Chapter 7- Membrane Structure and Function

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)