Membranes

& Cell Transport

LE 3-1

Bonecell

Smoothmuscle

cell

Ovum Sperm

Neuron inbrain Fat cell

Cells liningintestinal tract

Bloodcells

LE 3-2

Cilia

Cytoplasm

Mitochondrion

Nuclearenvelope

surroundingnucleus

Secretoryvesicles

Plasma (cell)membrane

Chromatin (DNA)

What do membranes do?

•Form the boundary between the intracellular compartment and the extracellular environment.

•“Traffic Cop” - Regulate what enters and leaves the cell = “selective permeability.”

•Respond to substances that come in contact with the membrane. Ex: insulin, glucagon, & other hormones

•Secrete (=squeeze out) substances that are synthesized inside the cell.

•Compartmentalize and organize the interior of the cell. Ex: mitochondria, E.R., various vesicles

Early evidence for the bi-layered structure of the plasma membrane came from transmission electron micrographs. This is the plasma membrane of a RBC.

A phospholipid bilayer – This is NOT a functional

membrane

Here is a detailed picture of the way six phospholipid molecules interact with each other and their surroundings to form a phospholipid bilayer.

Phospholipid Animation(Click Here)

LE 3-3

EXTRACELLULAR FLUID

Carbohydratechains

Phospholipidbilayer

Cholesterol

Protein withgated channel CYTOPLASM

Proteins Hydrophilicheads

Cytoskeleton

Proteins

Cellmembrane

Hydrophobic tails

Proteinwith channel

LE 3-5

EXTRACELLULARFLUID

Lipid-soluble molecules, O2 andCO2 diffuse through membranelipids.

Plasma membrane Channelprotein

Largemoleculesthat cannot diffuse throughlipids cannot cross the membraneunless they are transported by acarrier mechanism

CYTOPLASM

Smallwater-solublemolecules andions diffusethroughmembranechannels

LE 3-4

Diffusion = spreading of molecules from a place where the concentration [ ] is higher to a place where it’s lower.

OSMOSIS = diffusion of H2O, across a membrane, from a region of higher [H2O] to a region of lower [H2O].

“[ ]” means “concentration of…”

Gray dots represent solute particles. Solute = anything dissolved in the water.

LE 3-6-1

Watermolecules

Glucosemolecules

A B

Selectively permeable membrane

Two solutions containing different solute concentrations are separated by a selectively permeable membrane. Water molecules (small blue dots) begin to cross the membrane toward solution B, the solution with the higher concentration of solutes (larger pink circles).

LE 3-6-2a

Volumedecreased

At equilibrium, the solute concentrations on the two sides of the membrane are equal. The volume of solution B has increased at the expense of that of solution A.

Volumeincreased

Diffusion & OsmosisAnimations

http://www.biologycorner.com/bio1/diffusion.html

http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf

LE 3-7a

Isotonic

Water molecules

LE 3-7bWater molecules

Hyp0tonic

LE 3-7c

Hypertonic

Solute molecules

Hypertonic

LE 3-8

Glucosemolecule

attaches toreceptor site

EXTRACELLULARFLUID

CYTOPLASM

Receptor site

Carrier protein

Change in shapeof carrier protein

Glucosereleasedinto cytoplasm

LE 3-9

EXTRACELLULAR FLUID

CYTOPLASM

Sodium–potassiumexchange

pump

3 Na+

2 K+ATP ADP

LE 3-10

EXTRACELLULARFLUID

Ligands bindingto receptors

ExocytosisLigand

receptors

CYTOPLASM

Coatedvesicle

Ligands

Endocytosis

Fusion

Lysosome

Fused vesicleand lysosome

Ligandsremoved

Detachment

LE 3-11

EXTRACELLULAR FLUID

Pseudopodium(cytoplasmicextension)

Foreignobject

Vesicle

CYTOPLASM

Undissolvedresidue

LysosomesCell membraneof phagocyticcell

LE 3-12

Microvillus

Microfilaments

Cell membrane

Mitochondrion

IntermediatefilamentsEndoplasmicreticulumSecretoryvesicleMicrotubule

LE 3-14a

Endoplasmic reticulum

Transportvesicle Golgi apparatus Membrane renewal

vesicles

Secretoryvesicles

Lysosomes

CYTOSOL

Vesicleincorporation incell membrane

Cellmembrane

EXTRACELLULARFLUID

LE 3-14b

Exocytosis

Transport TypesAnimations

• http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm