Download Effects of Alcohol Concentration on Beet Membranes--Pre

Effects of Alcohol on Membranes—Pre-Lab
The primary objective of this experiment is to determine the stress that ethanol (the alcohol people drink),
methanol, and l-propanol have on biological membranes. Membranes within cells are composed mainly
of lipids and proteins and often serve to help maintain order within a cell by containing cellular materials.
Different membranes have a variety of specific functions.
One type of membrane-bound vacuole found in plant cells, the tonoplast, is quite large and usually
contains water. In beet plants, this membrane-bound vacuole also contains a water-soluble red pigment,
betacyanin. Since the pigment is water soluble and not lipid soluble, it remains in the vacuole when the
cells are healthy. If the integrity of a membrane is disrupted, however, the contents of the vacuole will
spill out into the surrounding environment. This usually means the cell is dead.
In this experiment, you will test the effect of the alcohols on cell membranes. Ethanol is found in
alcoholic beverages. Methanol, sometimes referred to as wood alcohol, can cause blindess and death.
Propanol is fatal if consumed. One possible reason why they are so dangerous to living organisms is that
they might damage cellular membranes. They are all similar alcohols, differeing by the number of carbon
and hydrogen atoms within the molecule. Methanol, CH3OH, is the smallest; ethanol CH3CH2OH, is
intermediate in size, and l-propanol, CH3CH2CH2OH, is the largest of the three molecules.
Background Neuronal Membranes
The neuronal membrane serves as a barrier to enclose the cytoplasm inside the neuron, and to
exclude certain substances that float in the fluid that bathes the neuron.
The membrane with its mosaic of proteins is responsible for many important functions:
* keeping certain ions and small molecules out of the cell and letting others in,
* accumulating nutrients, and rejecting harmful substances,
* catalyzing enzymatic reactions,
* establishing an electrical potential inside the cell,
* conducting an impulse
* being sensitive to particular neurotransmitters and modulators .
The membrane is made of lipids and proteins - fats and chains of aminoacids. The basic structure of this
membrane is a bilayer or sandwich of phospholipids, organized in such a way that the polar (charged)
regions face outward and the non polar regions face inward.
The external face of the membrane contains the receptors, small specialized molecular regions which
provide a kind of "attachment port" for other external molecules, in a scheme analogous to a a key and a
keyhole. For each external molecule there is a corresponding receptor. Whenever receptors become
attached to a molecule, some alterations of the membrane and in the interior of the cell ensue, such as the
modification of permeability to some ions.
Dendrites
These structures branch out in treelike fashion and serve as the main apparatus for receiving
signals from other nerve cells. They function as an "antennae" of the neuron and are covered by thousands
of synapses. The dendritic membrane under the synapse (the post-synaptic membrane) has many
specialized protein molecules called receptors that detect the neurotransmitters in the synaptic cleft. A
nerve cell can have many dendrites which branch many times, their surface is irregular and covered in
dendritic spines which are where the synaptic input connections are made.
Alcohol Kills Brain Cells
Just one observation of a drunken person is enough to convince you that alcohol directly affects
the brain. People who drink enough to get drunk often end up with slurred speech and impaired motor
skills and judgment, among other side effects. Many of them suffer from headaches, nausea and other
unpleasant side effects afterward -- in other words, a hangover. But are a few drinks on the weekend, or
even the occasional long drinking session, enough to kill brain cells? What about binge drinking or the
frequent, sustained drinking of alcoholics?
Not so much. Even in alcoholics, alcohol use doesn't actually result in the death of brain cells. It
can, however, damage the ends of neurons, which are called dendrites. This results in problems conveying
messages between the neurons. The cell itself isn't damaged, but the way that it communicates with others
is altered. According to researchers such as Roberta J. Pentney, professor of anatomy and cell biology at
the University at Buffalo, this damage is mostly reversible.
Doing the Lab
So if a beet membrane is damaged, the red pigment will leak out into the surrounding environment. The
intensity of color in the environment should be proportional to the amount of cellular damage sustained
by the beet.
To measure the color intensity, you will be using a colorimeter. In this device, blue light from the LED
light source will pass through the solution and strike a photocell. The alcohol solutions used in this
experiment are clear. IF the beet pigment leaks into the solution, it will color the solution red. A higher
concentration of colored solution absorbs more light and transmits less light than a solution of lower
concentration. The colorimeter used here will produce a percent absorption number.
You are going to prepare 5 solutions of differing concentrations. You will put a piece of each beet in
each alcohol in each concentration and wait 10 minutes for the alcohol to work. You will then pull the
red solution from the beaker and put it into a cuvette and then into the colorimeter where you will record
the percent absorption.
Pre-Lab Questions:
1.) Draw the Lewis Structures of ethanol, methanol, and l-propanol.
2.) Which alcohol will do the most damage to the beet? Why?
3.) How can you determine which does the most damage?
4.) What is the difference between absorption and transmittance? Write a mathematical sentence
involving both using A for absorption and T for transmittance.
5.) How does alcohol affect dendritic membranes/ neurons and thus your brain?
6.) Time for this lab is short and you will only have one period. Get into your groups for the lab. Write
out in detail who is going to do what part of the lab—in other words, assign specific tasks to each person
in your group. The purpose for this question is to save time tomorrow in the lab.