Cellular Transport Or- How do I get in and out of here?

Cells need to: Move nutrients into the cell Remove waste products from the cell Export products made for other parts of the organism (hormones, enzymes, neurotransmitters, etc.) Control the concentration of materials inside the cell.

The Cell Membrane: Controls what enters and leaves the cell Is Semi permeable – allows some molecules to move freely through, but keeps others out

Three Ways to Move In/Out of a Cell: Passive Transport Active Transport Bulk Transport

Passive Transport The cell does not need to use any energy Movement of materials is from an area of high concentration to an area of low concentration (molecules spread out) Molecules move with the concentration gradient High Low

Passive Transport - Diffusion Movement : Occurs until equilibrium is achieved Caused by random motion of molecules Diffusion is Affected by : Temperature Faster at higher temperatures Molecular weight Lighter molecules move faster Concentration gradient Faster when gradient is high

Can diffusion happen through the cell membrane? YES, as long as the particles are small enough and not charged

Small, non charged molecules and water can move between the phospholipid molecules of the membrane. This includes: carbon dioxide, oxygen, alcohol, glycerol

Passive Transport: Facilitated Diffusion Substances helped into the cell by channel proteins –Polar molecules such as glucose –Ionic molecules such as amino acids Still does not use any cellular energy. Transport Protein

Diffusion vs. Facilitate Diffusion

What happens when the particles are too big to cross the membrane and there are no protein channels? Large Molecules Water Moves osmosis

Passive Transport: Osmosis The movement of WATER across a differentially permeable membrane –Solutes can not move across membrane but water can –Water moves from an area of high water concentration to low water concentration –Water diffuses towards the higher concentration of solute.

Three Concentration Situations: Isotonic: a solution that has an equal solute concentration to a neighboring solution. Hypertonic: a solution that has a relatively higher solute concentration. Hypotonic: a solution that has a relative lower solute concentration.

Water moves towards the higher solute concentration:

What does this mean to a cell? The water content of the cell will be affected by the concentration of solutes around and in the cell.

HypertonicIsotonic Hypotonic Plasmolysis occurs – cell shrinks as water leaves Water enters the cell. If too much water enters the cell will burst No net movement of water in or out of cell

Plants have a cell wall to protect from bursting. Vegetables are crisp when they hold a lot of water and wilt when they lose it.

Active Transport

Active Transport: Energy Required Transport protein uses energy (ATP) to change shape Transport protein able to move molecule in or out of cell Molecule is moved to increase the concentration gradient Transports against the concentration gradient (low to high)

Active Transport: Nerve Cells

Bulk Transport Macromolecules are too large to move with membrane proteins and must be transported across membranes in vesicles. The transport of macromolecules out of a cell in a vesicle is called exocytosis. The transport of macromolecules into a cell in a vesicle is called endocytosis.

Exocytosis – molecules leave the cell when the vesicle fuses with the membrane Endocytosis – molecules brought into the cell by infolding the membrane and forming a vesicle

Bulk Transport If the material taken up by endocytosis is a large particle it is called phagocytosis. If the material taken up by endocytosis is a liquid or small particle it is called pinocytosis. Receptor-mediated endocytosis is a selective, highly efficient form of endocytosis.

Bulk Transport: Receptor Mediated Receptor attaches to a specific molecule and moves it into the cell