Exam 1 Review:  Chapter 3 - The Cell and Membrane Structure

cell - The smallest structural unit of an organism which is capable of independent functioning, (i.e., it has an independent metabolism and the capacity to reproduce (with a few exceptions within the human body)); it consists of one or more nuclei, cytoplasm, and various internal organelles, all surrounded by a semipermeable plasma cell membrane; it is capable, either independently and alone, or interacting with other related units of performing all the fundamental functions of life; "the unit of life."   [Note: All cells have their origin in the primary cell from which the organism was developed.]

cytology - The branch of biology which deals with the formation, structure (emphasizing internal cytoplasmic structure), function, multiplication, pathology, and life history of cells; as a clinical science, it implies the use of the light or electron microscope for the study of cell morphology.

plasma membrane = cell membrane = plasmalemma - The semipermeable lipid bilayer ("fluid-mosaic" model design), composed of phospholipids, glycolipds and cholesterol with associated integral and peripheral proteins, which encloses the cytoplasm of a cell, controls passage of substances in and out of the cell, and serves as a dynamic communication and recognition structure for intercellular cooperation. 

cytosol = cytoplasm - The aqueous solution of an organized complex of inorganic and organic substances located between the outer cell membrane and the nuclear membrane of a cell which is usually in a gel state and has distributed within it various inclusions and granules, the elements of the cytoskeleton and various membrane-bound and non-membrane-bound cell organelles; it is the site of most of the biochemical metabolism of the cell.

organelle - Any of the differentiated specialized structures within a cell, usually located in the cytoplasm, but in some instances, located within the nucleus or cell membrane, which perform a specific function; e.g., a mitochondrion, ribosome, vacuole, lysosome, flagellum, endoplasmic reticulum, or Golgi apparatus.

inclusion - Any material in the protoplasm of a cell, such as pigment granules, fat droplets, or nutritive substances, which represent relatively concentrated collections of one or a few molecular types which are not membrane-bound and are often simply storage accumulations; they may also be abnormal structures such as the sites of viral reproduction within an infected cell or the accumulation of abnormal materials in a cancer cell.

fluid mosaic model - The accepted general model for the molecular structure of cellular membranes consisting of a lipid bilayer containing phopholipids, glycolipids, and cholesterol as a matrix in which various integral and peripheral proteins are located to provide specific functions to specific regions of a membrane; the model is "fluid" because the lipids and proteins can move around with respect to one another and it is a "mosaic" because the characteristic that different arrangements of kinds of lipids and proteins are possible.

phospholipid bilayer - The basic structural medium of all cell membranes; all* the membrane lipids are amphipathic molecules and form two sheets which are one molecule thick and the lipid components are oriented with their polar heads facing the water at either surface while their nonpolar tails or rings are facing each other and the interior of the membrane; smaller numbers of membrane proteins are distributed within the lipids and are the major determinants of local membrane functions.  [*Note:  the majority of the membrane lipids (~75%) are the  phospholipids with smaller quantities (~5%) of glycolipids and cholesterol (~20%) interspersed.]

glycolipid - Any lipid molecule which contains one or more carbohydrate groups, usually in the form of short, branched chains of simple sugars which are hydrophilic and, therefore, contribute to the amphipathic properties of the molecules; the sugar side-chains are covalently bonded to the lipid; they comprise ~5% of cell membrane lipids; some are found in higher concentrations in nervous tissue, e.g., sphingolipids, cerebrosides and gangliosides; some are used in the synthesis of eicosanoid local hormones; others are important components of bile, lung surfactant, and bacterial cell wall.

cholesterol - A multiple (4-membered) carbon-ring lipid molecule which serves as a minor (~20% of membrane lipids) structural component in cell membranes and is also the precursor for synthesis of estrogen, testosterone, aldosterone, cortisol, cortisone, and related steroid hormones.

integral protein - Any of a very diverse group of proteins associated with cell membranes; their structures include many amino acids with hydrophobic side chains which allow the protein to reside embedded within the lipid bilayer of the membrane due to hydrophobic attractions with the lipid molecules; they may or may not span the entire width of the membrane; they may or may not have ends which extend out beyond one or both faces of the membrane; they are often tied internally to the cytoskeleton; their functions include channels, transporters, receptors, intercellular junctions, enzymes, cytoskeleton anchors and cell identity markers.

glycoprotein - Any polypeptide molecule which contains one or more carbohydrate groups, usually in the form of short, branched chains of 8-10 simple sugars covalently attached to one or more R-groups of the constituent amino acids; many are components of the outer face of cell membranes; others are the majority of secreted proteins, e.g., most plasma proteins and most proteins found in mucous secretions; solutions of glycoproteins usually exhibit high viscosity.

peripheral protein - Any of a very diverse group of proteins associated with cell membranes; they reside on either surface of the lipid bilayer of the membrane due to various attractions with the polar heads of the membrane lipid molecules or with the exposed faces of integral membrane proteins; they may be tied internally to the cytoskeleton; their functions include channels, transporters, receptors, intercellular junctions, enzymes, cytoskeleton anchors and cell identity markers.

cytoskeleton anchors - Integral or peripheral proteins on the cytoplasmic face of a cell membrane which unite with cytoplasmic proteins such as microtubules or microfilaments and therefore contribute to the overall shape of the cell.

intercellular junction - Any specialized region of connection between two adjacent cells; usually they are formed by bonds between various membrane proteins; their functions may be purely structural, to hold the cells in position (e.g., desmosomes and tight junctions), or they may permit exchange of materials and serve communication functions (e.g., gap junctions).

cell identity marker - Integral or peripheral proteins or glycoproteins on the cytoplasmic face of a cell membrane which serve as ligands for cell-to-cell recognition in various regulated functions; clinical examples include RBC blood group identity markers (ABO system, Rh system, etc.) and tissue transplant marker (HLA system, etc.) which are also involved in recognition by the immune system.

cell adhesion molecules (CAMS) - Any of a very diverse group of proteins associated with functions in which one molecule must bind, either temporarily or permanently with another molecule in the organism, examples include intercellular junction proteins, antibody molecules, immune cell surface marker proteins, proteins involved in leukocyte migration, etc.; abnormalities in the structure and function of some of these proteins are characteristic of cancerous transformations of cells.

List:

1. three important physiological processes of the cell's outer plasma membrane.

          (1)  serves as a physical barrier between the inside and outside of the cell.
          (2)  serves as a selectively permeable filter, permitting the passage of some substances across the membrane, while restricting others.
          (3)  receives and transmits regulatory instructions to the interior of the cell by interacting with external signal compounds (hormones, neurotransmitters, etc.)

2. the biological compounds (organic molecules) found in cell membrane by category or class and give specific examples of each.

          (1)  lipids (phospholipids, glycolipids, cholesterol, etc.)
          (2)   proteins (integral and peripheral proteins with a wide variety of functions (see Q.3. below for those functions)

3. the functions of membrane proteins.

          channels, transporters, receptors, intercellular junctions, enzymes, cytoskeletal anchors, cell identity markers

4. four factors that determine the permeability of a substance across plasma membrane.

          molecular size - lipid solubility - charge - availability of specific membrane channels or transporters for the substance

15. three types of structural lipids found in cell membrane.

          phospholipids - glycolipids - cholesterol

16. two types of membrane proteins based on their location in cell membrane.

          integral proteins - peripheral proteins

17. seven types of membrane proteins based on their functions in cell membrane.

          channels - transporters - receptors -  intercellular junctions - enzymes - cytoskeleton anchors - cell identity markers.

Sketch and Label:

 1. a fluid mosaic model of cell membrane.

Explain:

1. Three roles of cell membrane proteins in "cell-environment" interactions.

2. The endomembrane system.

The endomembrane system is a collection of membrane-bound organelles involved in molecular transport within the cell.  The main components are the nuclear envelope, endoplasmic reticulum, Golgi bodies, vesicles, and cell membrane.  Only the nucleus has a double membrane; all the other organelles have single membrane boundaries.  Members of the endomembrane system pass various materials to each other either through direct contact or through the use of vesicles.  See diagram below.  This diagram shows how material flows through the members of the endomembrane system. The arrows indicate the direction of flow, which in this example is export of synthesized molecules from the cell.  [Mitochondria are self contained and are not generally thought of as part of the endomembrane system.]