Membrane Transport

plasma membrane

protective outer layer in all living cells; separates inside from outside

functions of plasma membrane

physical barrier, exchange, communication, attachment

plasma membrane barrier

chemical, not bacterial

plasma membrane permeability

selective; also allows for compartmentalization

phospholipid bilayer

double layer of phospholipid molecules that form core structure of cell membranes

fluid mosaic model

bilayer is flexible, 2D, many molecules, can float and move

fluid

lipid/protein molecules, sliding pas sideways allows for flexibility

mosaic

mixture of many macromolecules is patchwork; carbs, lipids, proteins

parts of phospholipid bilayer

hydrophillic head and hydrophobic tail

hydrophilic head

water loving and polar glycerol and phosphate

hydrophobic tail

water fearing and nonpolar; 2 saturated and unsaturated fatty acids

amphipathic

combines both hydrophobic and hydrophilic

types of plasma membrane proteins

peripheral and integral

peripheral proteins

attach to inner or outer face of membrane and does not protrude

integral protein

protrudes partly or all the way across membrane; channel and carrier proteins

membrane transport

collection of mechanisms that regulate passage of solutes, ions, small molecules across membrane

types of membrane transport

paracellular and transcellular

paracellular transport

goes between cells; less selective

transcellular transport

goes through cells; more selective

selective permeability

property of plasma membrane allowing for certain molecules to pass through while blocking others out

passive transport

no energy needed, goes from high to low concentration gradient

active transport

energy needed and goes against concentration gradient

carrier proteins uses

passive transport via facilitated diffusion or active transport via primary/secondary active transport

channel proteins uses

passive transport only; osmosis and facilitated diffusion

permeable molecules

gases and small lipid soluble compounds

types of passive transport

simple diffusion, osmosis, facilitated diffusion, bulk filtration

ficks law

diffusion is non linear over distance and time

rate of flux equation

directly proportional over inversely proportional

directly related to rate of flux

temperature, lipophilicity, surface area, concentration gradient

inversely related to rate of flux

membrane thickness, molecular size

fick equation

root mean squared (RMS)

ficks law of diffusion

diffusive flux of solute = diffusion coefficient (constant) x concentration gradient

simple diffusion

passive process moves molecules from high to low concentration; rapid over short distance, inversely related to molecular size, open system or partition

osmosis

diffusion of water across selectively permeable membrane affected by osmolarity

osmolarity

number of particles in a solution

tonicity

concentration solutes dissolved in outside of cell determines direction of water movement; outside relative to inside

isotonic

equal solute concentration outside and inside; zero flux

hypertonic

solute concentration higher outside cell; water rushes out of cell and shrinks cell

hypotonic

solute concentration higher inside cell; water rushes inside cell and swells

forces acting on cells

osmotic and hydrostatic force

osmotic force

pressure imposed on cell cause by water diffusion

hydrostatic force

pressure needed by cell to stop osmosis

facilitated diffusion

movement of a molecule in or out of cell, down a concentration gradient; requires carrier protein

bulk filtration

movement of solutes/water in some direction due to pressure gradients, not random motion; high to low pressure and independent of concentration

channel proteins

open fixed shape transport protein allows specific molecules through depending on size, and shape; smaller and less complicated than carriers

carrier proteins

transport proteins that bind to certain molecules and change shape to ferry them across membrane; larger and more complex than channel proteins

types of active transport

primary and secondary

primary active transport

directly consumes ATP to move substance against concentration gradient

example of active transport

Na K pump; 1 molecule ATP moves 3 Na out of cell and 2 K into cell

secondary active transport

used energy in preexisting concentration gradient to transport substance against concentration gradient

secondary active transport explained

another substance is moving down concentration gradient to provide energy for substance to move up concentration gradient

example of secondary active transport

Na and glucose symporter

sequence of amino acids and structure determines

the ions channel proteins transport

structure dictates

function

channel protein gating mechanisms

voltage gated, ligand gated, mechanosensitive

voltage gated

based on charge

ligand gated

chemical messengers attach; extracellular or intracellular

mechanosensitive

pressure or touch sensitive

channel proteins form

a pore; travel faster than carrier

channelopathies

diseases/conditions as a result of ion channel dysfunction

examples of channelopathies

cystic fibrosis , TTX, diabetes

carrier proteins contain a cycle between

multiple conformations where solute binding site is accessible to only one side of membrane or the other ay any time

alternating access model

carrier proteins never have an open channel/pore all the way through the membrane like channels

carrier kinematics

much slower transport speed than channels; 1-3 molecules per cycle vs thousands

types of carrier proteins

symport, uniport, antiport

symport

transport two molecules in same direction at same time; secondary active transport

antiport

transport 2 molecules in opposite direction at same time; primary active transport

uniport

transport only one molecule at a time; primary active transport