cell membranes and transport Flashcards
what type of molecule does the phospholipid component let across the membrane
lipid soluble and not water soluble
what characteristics does a phospholipid molecule have
they can form bilayers - one sheet opposite the other
hydrophillic heads on the inner and outer layers to interact with water in the cytoplasm and outside the cell hydrophobic heads facing inside of cell
what are intrinsic proteins
they extend across both surfaces of the bilayers and include transport proteins which use active or passive transport to move molecules or ions across the membrane
what do extrinsic proteins do
provide structural support and form recognition sites by identifying cells and receptor sites for hormone attatchment
where are extrinsic proteins found
on either surface of the bilayer
where does cholesterol occur in membranes and what is the function
in between the phospholipid molecules
makes the membrane more stable at higher temperatures and more fluid at lower temperatures
what is the glycocalyx
the carbohydrate molecule around an animal cell
some cells form hormone receptors or in cell to cell adhesion
how does the glycocalyx form
when the extracellular proteins are glycosylated
why is the model called fluid mosaic
individual proteins can move relative to their layers (fluid )
embedded proteins in the bilayer vary in shape size and in their distribution between the phospholipids
how do small molecules like o2 get across the membrane
they move between the phospholipid molecules and diffuse across the membrane
how do lipid soluble molecules get across the membrane e.g vitamin a
they dissolve in the phospholipid and diffuse across the membrane
how do water soluble molecules e.g glucose get across the membrane
they cant diffuse so they have to pass though the intrinsic protein molecules which form water filled channels across the membrane so it is selectively permeable to water and some solutes
what factors affect the rate of diffusion
concentration gradient
thickness of exchange surface or distance of travel
surface area of membrane
temperature
size of diffusing molecules
what is simple diffusion
the passive movement of a molecule or ion down a concentration gradient from a region of high to low concentration
what is facilitated diffusion
passive transfer of molecules/ions down a concentration gradient across a membrane by channel or carrier protein molecules in the membrane
what are carrier proteins used for
diffusion of larger molecules e.g sugars and amino acids
what are channel proteins
molecules with pores lined with polar groups/ hydrophillic ions so that water soluble molecules can pass through
