plasma membrane

Examples of plasma membrane in the following topics:

• Components of Plasma Membranes

  • The plasma membrane protects the cell from its external environment, mediates cellular transport, and transmits cellular signals.
  • The plasma membrane (also known as the cell membrane or cytoplasmic membrane) is a biological membrane that separates the interior of a cell from its outside environment.
  • The primary function of the plasma membrane is to protect the cell from its surroundings.
  • Just as a hole in the wall can be a disaster for the castle, a rupture in the plasma membrane causes the cell to lyse and die.
  • Among the most sophisticated functions of the plasma membrane is its ability to transmit signals via complex proteins.

• 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

• Selective Permeability

  • Plasma membranes are asymmetric: the interior of the membrane is not identical to the exterior of the membrane.
  • Carbohydrates, attached to lipids or proteins, are also found on the exterior surface of the plasma membrane.
  • This adds considerably to the selective nature of plasma membranes.
  • Recall that plasma membranes are amphiphilic; that is, they have hydrophilic and hydrophobic regions.
  • The exterior surface of the plasma membrane is not identical to the interior surface of the same membrane.

• Fluid Mosaic Model

  • Nicolson in 1972 to explain the structure of the plasma membrane.
  • Plasma membranes range from 5 to 10 nm in thickness.
  • Proteins make up the second major component of plasma membranes.
  • Carbohydrates are the third major component of plasma membranes.
  • The fluid mosaic model of the plasma membrane describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins.

• Plasma Membrane Hormone Receptors

  • Hormones that cannot diffuse through the plasma membrane instead bind to receptors on the cell surface, triggering intracellular events.
  • Amino acid-derived hormones and polypeptide hormones are not lipid-derived (lipid-soluble or fat-soluble); therefore, they cannot diffuse through the plasma membrane of cells.
  • Lipid-insoluble hormones bind to receptors on the outer surface of the plasma membrane, via plasma membrane hormone receptors.
  • The amino acid-derived hormones epinephrine and norepinephrine bind to beta-adrenergic receptors on the plasma membrane of cells.
  • Describe the events that occur when a hormone binds to a plasma hormone receptor

• The Plasma Membrane and the Cytoplasm

  • The plasma membrane is made up of a phospholipid bilayer that regulates the concentration of substances that can permeate a cell.
  • Despite differences in structure and function, all living cells in multicellular organisms have a surrounding plasma membrane (also known as the cell membrane).
  • In the case of the plasma membrane, only relatively small, non-polar materials can move through the lipid bilayer (remember, the lipid tails of the membrane are nonpolar).
  • The eukaryotic plasma membrane is a phospholipid bilayer with proteins and cholesterol embedded in it.
  • Explain the structure and purpose of the plasma membrane of a cell

• Facilitated transport

  • Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
  • Another type of protein embedded in the plasma membrane is a carrier protein.
  • This adds to the overall selectivity of the plasma membrane.
  • They may cross the plasma membrane with the aid of channel proteins.
  • Some substances are able to move down their concentration gradient across the plasma membrane with the aid of carrier proteins.

• Exocytosis

  • In exocytosis, waste material is enveloped in a membrane and fuses with the interior of the plasma membrane.
  • Next, the vesicle's membrane and the cell membrane connect and are held together in the vesicle docking step.
  • The final stage, vesicle fusion, involves the merging of the vesicle membrane with the target membrane.
  • Some examples of cells using exocytosis include: the secretion of proteins like enzymes, peptide hormones and antibodies from different cells, the flipping of the plasma membrane, the placement of integral membrane proteins(IMPs) or proteins that are attached biologically to the cell, and the recycling of plasma membrane bound receptors(molecules on the cell membrane that intercept signals).
  • In exocytosis, vesicles containing substances fuse with the plasma membrane.

• Membrane Fluidity

  • The mosaic nature of the membrane, its phospholipid chemistry, and the presence of cholesterol contribute to membrane fluidity.
  • First, the mosaic characteristic of the membrane helps the plasma membrane remain fluid.
  • However, because of its mosaic nature, a very fine needle can easily penetrate a plasma membrane without causing it to burst; the membrane will flow and self-seal when the needle is extracted.
  • It lies alongside the phospholipids in the membrane and tends to dampen the effects of temperature on the membrane.
  • The plasma membrane is a fluid combination of phospholipids, cholesterol, and proteins.

• 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.