transport mechanisms Flashcards
define homeostasis
refers to any process that living things use to actively maintain fairly stable conditions necessary for survival
coined by walter cannon
how to preserve constancy of milieu interieur and the homeostasis
exchange nutrients, salts, gases and waste in and out of the body
what is the cell membrane highly permeable to
H2O
lipid soluble substances
dissolved gasses (O2 and CO2)
small uncharged molecules
what is the cell membrane less permeable to
larger molecules
charged particles
what is the cell membrane impermeable to
very large molecules
describe the cell membrane (plasma membrane)
6-10nM thick (very thin)
bimolecular phospholipid layer (phospholipid bilayer)
amphipathic = polar hydrophilic heads on outside and non polar hydrophobic tails in center
how much of the plasma membrane is phospholipids (by weight)
40-50%
is cholesterol hydrophobic
slightly amphipathic
describe what happens when cholesterol is inserted into the phospholipid bilayer
reduces packing of fatty acid tails
tends to increase membrane fluid it keeping fatty acid tails apart
describe what cholesterol may also be involved in
formation of vesicles that pinch off the plasma membrane in lipid rafts
what does cholesterol do at high temps
acts to stabilize the cell membrane and add firmness
what does cholesterol do at low temps
inserts into phospholipids and prevents them from interfering with each other to avoid aggregation
describe proteins
most diverse macromolecules
25-75% membrane by weight
name the 2 types of proteins
integral and peripheral
describe integral proteins
closely associated with phospholipids
mostly cross cell membrane
trans membrane and amphipathic
embedded transverse the whole membrane
not easily removable
describe peripheral proteins
more loosely associated
mostly on cytoplasmic side
easily removable
located on cell surface
what is glycocalyx (describe it)
layer of carbs formed by chain of monosaccharides
extend from extracellular surface of the cell membrane bound to proteins
what is glycocalyx associated with
glycoproteins and glycolipids
what is the purpose of glycocalyx
provides protection from infection
enables cells to identify each other and interact
describe fluid mosaic model or cell membrane
proteins are fixed and can move around
not a stable situation
membrane is always being replenished and so there’s much more turnover
name the functions of plasma membrane proteins (6)
selective transport channel
enzyme
cell surface receptor
cell surface identity marker
cell adhesion
attachment to the cytoskeleton
describe selective transport channel (functions of plasma membrane)
channels (ion channels) and transporters (ions and other molecules)
transport and diffusion of specific molecules into and out of cell
describe enzyme (functions of plasma membrane)
amino acid transport Na-K pumps
enzymes like ATPase
act as enzymes that catalyze membrane associated reactions
describe cell surface receptor (functions of plasma membrane)
G protein coupled receptors
insulin receptors
ACh receptors
for signaling within cells
serve as receptors for receiving and transducing chemical signals from the cell environment