Warm-Up 11. Is the plasma membrane

symmetrical? Why or why not?2. What types of substances cross the

membrane the fastest? Why?3. Explain the concept of water

potential. (Hint: Refer to Lab 1)

Warm-Up 21. What are glycoproteins and

glycolipids and what is their function?

2. How do hydrophilic substances cross the cell membrane?

3. Why does water move through the bi-layer quickly?

Warm-Up 31. Side A in a U tube has 5M sucrose and 3

M glucose. Side B has 2 M sucrose and 1 M glucose. The membrane is permeable to glucose and water only. What happens to each side?

Warm-Up 41. Side A in a U tube has 3 M sucrose and 1

M glucose. Side B has 1 M sucrose and 3 M glucose. The membrane is permeable to glucose and water only. What happens to each side?

Cell Transport NOTESGrowth and dynamic homeostasis are maintained by the

constant movement of molecules across membranes.

Passive TransportNO ENERGY needed!Diffusion down concentration gradientconcentration gradient (high low

concentration)Eg. hydrocarbons, CO2, O2, H2O

Importance:IMPORT of RESOURCES (nutrients, O2, H2O, etc.)EXPORT of WASTES (CO2, etc.)

Facilitated DiffusionTransport proteinsTransport proteins (channel or carrier proteins) help

hydrophilic or charged substance cross• (1) Provide hydrophilic channel

or (2) loosely bind/carry molecule across

• Eg. ions, polar molecules (glucose)

Active TransportWhere free energy is used by proteins

embedded in membrane to MOVE molecules and / or ions to maintain homeostasis

Requires ENERGYENERGY (ATP)Proteins transport substances against

concentration gradientconcentration gradient (low high conc.)

Eg. Na+K+ pumps, proton pumps, endocytosis, exocytosis

Electrogenic Pumps: generate voltage across membraneNa+/K+ Pump Proton PumpPump Na+ out, K+ into

cellNerve transmission

Push protons (H+) across membrane

Eg. mitochondria (ATP production)

Cotransport: membrane protein enables “downhill” diffusion of one solute to drive “uphill” transport of other

Eg. sucrose-H+ cotransporter (sugar-loading in plants)

Passive vs. Active TransportLittle or no EnergyHigh low

concentrationsDOWN the

concentration gradient

eg. diffusion, osmosis, facilitated diffusion (w/transport protein)

Requires Energy (ATP)

Low high concentrations

AGAINST the concentration gradient

eg. pumps, exo/endocytosis

Bulk TransportTransport of proteins, polysaccharides, large molecules, etc.

from the external environment to the internal (and vice versa)

Endocytosis: take in macromolecules, form new vesicles

Exocytosis: vesicles fuse with cell membrane, expel contents

EndocytosisCell takes in macromolecules and particulate matter by

forming new vesicles derived from the plasma membrane

Phagocytosis:“cellular eating” - solids

Pinocytosis:“cellular drinking” - fluids

Receptor-Mediated Endocytosis:Ligands bind to specific receptors on cell surface

ExocytosisInternal vesicles fuse with the plasma membrane to

secrete large macromolecules out of the cell.

Internal MembranesEukaryotic cells maintain internal membranes that

partition the cell into specialized regions

Functions:Minimize competing interactionsIncreased surface area where reactions can occurIsolate specific enzymatic reactions

Organelles with internal membranes:Endoplasmic ReticulumMitochondriaChloroplastsGolgiNuclear Envelope

Archaea and BacteriaLack internal membranesHave a cell wall