membrane structure Flashcards
selective permeability
allowing some substances to cross more easily than others
amphipathic
containing hydrophobic and hydrophilic regions
fluid mosaic model
a mosiac of protein molecules bobbing in a fluid bilayer of phospholipid
temperature cools
membrane goes from fluid state to solid state
to work properly
membranes must be fluid ( at the right temperature )
what does cholesterol do at warm temperatures
it reduces fluidity
integral proteins
that span the membrane ex:transmembrane protein
hydrophobic regions of integral proteins
consist of one or more stretches of non polar amino acids
peripheral proteins
are loosely bound to the surface of the membrane
six functions of membrane proteins
transport enzymatic activity signaling recognition, intercellular joining and attachment to the cytoskeleton
membrane carbohydrates
with lipids are called glycolipids and with proteins they are called glycoproteins
cross the membrane easy
non polar especially small (carbon dioxide water oxygen urea)
cannot cross the membrane easily
polar and large (sugars and ions)
transport proteins
allow passage of hydrophilic/polar substances across the membrane
aquaporins
facilitate the passage of water
channel proteins
have hydrophilic channels that certain molecules or ions can use as a tunnel
diffusion
molecules spread out evenly in available space
concentration gradient
substances diffuse from where it is more concentrated to where it is less concentrated through the bilayer
passive transport
diffusion or when no energy is used from the cell
facilitated diffusion
speeds transport of a solute by providing efficient passage through the membrane using transport proteins
active transport
moves against the concentration gradient by using proteins and energy
why is a lipid bilayer fluid
because it is held together by hydrogen bonds and so the layer can shift
cholesterol
wedged in the bilayer to regulate under different conditions
