THE CELLULAR LEVEL OF ORGANIZATION A GENERALIZED ANIMAL CELL It is at the cellular level or organization that activities essential to life occur and where disease processes originate A cell is the basic living structural and functional unit of the body All animal cells have four anatomical features in common Name them 1 2 3 4 Plasma cell membrane Cytosol Organelles Inclusions Define each of the following terms Plasmalemma The plasmalemma cell or plasma membrane is the outer limiting membrane that separates the cell s internal components from the extracellular material and external environment Cytoplasm Cytoplasm is the term used for all cellular material between the plasma membrane and the nucleus of the cell Cytosol Cytosol is the thick semi fluid portion of the cytoplasm called the intracellular fluid It contains soluble proteins enzymes ions and nutrients and suspends the organelles Organelles Organelles are highly organized structures with characteristic shapes that are highly specialized for specific activities Inclusions Inclusions are temporary structures suspended or stored within the cytoplasm that contain secretions and storage products of the cell B PLASMA CELL MEMBRANE 1 MEMBRANE CHEMISTRY AND ANATOMY a MEMBRANE LIPIDS 9 b MEMBRANE PROTEINS What is the function of the cell membrane It is the thin barrier that separates the cell s internal fluid from the external fluid It serves as the gatekeeper that regulates passage of substances into and out of the cell Describe the fluid mosaic model of the membrane structure The fluid mosaic model of membrane structure describes the molecular arrangement of the cell membrane The membrane is a mosaic of protein molecules floating like icebergs in a sea of lipid molecules Describe the three types of membrane lipids 1 2 3 Phospholipids 75 hydrophilic head and hydrophobic tails Glycolipids 5 role obscure cell adhesion recognition Cholesterol 20 membrane strength and steroid hormone precursor Compare integral membrane proteins with peripheral membrane proteins Integral proteins extend across the lipid bilayer into the extracellular fluid on one side and into the intracellular fluid on the other They have a number of functions Peripheral proteins do not extend across the lipid bilayer but rather are loosely attached to either the inner or outer surfaces of it Their roles in cell function remain obscure Describe the functions of the following membrane proteins Channels pore allows a specific substance to move through water filled passageways Most cell membranes include specific channels for several ions Most common are for Na and K Transporter carrier transports specific substances across membrane by changing shape For example amino acids needed to synthesize new proteins enter body cells via transporter 10 Receptor recognizes a specific ligand and alters the cell s functions in some way For example this is a classic mechanism by which protein based hormones affect cells Enzyme catalyzes reactions inside or outside depending upon which direction the active site faces the membrane ex small intestinal enzymes for digestion of food Cytoskeleton anchor anchors filaments and tubules of the cytoskeleton inside cell membrane to provide structural stability and shape for the cell May also participate in movement of the cell Cell identity markers distinguish your cells from anyone else s unless you are an identical twin and from microbial cells An important class of such markers is the histocompatibility MHC proteins 2 MEMBRANE PHYSIOLOGY a COMMUNICATION b ELECTROCHEMICAL GRADIENT c SELECTIVE PERMEABILITY List the three major functions of the cell membrane 1 2 3 Communication Electrochemical gradient Selective permeability With what must cells of the body be able to communicate The cell via the plasma membrane communicates with other body cells foreign cells and ligands neurotransmitters enzymes hormones nutrients and antibodies in the extracellular fluid Describe the chemical and electrical components of the electrochemical gradient formed by the cell membrane The chemical portion of the gradient is formed because the membrane maintains very different chemical compositions in the cytosol and the extracellular fluid The major extracellular cation is Na and the major anion is Cl The major intracellular cation is K and the major 11 anions are organic phosphates and amino acids The electrical gradient arises because the inside of the membrane is more negatively charged than the outside As a result there is a voltage voltage is electrical potential or potential difference as expressed in volts called the membrane potential across the membrane The third major function of the cell membrane is to provide selective permeability What is this The plasma membrane regulates the entry and exit of materials by permitting certain substances to pass freely while restricting the passage of others This property is called selective permeability A membrane is said to be permeable to a substance if It allows that substance free passage into and out of the cell Permeability of a membrane is dependent upon four factors that relate to membrane structure List and describe these factors 1 Solubility in lipids Substances that dissolve in lipid pass easily across the membrane while water soluble substances do not For example oxygen is fat soluble and crosses the membrane easily glucose is water soluble and does not cross the membrane 2 Size Ions and molecules less than 8 Angstroms in diameter can cross the cell membrane freely Substances larger than 8 Angstroms are restricted from crossing the membrane because they are too large to pass between the molecules that form the membrane itself 3 Charge The membrane is impermeable to all charged ions and molecules However the overall negative membrane potential of most cells aids the influx of cations and hinders the influx of anions 4 Presence of specific channels or transporters Channels increase membrane permeability for some substances by providing specific routes of entry or exit This is done by either attaching to and shuttling the substances through the channel or by simply letting it pass through the channel s water filled space 12 Why are the mechanisms that enable substances to move across cell membranes essential to life Without these mechanisms the cell would be unable to procure oxygen nutrients etc or rid itself of carbon dioxide and other waste products of metabolism C MOVEMENT OF MATERIALS ACROSS THE PLASMA