plasma membrane

Examples of plasma membrane in the following topics:

• Injuring the Plasma Membrane

  • Several types of antimicrobial drugs function by disrupting or injuring the plasma membrane.
  • The plasma membrane or cell membrane is a biological membrane that separates the interior of all cells from the outside environment.
  • The plasma membrane is selectively permeable to ions and organic molecules.
  • Diagram of a typical gram-negative bacterium, with the thin cell wall sandwiched between the red outer membrane and the thin green plasma membrane.
  • Discuss the function of the plasma membrane and how antimicrobial drugs target it

• Group Translocation

  • Bacteria may have a single plasma membrane (Gram-positive bacteria) or an inner membrane plus an outer membrane separated by the periplasm (Gram-negative bacteria).
  • Proteins may be incorporated into the plasma membrane.
  • The basic mechanism at the plasma membrane is similar to the eukaryotic one.
  • In most Gram-positive bacteria, certain proteins are targeted for export across the plasma membrane and subsequent covalent attachment to the bacterial cell wall.
  • It is known as a multi-component system that always involves enzymes of the plasma membrane and those in the cytoplasm.

• Gram-Negative Outer Membrane

  • The Gram-negative cell wall is composed of an outer membrane, a peptidoglygan layer, and a periplasm.
  • In the Gram-negative Bacteria the cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane.
  • In Gram-negative bacteria the outer membrane is usually thought of as part of the outer leaflet of the membrane structure and is relatively permeable.
  • Sandwiched between the outer membrane and the plasma membrane, a concentrated gel-like matrix (the periplasm) is found in the periplasmic space.
  • Together, the plasma membrane and the cell wall (outer membrane, peptidoglycan layer, and periplasm) constitute the gram-negative envelope.

• Sodium Pumps as an Alternative to Proton Pumps

  • Na+/K+-ATPase (Sodium-potassium adenosine triphosphatase, also known as Na+/K+ pump, sodium-potassium pump, or sodium pump) is an antiporter enzyme (EC 3.6.3.9) (an electrogenic transmembrane ATPase) located in the plasma membrane of all animal cells.
  • The mechanism responsible for this is the sodium-potassium pump, which moves these two ions in opposite directions across the plasma membrane.
  • This was investigated by following the passage of radioactively labeled ions across the plasma membrane of certain cells.
  • As in the H+ cycle, a fully operational Na+ cycle would include a primary Na+ pump that directly couples Na+ translocation to a chemical reaction, an Na+-transporting membrane ATP synthetase, a number of Na+-dependent membrane transporters, and an Na+-dependent flagellar motor.
  • First, Na+-based membrane energetics could improve the versatility of a pathogen by providing it with additional means of ATP synthesis, motility and solute uptake.

• Gram-Positive Cell Envelope

  • They lack the outer membrane envelope found in Gram-negative bacteria.
  • The teichoic acid polymers are occasionally anchored to the plasma membrane (called lipoteichoic acid, LTA), and apparently directed outward at right angles to the layers of peptidoglycan.
  • Another theory is that teichoic acids are in some way involved in the regulation and assembly of muramic acid sub-units on the outside of the plasma membrane.

• Replicative Cycle of HIV

  • This is followed by fusion of the viral envelope with the cell membrane and the release of the HIV capsid into the cell.
  • The final step of the viral cycle, assembly of new HIV-1 virions, begins at the plasma membrane of the host cell.
  • These are transported to the plasma membrane of the host cell where gp41 anchors gp120 to the membrane of the infected cell.
  • The Gag (p55) and Gag-Pol (p160) polyproteins also associate with the inner surface of the plasma membrane along with the HIV genomic RNA as the forming virion begins to bud from the host cell.

• Viral Exit

  • During this process the virus acquires its envelope, which is a modified piece of the host's plasma or other, internal membrane.
  • The viral envelope is the typical lipid bilayer, derived from the host cell itself and sources usually come from the nuclear membrane, endoplasmic reticulum, Golgi apparatus/body, and plasma membrane.
  • This process will slowly use up the cell membrane and eventually lead to the demise of the cell.
  • This method releases the virus from the infected cell by bursting its membrane and this kills the cell as well.
  • Viral budding uses the host's cell membrane eventually causing cell death.

• Cyanobacteria

  • They are not bounded by lipid membranes but by a protein sheath.
  • As with any prokaryotic organism, cyanobacter does not show nuclei nor internal membranes; many cyanobacter species have folds on their external membranes which function in photosynthesis.
  • In most forms the photosynthetic machinery is embedded into folds of the cell membrane, called thylakoids.
  • Their plasma membrane contains only components of the respiratory chain, while the thylakoid membrane hosts both respiratory and photosynthetic electron transport.

• Adaptive Immunity and the Immunoglobulin Superfamily

  • Immunoglobulins are produced in a membrane-bound form by B lymphocytes.
  • These membrane molecules function as B cell receptors for antigens.
  • The interaction of antigens with membrane antibodies on naive B cells initiates B cell activation .
  • When a B cell encounters its triggering antigen, it gives rise to many large cells known as plasma cells.
  • Every plasma cell is essentially a factory for producing an antibody.

• Iron-Binding Proteins

  • They are carrier proteins (those used to move ions and molecules across membranes) and more generally metalloproteins (those which contain a metal ion cofactor).
  • Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids .