PNB Quiz Week 5

characteristics of plasma membrane

fluid, composed of many biomolecules, double-layered, composed of fats + lipids (mostly phospholipids)

amphipathic

phospholipids have hydrophilic (polar) heads and hydrophobic (nonpolar) tails

peripheral proteins

only on one side of the membrane, either inner or outer

integral proteins

pass through the membrane on both sides

types of integral proteins

channel and carrier proteins

functions of the plasma membrane

physical barrier, communication, exchange (selectively permeable), attachment

what does the plasma membrane NOT do?

determine the shape of the cell

paracellular transport

molecules move between cells

transcellular transport

molecules move through the cell membrane, more selective bc cells have to cross 2 membranes

what kinds of molecules can pass through the membrane?

gases, small lipid soluble molecules

passive transport

no energy is needed, molecules are moving from a high to a low concentration

active transport

requires energy, can move molecules independent of their concentration gradient

examples of passive transport

simple diffusion, osmosis, facilitated diffusion, bulk filtration

diffusion

random movement of molecules (brownian motion), non-linear over distance + time (nonlinear relationship)

7 properties of simple diffusion

passive, high to low concentration, need concentration gradient, rapid over short distances, direct relation to temp, inversely related to molecular size, in an open system or across a partition

Fick’s Law of Diffusion

diffusion flux = diffusion coefficient (variable) x concentration gradient

increased surface area

maximizes diffusion rate

osmosis

the diffusion of water across a selectively permeable membrane

osmolarity

the # of particles in a solution

solutes ________ water concentration

lower

tonicity

the relationship between volume and solute concentration

hypertonic

water moves out of the cell, cell shrinks (higher concentration outside)

isotonic

no change in cell volume, equilibrium

hypotonic

fewer solutes outside of cell, higher inside, water flows in the cell, cell swells

osmotic force

created by diffusion of water

hydrostatic force

pressure required to block osmosis (created by fluid kept under pressure)

facilitated diffusion

requires a carrier protein (ex. glucose is large, needs help to cross membrane)

bulk filtration

movements of solutes and/or water in the same direction, only form of passive transport that doesn’t require a concentration gradient, as pressure equalizes, solutes go with it

ion channels

form a pore/tunnel through the plasma, usually not open all of the time (gated mechanism)

are ion channels active or passive?

always passive

voltage gated ion channels

changes in charge environment open the gate

ligand-gated

binding of chemical messengers opens gates

mechanosensitive

physical structure of cell changes to open gate

channelopathies

diseases and disorders that are the result of ion channel dysfunction (ex. TTX, toxin and drug targets)

carrier/transporter mediated transport

facilitated diffusion, requires use of transporter

alternating access model

there is never a continuous path all the way through the membrane, solutes have to bind to transporters to get into carrier proteins

occlusion state

state that the solute is not accessible outside or inside of the cell

is transport rate slower with channels or carriers?

carriers - limited # of binding sites

are carriers or channels larger?

carriers

uniport

one solute moved in one direction

symport

two solutes in one direction

antiport

two solutes in opposite directions

active transport

movement against the concentration gradient, requires energy

primary active transport

directly consumes ATP (uniports/antiporters)

secondary active transport

uses energy stored in a pre-existing concentration gradient

examples of primary active transport

sodium potassium pump (3Na/2K/ATPase) - antiporter, requires energy to work

secondary active transport

movement down concentration gradients, provides energy to move other solutes up concentration gradients, most are symporters

what do active transporters do?

help set and maintain concentration gradients for passive transporters