the basic structural and functional unit of life
the function of cellular organelles
1. plasma membrane 2. cytoplasm 3. nucleus
separates the cell from its surrounding environment
thick gel-like substance inside of the cell composed of numerous organelles suspended in watery cytosol
large membranous structure near the center of the cell that houses the DNA
functions of the plasma membrane
the outer limit of the cell, physical isolation, regulates exchange with environment, monitors the environment, structural support
structure of the plasma membrane in lipids
make up the bulk of the membrane and form the main structural barrier (phospholipids, cholesterol)
structure of the plasma membrane in proteins
integrated throughout the membrane; may span the entire width or be attached to one surface only
structure of the plasma membrane in carbohydrate complexes
found only attached to the outside surface (glycoproteins, glycolipids)
primary structure deature of the membrane is phospholipid bilayer. hydrophilic heads towards the watery environement on both sides, hydrophobic fatty-acid tails inside the bilater. acts s a bartrier to the movement of ions and water soluble compounds.
fuction of cholesterol in the phospholipid bilayer
help maintain fluidity by preventing the phospholipid tails from packing together too tightly in cold and binds them together to prevent excess movement when warm.
float within the phospholipid bilayer
span the membrane
associated with inner or outer surface of the membrane but do not penetrate the entire width of the membrane.
six functions of membrane proteins
1. transport (channel or carrier molecules) 2. receptors for signal transduction (docking sites for hormones and drugs) 3. cell to cell interactions (involved in cellular recognition) 4. enzymes 5. intercellular junctions 6. anchoring sites for the cytoskeleton (internally) or extracellular matrix (externally)
a layer of glycoproteins and glycolipids on the outside surface of the cell. Helps stabilize the cell in its environment and contains specific biological markers by which cells recognize one another.
cell adhesion molecules (CAM)
found in the glycocalyx, anchor cells to extracellular matrix, guide movement of cells (embryonic development), transmit mechanical stress to the cytoskeleton
found in the glycocalyx, work in contact signaling - immulogic surveillance, and chemical signaling- ligands attach to surface receptors
types of membrane junctions
1. desomosomes 2. tight junctions 3. gap junctions
rivets adjacent cells together, internally connected intermediate filaments that act as guy wires, found in tissues that experience mechanical stress (eg skin)
impermeable union that encricles the cell, prevent passage of materials between cells, found in hollow fluid filled organs (eg bladder)
hollow cylinders that form a cytoplasmic bridge between cells, found in electrically excitable tissue (muscle).
passive mebrane transport processes
diffusion across a membrane: simple diffusion, facilitated diffusion (channel and carrier-mediated), osmosis. Filtration: bulk flow of fluid/solutes in response to a hydrostatic pressure gradient across a membrane.
active membrane transport processes
carrier mediated active transport, transport by vesicles
net movement of solutes down a concentration gradient. does not require the input of energy to occur
factors affecting diffusion rates of solutes
molecule size (smaller=faster), temperature (hotter=faster), gradient size (larger=faster), eletrical forces (opposites attract, like charges repel, "electrochemical gradients")
movement directly through the phospholipid bilayer, does not require a protein channel or carrier. Lipid soluble comounds (alcohols, fatty acids, steroids), dissolved gases (oxygen and carbon dioxide), water
allows some materials to move more freely than others, degree is based on size, lipid solubility, electical charge (nonpolar>polar>ionic)
protein molecules form ports that allow substance to bypass the phospholipids. Used for ions and large molecules, allow transport to occur at a faster rate than simple diffusion.
special water channels that are used for facilitated diffusion, abundant in red blood cells and in the cells of renal tubules.
two types of protein ports
1. carriers 2. channels
carrier protein ports
proteins undergo a physical change to move a substance across the membrane
channel protein ports
proteins form a pore though the membrane
characteristics of transport carriers
specific, exhibit saturation kinetics, subject to regulation (competition, inhibitor), some are involed in active transport processes
diffusion of water across the cell mebrane. more solute molecules = higher osmotic pressure. water molecules diffuse across membrane toward solution with more solutes.
the measure of the amount of pull a solution has on water. equal to the hydrostatic pressure needed to block osmosis from occuring between two compartments.
a measure of the total solute concentration in an aqueous solution
two fluids that have the same osmostic pressure
has a greater pull on water molecules than another solution
has a lesser pull on water molecules than another solution
the ability of a solution to change the volume (tone or internal tension) of a cell
the passage of water and solutes through a membrane by hydrostatic pressure. pressure gradient pushes solute containing flui from a higher pressure area to a lower pressure area (bulk flow). non selective process, primary menas of moving solutes and fluid from the capillary to the interstitial space.
bulk transport of larger substances or substances moved in bulk across the membrane
utilizes a protein carrier complex in the membrane. moves substates against concentration gradients. requires energy such as ATP
primary active transport
directly uses ATP to move substrates against a concentration gradient
secondary active transport
uses energy stored in the gradient to move substrates against a concentration gradient
two substances are moved across a membrane by one carrier in the same direction
two substances are moved across a membrane by the same carrier in opposite directions. (eg Na+ K+)
bulk transport that is receptor mediated, brings things into the cell, eg pinocytosis and phagocytosis
bulk transport that moves things out of the cell
membrane vesicles move substances from one area in the cell to another
vesicle takes drinks of extracellular fluid, involves non-specific uptake of solutes that occurs with the uptake of fluid
substance never physically crosses though the phospholipid bilayer, it physically drops into the cell surround by membrane
receptor mediated endocytosis
a substance is selectively brought into the cell because it adheres to the receptors on the cell surface
used to secrete hormones, other cell products, and waste. adds new membrane to the plasma membrane
moves small packets of membrane vesicles from one organelle in the cell to another or to the plasma membrane. eg movement of vesicles between ER and golgi