Membranes & Cell Transport

LE 3-1 Bone cell Smooth muscle cell Ovum Sperm Neuron in brain Fat cell Cells lining intestinal tract Blood cells

LE 3-2 Cilia Cytoplasm Mitochondrion Nuclear envelope surrounding nucleus Secretory vesicles 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 Carbohydrate chains Phospholipid bilayer Cholesterol Protein with gated channel CYTOPLASM Proteins Hydrophilic heads Cytoskeleton Proteins Cell membrane Hydrophobic tails Protein with channel

LE 3-5 EXTRACELLULAR FLUID Lipid-soluble molecules, O 2 and CO 2 diffuse through membrane lipids. Plasma membrane Channel protein Large molecules that cannot diffuse through lipids cannot cross the membrane unless they are transported by a carrier mechanism CYTOPLASM Small water-soluble molecules and ions diffuse through membrane channels

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 H 2 O, 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 Water molecules Glucose molecules AB 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 Volume decreased 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. Volume increased

Diffusion & Osmosis Animations

LE 3-7a Isotonic Water molecules

LE 3-7b Water molecules Hyp0tonic

LE 3-7c Hypertonic Solute molecules Hypertonic

LE 3-8 Glucose molecule attaches to receptor site EXTRACELLULAR FLUID CYTOPLASM Receptor site Carrier protein Change in shape of carrier protein Glucose released into cytoplasm

LE 3-9 EXTRACELLULAR FLUID CYTOPLASM Sodium– potassium exchange pump 3 Na + 2 K + ATP ADP

LE 3-10 EXTRACELLULAR FLUID Ligands binding to receptors Exocytosis Ligand receptors CYTOPLASM Coated vesicle Ligands Endocytosis Fusion Lysosome Fused vesicle and lysosome Ligands removed Detachment

LE 3-11 EXTRACELLULAR FLUID Pseudopodium (cytoplasmic extension) Foreign object Vesicle CYTOPLASM Undissolved residue Lysosomes Cell membrane of phagocytic cell

LE 3-12 Microvillus Microfilaments Cell membrane Mitochondrion Intermediate filaments Endoplasmic reticulum Secretory vesicle Microtubule

LE 3-14a Endoplasmic reticulum Transport vesicle Golgi apparatus Membrane renewal vesicles Secretory vesicles Lysosomes CYTOSOL Vesicle incorporation in cell membrane Cell membrane EXTRACELLULAR FLUID

LE 3-14b Exocytosis

Transport Types Animations /animations/membrane_transport/me mbrane_transport.htmhttp:// /animations/membrane_transport/me mbrane_transport.htm