The Cell as the Fundamental Unit of Life: Membrane Transport Processes

Fluid mosaic model: Working model of the membrane Protein molecules bobbing in phospholipid sea Proteins determine membrane’s specific functions

Phospholipids Most abundant lipid Polar/hydrophilic head(attracted to water) Pair of nonpolar/hydrophobic tails(repelled by water) Hydrophilic head Hydrophobic tails

Polar heads, outside & inside Nonpolar tails in the interior cell membranes Hydrophilic head phospholipid Hydrophilic head Hydrophobic tail outside inside

Microvilli- intestinal cells Membrane Junctions Tight junctionsDesmosomesGap junctions

Selectively permeable- allows certain substances to pass through By 2 ways: active or passive transport Passive- downhill Active- uphill (needs energy)

Passive: downhill reaction Simple diffusion Osmosis Facilitated diffusion Filtration Active: uphill reaction, needs ATP Exocytosis Endocytosis - Pinocytosis - Phagosytosis

No Barrier: Substances “spread out” High concentration to low concentration e.g.: Red dye placed in glass of water

Substances diffuse High concentration to low concentration Pores in membrane must be large “Down the concentration gradient” Dynamic equilibrium, equal rates in both directions Biological membrane:

Carrier proteins: Bind specific molecule & change shape Pass molecule through middle of protein

Osmosis- diffusion of a water through a semi- permeable membrane Moves down concentration gradient e.g., Two sugar solutions of different concentrations separated by porous membrane which lets water through but not sugar What will happen?

More concentrated to less concentrated Until concentration same on both sides: isotonic

Concentration of solute less: solution is hypotonic. Concentration of solute greater: solution is hypertonic.

Animal cells No cell walls Isotonic environment: Influx of water equals the efflux of water No change in cell shape

Hypotonic solution: Water enters cell Bursts, or lyses Hypertonic solution: Water leaves cell Shriveled, or crenate

Glomerular filtration

Passive Transport and Facilitated Diffusion Passive transport & facilitated diffusion do NOT require ATP

Active Transport DOES require the input of ATP Transport proteins AGAINST concentration gradient outside cell inside cell

ATP  ADP + P i + Energy

mucus Goblet cell

Membrane Permeability Cell membrane:  selectively permeable 4 factors that determine permeability lipid solubility molecular size polarity charge

Lipid solubility Most important factor Hydrophobic molecules Passively diffuse Hydrocarbons, carbon dioxide, & oxygen

Molecular Size and Polarity Larger molecules, less permeable Lower kinetic energy Small pore sizes in the membrane Polar molecules hydrophilic, less permeable Very small, polar uncharged (water) molecules can diffuse - + Molecular Size Polarity

Charge Charged molecules hydrophilic, less permeable Surrounded by coat of water (hydration shell), increases the size

INQUIRY 1.What is the main difference between active transport and facilitate diffusion? 2.In osmosis, water moves from a xxxx solution to a xxxx solution. 3.What happens to blood cells placed in pure water? 4.Which portion of the phospholipid molecule faces the environment outside of the cell? 5.The release of insulin from certain human cells is an example of xxxx(endo, exo, phago, pinocytosis).