Sunday, September 19, 2010

May the Force be with You!

So we discussed passive transport on Thursday!

Those processed require no energy or special accommodation, but that is not always the case when it comes to moving substances across the plasma membrane.

Even when no energy is required, sometimes a particle is too big to wiggle through the phospholipids and must take an alternate route.  Membrane proteins that span the entire bilayer provide passage ways for larger molecules to pass through without exertion of energy.  Using a protein to pass through the membrane is known as facilitated diffusion.

However sometimes particles need to enter a cell that are too large to even use a membrane protein or they are trying to go against the concentration gradient (from L to H).  Transport that requires energy is known as active transport.

When the cell brings in a large particle or expels one, they can use the membrane to form a vesicle around the object.

Exocytosis: uses the membrane to spit objects out of the cell.

Endocytosis: the membrane encloses items to bring them into the cell.

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