envelope

(noun)

an enclosing structure or cover, such as a membrane

Related Terms

Examples of envelope in the following topics:

  • Viral Morphology

    • Enveloped viruses have membranes surrounding capsids.
    • Animal viruses, such as HIV, are frequently enveloped.
    • Enveloped virions like HIV consist of nucleic acid and capsid proteins surrounded by a phospholipid bilayer envelope and its associated proteins.
    • Other envelope proteins include the matrix proteins that stabilize the envelope and often play a role in the assembly of progeny virions.
    • Because of the fragility of the envelope, non-enveloped viruses are more resistant to changes in temperature, pH, and some disinfectants than are enveloped viruses.

  • Virus Classification

    • Viruses are classified by factors such as their core content, capsid structure, presence of outer envelope, and how mRNA is produced.
    • Enveloped viruses have membranes surrounding capsids.
    • Animal viruses, such as HIV, are frequently enveloped.
    • Capsids are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex .
    • 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.

  • Animal Viruses

    • Non-enveloped or "naked" animal viruses may enter cells in two different ways.
    • Enveloped viruses also have two ways of entering cells after binding to their receptors: receptor-mediated endocytosis and fusion.
    • Many enveloped viruses enter the cell by receptor-mediated endocytosis in a fashion similar to some non-enveloped viruses.
    • On the other hand, fusion only occurs with enveloped virions.
    • These viruses, which include HIV among others, use special fusion proteins in their envelopes to cause the envelope to fuse with the plasma membrane of the cell, thus releasing the genome and capsid of the virus into the cell cytoplasm.

  • Meiosis II

    • If nuclear envelopes were formed, they fragment into vesicles.
    • The nuclear envelopes are completely broken down and the spindle is fully formed.
    • Nuclear envelopes form around the chromosomes.

  • Exocytosis

    • In exocytosis, waste material is enveloped in a membrane and fuses with the interior of the plasma membrane.
    • This fusion opens the membranous envelope on the exterior of the cell and the waste material is expelled into the extracellular space .

  • Vaccines and Anti-Viral Drugs for Treatment

    • Drugs have been developed that inhibit the fusion of the HIV viral envelope with the plasma membrane of the host cell (fusion inhibitors), the conversion of its RNA genome into double-stranded DNA (reverse transcriptase inhibitors), the integration of the viral DNA into the host genome (integrase inhibitors), and the processing of viral proteins (protease inhibitors).
    • (a) Tamiflu inhibits a viral enzyme called neuraminidase (NA) found in the influenza viral envelope.
    • (b) Neuraminidase cleaves the connection between viral hemagglutinin (HA), also found in the viral envelope, and glycoproteins on the host cell surface.
    • HIV, an enveloped, icosahedral virus, attaches to the CD4 receptor of an immune cell and fuses with the cell membrane.

  • Basic Structures of Prokaryotic Cells

    • Gram-negative bacteria have a relatively thin cell wall composed of a few layers of peptidoglycan (only 10 percent of the total cell wall), surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins.
    • This outer envelope is sometimes referred to as a second lipid bilayer.
    • The chemistry of this outer envelope is very different, however, from that of the typical lipid bilayer that forms plasma membranes.

  • Characteristics of Eukaryotic Cells

    • The nuclear envelope is a double-membrane structure that constitutes the outermost portion of the nucleus.
    • Both the inner and outer membranes of the nuclear envelope are phospholipid bilayers.
    • The nuclear envelope is punctuated with pores that control the passage of ions, molecules, and RNA between the nucleoplasm and cytoplasm.

  • Steps of Virus Infections

    • A virus attaches to a specific receptor site on the host cell membrane through attachment proteins in the capsid or via glycoproteins embedded in the viral envelope.
    • Some enveloped viruses enter the cell when the viral envelope fuses directly with the cell membrane.

  • The Mitotic Phase and the G0 Phase

    • During prophase, the "first phase," the nuclear envelope starts to dissociate into small vesicles.
    • The remnants of the nuclear envelope fragment.
    • Nuclear envelopes form around the chromosomes and nucleosomes appear within the nuclear area.