Traffic Across Membranes

Factors that Affect the Transport of Molecules Across a MembraneCharge of the molecule (cation-positive AND anion-negative)Size of the pores/holes in the membraneConcentration of molecules inside and outside the cellTemperatureAvailable proteins

Passive Transport (three types)

No work or energy is required (spontaneous)Molecules move down its concentration gradient (i.e. From an area of high concentration to low an area of low concentration)Continuous movement (even after there are equal concentrations of solutes on both sides of the membrane)

1. Diffusion-movement of molecules from an area of high concentration to an area of lower concentration. diffusion demo

2. Osmosis- diffusion of water molecules from an area of high concentration to an area of lower concentration.

3. Facilitated Diffusion diffusion of polar molecules and ions with the help of transport proteins.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

facilitated diffusion

Passive transport is like rolling down a hill...happens naturally/no energy

Active Transport (two types)

Pumping of solutes against their concentration gradient. Solutes move from an area of low concentration to an area of high concentration “uphill”Requires work/energyUses proteins

1. Exocytosis- movement of molecules outside a cell using vesicles.

2. Endocytosis-cell takes in macromolecules, creating new vesicles.

a.) Phagocytosis-cell engulfs a particle and forms a vesicle- “cell eating”

-vesicle fuses with a lysosome creating a phagolysosome which breaks down the contents

phagocytosis

b.) Pinocytosis-cell engulfs extracellular fluid in tiny vesicles- “cell drinking” (not specific)

c.) Receptor-mediated endocytosis- very specific and in clusters to take in bulk amount of a certain type of molecule.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis

pino and phagohttp://www.youtube.com/watch?

v=InG6xF9D4EM

Tonicity (osmosis)Osmoregulation- control of water balance.

*Balancing the water between a cell and its environment is crucial for cell survival. Types of Solutions:

I. Hypertonic Solution-solution with a high solute concentration.

II.Hypotonic Solution-solution with a low solute concentration.

III.Isotonic- same amount of solute on both sides of the cell membrane.

Turgid-very firmFlaccid-limp/wilts

Plasmolysis-cell membrane pulls away from the cell wall.

Hypo Hyper Isotonic

osmosis

http://student.ccbcmd.edu/~gkaiser/TOC/images/osmosis_hyper.htmlhttp://student.ccbcmd.edu/~gkaiser/TOC/images/osmosis_hypo.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://www.youtube.com/watch?v=InG6xF9D4EM