyprotic acids contain more than one acidic proton.
    • Two common examples are carbonic acid (H2CO3, which has two acidic protons and is therefore a diprotic acid) and phosphoric acid (H3PO4, which has three acidic protons and is therefore a triprotic acid).
    • With any polyprotic acid, the first amd most strongly acidic proton dissociates completely before the second-most acidic proton even begins to dissociate.
    • Identify the key features that distinguish polyprotic acids from monoprotic acids.

  • Acid Dissociation Constant (Ka)

    • The acid dissociation constant (Ka) is the measure of the strength of an acid in solution.
    • The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution.
    • Acid dissociation constants are most often associated with weak acids, or acids that do not completely dissociate in solution.
    • Acids with a pKa value of less than about -2 are said to be strong acids.
    • Acetic acid is a weak acid with an acid dissociation constant $K_a=1.8\times 10^{-5}$ .

  • Strong Acids

    • The strength of an acid refers to the ease with which the acid loses a proton.
    • where HA is a protonated acid, H+ is the free acidic proton, and A- is the conjugate base.
    • Strong acids yield weak conjugate bases.
    • For sulfuric acid, which is diprotic, the "strong acid" designation refers only to the dissociation of the first proton:
    • p-Toluenesulfonic acid is an example of an organic soluble strong acid, with a pKa of -2.8.

  • Weak Acids

    • The majority of acids are weak.
    • Examples of weak acids include acetic acid (CH3COOH), which is found in vinegar, and oxalic acid (H2C2O4), which is found in some vegetables.
    • Acids with a Ka less than 1.8×10−16 are weaker acids than water.
    • The Ka of acetic acid is $1.8\times 10^{-5}$.
    • Although it is only a weak acid, a concentrated enough solution of acetic acid can still be quite acidic.

  • The Brønsted-Lowry Definition of Acids and Bases

    • Originally, acids and bases were defined by Svante Arrhenius.
    • A wide range of compounds can be classified in the Brønsted-Lowry framework: mineral acids and derivatives such as sulfonates, carboxylic acids, amines, carbon acids, and many more.
    • The conjugate acid is the species that is formed when the Brønsted base accepts a proton from the Brønsted acid.
    • Here, acetic acid acts as a Brønsted-Lowry acid, donating a proton to water, which acts as the Brønsted-Lowry base.
    • Chemistry 12.1 What are Acids and Bases?

  • Oxoacids

    • Halogen oxoacids include hypochlorous acid (HOCl); chlorous acid(HOClO); chloric acid(HOClO2); oerchloric acid(HOClO3); oerbromic acid (HOBrO3)
    • Consider the simple oxyacids HOI (hypoiodous acid), HOBr (hypobromous acid), and HOCl (hypochlorous acid).
    • The strongest acid is perchloric acid on the left, and the weakest is hypochlorous acid on the far right.
    • Carboxylic acids are the most common type of organic acid.
    • Mellitic acid is an example of a hexacarboxylic acid.