ch 7: membrane structure + function

fluid mosaic model

membranes are a fluid bilayer w/ diff proteins embedded

peripheral proteins

attached to membrane surface

integral proteins

embedded in membrane

transmembrane proteins

integral proteins that span entire membrane

glycolipids

carbohydrates bonded to lipids

glycoproteins

carbohydrates bonded to proteins

selective permeability

some substances cross more easily than others; plasma membrane

transport protein

helps hydrophilic substances across the membrane; are specific

channel protein

provides a hydrophilic passage; allows specific molecules or ions to cross

diffusion

movement of molecules from high to low concentration; down concentration gradient

passive transport

diffusion of a substance across a membrane w/ no energy investment

osmosis

diffusion of water across a selectively permeable membrane; moves toward side with higher solute concentration

isotonic solution

solute concentration is same inside and out ; no net movement of water

isotonic solution - animal cell

normal

isotonic solution - plant cell

flaccid

hypertonic solution

solute concentration is HIGHER outside; water moves OUT of cell

hypertonic solution - animal cell

shriveled

hypertonic solution - plant cell

plasmolyzed

hypotonic solution

solute concentration is LOWER outside; water moves INTO the cell

hypotonic solution - animal cell

may lyse

hypotonic solution - plant cell

turgid/normal

aquaporins

facilitate the diffusion of water

ion channels

facilitate the transport of ions

gated channels

some ion channels can be open or close due to stimulus

carrier protein

binds specific molecules; changes shape to move them across membrane

active transport

moves solutes against their gradients; low→high; requires energy (usually from ATP hydrolysis)

sodium-potassium pump

specific example of active transport

membrane potential

voltage across a membrane; created by differences in distribution of positive and negative ions

ion movement - chemical force

concentration gradient

ion movement - electrical force

membrane potential

ion movement - electrochemical gradient

ion diffuses DOWN

cotransport

using one gradient to move another molecule

bulk transport

large molecules are moved across plasma membrane in vesicles; requires energy

exocytosis

molecules move OUT of the cell; fuses w/ the plasma membrane to be released out

endocytosis

molecules move INTO the cell; plasma membrane folds inwards and forms a vesicle; phagocytosis, pinocytosis, & receptor-mediated endocytosis

what determines permeability?

structure

what can cross the membrane easily?

hydrophobic/nonpolar molecules (dissolves through lipid bilayer)

what can’t cross the membrane easily?

hydrophilic molecules (ex. ions, polar molecules)