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UNCW BIO 240 - Study Guide 02 - CELLS

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THE CELLULAR LEVEL OF ORGANIZATIONA. GENERALIZED ANIMAL CELLIt 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. Plasma (cell) membrane2. Cytosol3. Organelles4. InclusionsDefine each of the following terms:Plasmalemma -- The plasmalemma (cell or plasma membrane) is theouter 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 betweenthe 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 characteris-tic 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) MEMBRANE1. MEMBRANE CHEMISTRY AND ANATOMYa. MEMBRANE LIPIDS9b. MEMBRANE PROTEINSWhat 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 themolecular 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. Phospholipids (75%) -- hydrophilic “head” and hydrophobic “tails”2. Glycolipids (5%) -- role obscure (cell adhesion, recognition)3. Cholesterol (20%) -- membrane strength and steroid hormone precursorCompare 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 functionsPeripheral proteins do not extend across the lipid bilayer butrather 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.10Receptor -- 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 mem-brane. *ex. small intestinal enzymes for digestion of food)Cytoskeleton anchor -- anchors filaments and tubules of the cytoskeleton inside cell membrane to provide struc-tural stability and shape for the cell. May also partici-pate 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 isthe histocompatibility (MHC) proteins.2. MEMBRANE PHYSIOLOGYa. COMMUNICATIONb. ELECTROCHEMICAL GRADIENTc. SELECTIVE PERMEABILITYList the three major functions of the cell membrane.1. Communication 2. Electrochemical gradient3. Selective permeabilityWith 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 (neurotrans-mitters, 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 inthe 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 11anions 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 substancesdo 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 ionsand 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.12Why are the mechanisms that enable substances to move across cell membranes essential to life?Without


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