A&P 3: Cells - The Living Units Flashcards
Cells
structural units of all living things
Cell Theory
4 concepts collectively called this; (1) a cell is the basic structural and functional unit of living organisms; define cell properties –> define properties of life (2) activity of an organism depends on both the individual and the collective activities of its cells (3) according to the principle of complementarity of structure and function, the biochemical activities of cells are dictated by their shapes or forms & by the relative number of their specific subcellular structures, & (4) continuity of life from one generation to another has a cellular basis
Generalized (composite) cell
3 main parts of a human cell - plasma membrane, cytoplasm, & nucleus
Plasma membrane
flexible structure that defines the extent of a cell, thereby separating 2 of the body’s major fluid compartments (intracellular & extracellular fluids)
Fluid Mosaic Model
model depicting the plasma membrane as an exceedingly thin (7-10nm) structure composed of a bilayer of lipid molecules with protein molecules plugged into or dispersed in it; constantly changing
Hydrophilic
each lollipop-shaped phospholipid molecule has a polar head that is charged and loves water
Hydrophobic
each phospholipid molecule has an uncharged, nonpolar tail that is made of 2 fatty acid chains and hates water
Glycolipids
lipids with attached sugar groups found only on the outer plasma membrane surface; account for 5% of total membrane lipids
Integral proteins
proteins that are firmly inserted into the lipid bilayer; most are transmembrane proteins (span the entire membrane and protrude on both sides)
Peripheral proteins
proteins not embedded in the lipid bilayer; attach loosely to integral proteins and are easily removed without disrupting the membrane; include a network of filaments that helps support the membrane from its cytoplasmic side; some are enzymes, others are motor proteins involved in mechanical functions, others link cells together
Lipid rafts
20% of the outer membrane surface; dynamic assemblies of saturated phospholipids (which pack together tightly) associated with unique lipids called sphingolipids and lots of cholesterol; more stable, less fluid than the membrane; can include/exclude specific proteins; assumed to be concentrating platforms for cell signaling, membrane invagination, or other functions
Glycocalyx
fuzzy, sticky, carbohydrate-rich area at the cell surface; “sugar-coating”; provides highly specific biological markers by which approaching cells recognize each other
Tight junction
series of integral protein molecules in the plasma membranes of adjacent cells fuse together, forming an impermeable junction that encircles the cell; help prevent molecules from passing through the extracellular space between adjacent cells
Desmosomes
anchoring junctions; mechanical coupling scattered like rivets along the sides of abutting cells to prevent their separation; “binding bodies”; abundant in tissues subjected to great mechanical stress (skin/heart muscle)
Gap junction (nexus)
communicating junction between adjacent cells; cells connected by hollow cylinders (connexons) of transmembrane proteins; ions, simple sugars, and other small molecules can pass through; present in electrically excitable tissues (heart, smooth muscle)
Interstitial fluid
extracellular fluid derived from blood
Selectively (differentially) permeable
describes the plasma membrane; allows some substances to pass while excluding others
Passive processes
substances cross the membrane without any energy input from the cell
Active processes
the cell provides the metabolic energy (usually ATP) needed to move substances across the membrane
Diffusion
tendency of molecules/ions to move from an area of higher concentration to an area where they are in lower concentration
Concentration gradient
difference in the concentration of a particular substance between 2 different areas
Simple diffusion
nonpolar and lipid-soluble substances diffuse directly through the lipid bilayer (oxygen, CO2, and fat-soluble vitamins)
Facilitated diffusion
movement through the plasma membrane by a passive process in which the transported substance either binds to protein carriers in the membrane and is ferried across or moves through water-filled protein channels
Carriers
transmembrane integral proteins that are specific for transporting certain polar molecules or classes of molecules (sugars, amino acids) that are too large to pass through membrane channels