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what does selectively permeable mean
allows some materials to cross more easily, enables the cell to maintain a unique internal environment
what does fluid mosaic mean
the phospholipid bilayer is always moving, with a mosaic of proteins floating in it
tails of a phospholipid are ____ and the heads are ____
hydrophobic, hydrophilic
cholesterol
acts as fluidity buffer in membrane, restricts phospholipid movement (reducing fluidity at warmer temps), prevents close packing of lipids (enhancing fluidity at colder temps)
integral proteins (transmembrane proteins)
extend through membrane, have two hydrophilic ends and a hydrophobic midsection
peripheral proteins
attached to membrane surface, attach to cytoskeleton and fibers of ECM, provide plasma membrane support
6 major functions of membrane proteins
transport, enzymatic activity, signal transduction, cell to cell recognition, intracellular joining, attachment
membrane carbohydrates
ability of a cell to distinguish other cells is based on recognition of membrane carbohydrates
creation of membranes
protiens and lipids synthesized in the ER, modified in the Golgi, and transported to the membrane by vescicles
which molecules can easily cross through selective permeability
hydrophobic, non polar molecules
transport proteins
provide a passageway to help molecules through the cell, channel and carrier proteins
channel proteins
provides a hydrophilic passageway through the membrane, aquaporins
carrier proteins
physically bind and change shape to shuttle molecules across, glucose transporter
diffusion
movement of a substance down its concentration gradient, form of passive transport
concentration gradient
movement is from areas of high to low concentration
osmosis
diffusion of free water across a selectively permeable membrane, affected by concentration of dissolved solutes
tonicity
tendency of a surrounding solution to cause a cell to gain or lose water- affected by concentration of solutes, can be hypotonic, isotonic, or hypertonic
isotonic
solutions that have equal concentrations with no net movement of water across the membrane
hypertonic
solution with a higher concentration of solutes, water will go out the cell and into the solution, cell could shrivel
hypotonic
solution with lower concentration of solutes, water will go into the cell, could lyse (burst)
turgor pressure
provides mechanical support for the plant, hypotonic environment is healthiest for a plant
healthiest environment for animal cell
isotonic
facilitated diffusion
passive transport aided by proteins (channel proteins)
active transport
requires ATP and moves against its concentration gradient- carrier proteins
electrogenic pumps
membrane proteins that generate voltage across membrane by active transport of ions- sodium potassium pump and proton pump
bulk transport
active, transports larger biological molecules, packaged in vescicles, across the membrane
exocytosis
a cell secretes large molecules by the fusion of vesicles with the plasma membrane out of the cell
endocytosis
a region of the membrane sinks inward and punches off to form a vesicle containing material that had been outside the cell
3 types of endocytosis
phagocytosis, pinocytosis, receptor
phagocytosis
endocytosis of food particles (cellular eating)
pinocytosis
endocytosis of fluids (cellular eating)
receptor
a mediated endocytosis enables a cell to acquire specific substances by ligand binding (molecule to specific receptor)