3.4 The Cell Membrane

3.4 The Cell Membrane

  • By the end of this section, you will be able to understand the fluid mosaic model of the cell and its function in the environment.
  • Cells take in and excrete other substances in controlled quantities.
    • The borders of cells are not static but are dynamic and constantly changing.
    • Red blood cells and white blood cells can change their shape as they pass through narrow capillaries if the plasma membrane is flexible.
    • There are more obvious functions of a plasma membrane.
    • As tissues and organs form during early development, and as the immune response plays a role in the "self" versus "non-self" distinction of the immune response, markers that allow cells to recognize one another are vital.
  • The cells have attachment sites for substances that interact with them.
    • Each receptor is designed to bind with a specific substance.
    • These pathways are important for providing the cell with energy, making specific substances for the cell, or breaking down cellular waste or toxins.
    • The hormones and neurotransmitters are able to be transmitted into the cell because of the Receptors on the exterior surface.
    • Viruses use some recognition sites as attachment points.
    • Viruses may evolve to mimic the specific substance that the receptor is meant to bind in order to gain entry to a cell.
    • The specificity helps to explain why specific cells are the only ones affected by the human immunodeficiency virus.
  • The model proposed by Singer and Nicolson better explained both the function and the observations of the plasma membrane.
    • Over time, the model has evolved, but still best accounts for the structure and functions of the plasma membrane as we now understand them.
    • The fluid mosaic model shows that the structure of the plasma membrane is a mosaic of components that are able to flow and change position.
    • The conjugates are able to diffuse quickly in the membrane.
    • The activity of certain enzymes and transport molecules can be done in a certain way.
  • There is a range of 5 to 10 nm thick.
    • The human red blood cells, visible via light microscopy, are approximately 8 um thick, or 1,000 times thicker than a plasma membrane.
  • The fluid mosaic model of the structure shows a fluid combination of cholesterol, conjugates of cholesterol, and conjugates of conjugates of conjugates.
  • In animal cells, cholesterol is embedded in the bilayer of phospholipids.
    • The amount of cholesterol in the animal's blood is regulated by the temperature of the cell's environment.
    • Animals that live in cold climates have more cholesterol in their cells.
  • The main fabric of the cell is composed of two layers of phospholipid molecule, and the polar ends of these molecule are 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- The surfaces of the plasma membrane are made of water.
    • The interior of the membrane is a nonpolar region because of the fatty acid tails.
    • The region has no attraction for water.
  • The second major chemical component of the system is theProteins are the second major chemical component of the system.
    • All or part of the plasma membrane may be covered by the instuments.
    • Materials can be moved into or out of the cell through channels or pumps.
    • On the exterior or interior surfaces of the membranes, there are either integral or peripheral proteins.
    • Structural attachment for the fibers of the cytoskeleton or as part of the cell's recognition sites may be served by both integral and peripheral proteins.
  • The third major component isCarbohydrates.
    • They are found on the exterior surface of cells and either form glycoproteins or form glycolipids.
    • The 2-60 monosaccharide units may be straight or branched.
    • Carbohydrates form on the cell surface to allow cells to recognize each other.
  • Viruses can exploit specific glycoproteins on the surface of host cells to cause diseases.
    • T-helper cells and monocytes, as well as some cells of the central nervous system, can be penetrated by HIV.
    • The virus only attacks the cells in the body.
  • The cells have binding sites on their surfaces that the viruses have exploited with equally specific glycoproteins in their coats.
    • The cell is tricked by the mimicry of the virus coat molecule.
    • The human immune system is stimulated by other recognition sites on the virus's surface.
  • Antibodies are made by reacting to the antigens.
    • The same sites serve as places for the immune system to attach to the virus.
  • The production of an effective vaccine against HIV is very difficult due to the rapid change of genes.
    • There are different populations of the virus that can be distinguished by differences in these recognition sites.
    • The effectiveness of the person's immune system in attacking the virus is decreased by the rapid change of viral surface markers.
  • The CD4 receptor is a glycoprotein on the surface of T cells that HIV can bind to.