Re: how does ethanol effect plasma membranes

Hi Jennie,

So I see that you are most likely extracting pigments from beet root and 
using ethanol to disrupt membranes? If not, its a fun experiment.

Ethanol disrupts membranes by a number of methods. In particular what you 
must remember is, the size and fluidity of the membrane has a lot to do 
with the outside and inside environment. This environment consists of how 
much water, salts etc are in the cell versus out of the cell.  Adding 
ethanol disrupts much of this.

1. Ethanol is permeable to cell membranes.  Because of the nature of 
ethanol as a chemical is it able to get into the cell very easily. This 
disrupts the balance of the cells' osmotic environment. Osmosis is the 
movement of water. Think about what happens if you fill a balloon too 
full. What happens? It expands and stretches the membrane of the balloon. 
If you release too much water from the balloon it crumples the membrane 
and deflates, no longer keeping it structure.  This is the same in a 
cell. Ethanol disrupts this flow.  It has also been shown that ethanol 
can disrupt the ion channels in the plasma membrane. These channels in 
the cell membrane help pump ions like calcium and potassium in and out of 
the cell which directly control how much water is pumped in and out of 
the cell (remember the balloon). 

2. Ethanol disrupts water. What I mean by this is that ethanol has the 
ability to make hygrogen bonds. These are the weak, yet plentiful, bonds 
a hydrogen atom can make with a negative atom like oxygen or nitrogen. If 
you don't remember hygrogen bonds, please look them up. They are not 
ionic bonds nor covalent bonds, but rather weak attractive forces between 
hydrogen and a semi-negative charged oxygen or nitrogen.  Hydrogen bonds 
are one of the major reasons we have life on earth. Hydrogen bonds give 
water its properties including how water molecules organize themselves.  
Ethanol get inbetween these water molecules and disrupts their 
organization.  And yes, liquid water is an organized fluid. Not quite as 
organized as frozen water (ice) but organized none the less.  When 
ethanol disrupts this organization, it too can also disrupt how the 
hydrophilic (water loving) regions of the plasma membrane interacts with 
the water.

Disrupting these interactions can change the structure of the membranes. 
Put that together with an environment where ethanol is also messing up 
the proper flow of ions and water and you have an instable environment.

This is enough to break the membranes open and in many cases, dehydrate 
the cells.

If you are extracting pigments, ethanol is also the perfect solute for 
pigments and therefore helps in the extraction process.

I hope this helps!

Matt