membrane protein

Examples of membrane protein in the following topics:

• Fluid Mosaic Model

  • The proportions of proteins, lipids, and carbohydrates in the plasma membrane vary with cell type.
  • The mitochondrial inner membrane contains 76% protein and 24% lipid.
  • Proteins make up the second major component of plasma membranes.
  • Some complex proteins are composed of up to 12 segments of a single protein, which are extensively folded and embedded in the membrane.
  • Integral membrane proteins may have one or more alpha-helices that span the membrane (examples 1 and 2), or they may have beta-sheets that span the membrane (example 3).

• Facilitated transport

  • Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
  • Unlike simple diffusion where materials pass through a membrane without the help of proteins, in facilitated transport, also called facilitated diffusion, materials diffuse across the plasma membrane with the help of membrane proteins.
  • Another type of protein embedded in the plasma membrane is a carrier protein.
  • They may cross the plasma membrane with the aid of channel proteins.
  • Carrier proteins change shape as they move molecules across the membrane.

• Immunoblot Procedures

  • After this, they are transferred to a synthetic membrane via dry, semi-dry, or wet blotting methods.
  • As the proteins migrate out of the gel, they are captured on a membrane.
  • Protein binding to the membrane is an irreversible mechanism.
  • Membranes can be of the nitrocellulose, polyvinylidene difluoride (PVDF), or nylon variety.
  • This is followed by probing with antibodies specific to the protein being studied on the membrane, a method that is similar to immunohistochemistry, but without a need for fixation.

• 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.
  • This stage of exocytosis is then followed by vesicle priming, which includes all of the molecular rearrangements and protein and lipid modifications that take place after initial docking.
  • 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).

• Selective Permeability

  • In fact, there is a considerable difference between the array of phospholipids and proteins between the two leaflets that form a membrane .
  • On the interior of the membrane, some proteins serve to anchor the membrane to fibers of the cytoskeleton.
  • There are peripheral proteins on the exterior of the membrane that bind elements of the extracellular matrix.
  • Carbohydrates, attached to lipids or proteins, are also found on the exterior surface of the plasma membrane.
  • Simple sugars and amino acids also need help with transport across plasma membranes, achieved by various transmembrane proteins (channels).

• Basement Membranes and Diseases

  • The two layers are collectively known as the basement membrane.
  • Basement membrane proteins have been found to accelerate differentiation of endothelial cells.
  • Goodpasture disease is the result of an autoimmune response directed at Collagen type IV alpha-3-binding protein, resulting in damage to the lungs and kidneys, bleeding and kidney failure.
  • Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of vertebrates.
  • It is the main component of connective tissue, and is the most abundant protein in mammals.

• Components of Plasma Membranes

  • 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.
  • Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells.
  • Among the most sophisticated functions of the plasma membrane is its ability to transmit signals via complex proteins.
  • Marker proteins on human red blood cells, for example, determine blood type (A, B, AB, or O).
  • The plasma membrane is composed of phospholipids and proteins that provide a barrier between the external environment and the cell, regulate the transportation of molecules across the membrane, and communicate with other cells via protein receptors.

• Plasma Membrane Hormone Receptors

  • Lipid-insoluble hormones bind to receptors on the outer surface of the plasma membrane, via plasma membrane hormone receptors.
  • When a hormone binds to its membrane receptor, a G protein that is associated with the receptor is activated.
  • G proteins are proteins separate from receptors that are found in the cell membrane.
  • The activated G protein in turn activates a membrane-bound enzyme called adenylyl cyclase.
  • Cellular responses to hormone binding of a receptor include altering membrane permeability and metabolic pathways, stimulating synthesis of proteins and enzymes, and activating hormone release.

• Membrane Fluidity

  • First, the mosaic characteristic of the membrane helps the plasma membrane remain fluid.
  • The integral proteins and lipids exist in the membrane as separate but loosely-attached molecules.
  • Cholesterol also serves other functions, such as organizing clusters of transmembrane proteins into lipid rafts.
  • The plasma membrane is a fluid combination of phospholipids, cholesterol, and proteins.
  • Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.

• 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 membrane basically protects the cell from outside forces.
  • It consists of the lipid bilayer with embedded proteins.
  • It appears to bind to the membrane causes rapid depolarization, resulting in a loss of membrane potential leading to inhibition of protein, DNA and RNA synthesis, which results in bacterial cell death.
  • Diagram of a typical gram-negative bacterium, with the thin cell wall sandwiched between the red outer membrane and the thin green plasma membrane.