Biol 171L
The effects
that various alcohols and amphiphilic substances have on beet cell membranes
An experiment was
done to discover the effects that various alcohols in different concentrations
and an amphiphilic substance, sodium dodecyl sulfate (SDS), has on beet cell
phospholipid membranes. This is important to know because the process in which
damage may or may not occur to a cell membrane in a certain solution such as
alcohol could then be explained with better understanding. The way that the
results were obtained was through measuring the amount of betacyanin that was
released from the beet cells into the solution through spectrophotometry. The
spectrophotometer measured the absorbance of color and light, altered by the
beet pigments, in each solution. The findings were that as the concentrations
of each alcohol were raised, the amount of pigment absorbance readings rose,
and as the concentration of SDS rose in the solutions, the absorbance readings
also rose. Therefore, it was concluded that there was more damage to the beet
cells when placed in higher concentrations of alcohol. The most damage from the
alcohols was done by the 1-Propanol, it is a possibility that this is because
of the non-polarity and amphipathic nature of the alcohol. Also, as the
concentration of SDS was raised, the absorbance measurements rose also, and it
was concluded that perhaps this is because SDS is an amphiphilic detergent
which dissociates a cells phospholipid membrane when it comes into contact with
it.
The procedure
began with first cutting twenty uniform beet discs to place one in each
solution for measurement of released pigment. A piece of beet was placed in
five different concentrations, ranging from 0% to 50%, of three alcohols;
Methanol, Ethanol, and 1-Propanol. After 10 minutes of waiting and gently
mixing, the beet samples were extracted from the wells and the solutions were
transferred into a cuvette which was placed in the spectrophotometer for
absorbance measurement. The machine was first calibrated, the wavelength was set
at 470 nm, and it was blanked. The absorbance readings of betacyanin in each
solution were measured by the machine, and the measurements varied throughout
the three alcohols (see Table 1).
Table 1: The Class
Average Absorbance readings of betacyanin in various alcohols
Concentration (%)
|
Methanol
|
Ethanol
|
1-Propanol
|
0
|
.086
|
.110
|
.128
|
10
|
.100
|
.107
|
.165
|
20
|
.111
|
.112
|
.505
|
30
|
.118
|
.293
|
.590
|
40
|
.189
|
.334
|
.474
|
It
can be seen through the absorbance readings that there was more of the red
pigment released from the cell into the solution as the concentration of the
alcohol rose, with the exception of 1-Propanol. There was a very similar trend
seen in the absorbance readings of the SDS solutions. As the concentration of
sodium dodecyl sulfate was increased, the absorbance measurements also rose
(see Table 2).
Table
2: The class average absorbance readings of betacyanin in different
concentrations of SDS
Concentration (%)
|
Absorbance Readings
|
0
|
.114
|
0.1
|
.228
|
0.2
|
.420
|
0.3
|
.538
|
0.4
|
.585
|
It’s
possible that the reason why the pigment absorbance measurements were getting
higher with each concentration increase of SDS is because sodium dodecyl
sulfate and the phospholipids of the membrane are amphipathic. When amphipathic
substances mix with one another, the membrane will be dissociated because both
the phospholipids and the SDS detergent have a hydrophilic and a hydrophobic
region on different sides.
When
the absorbance was measured in the alcohol solutions, the measurements also
rose as the concentration increased. It is possible that this is because
alcohols are typically polar, but the more carbons present by having a higher
concentration decreases the polarity from being polar, to amphiphilic, to
non-polar. Due to its polar and/or nonpolar properties, alcohols usually can
get through the cell membrane and destroy the fluidity, causing the red
pigment, betacyanin, to leak out of the beet cell. In the case of 1-Propanol,
it is the larger molecule, and the larger the molecule, the more damage to the
membrane. 1-Propanol, a three carbon molecule, is larger than ethanol, a two
carbon molecule and methanol, a one carbon molecule. Lipids can be composed of
hydrocarbon chains, which are non-polar. As alcohol increases in length, it
becomes less polar than smaller alcohols, and are able to mix with lipids better.
Since the hydroxyl branch mixes with water, the longer alcohols can mix with
both lipids and water. This dissociates the membrane just like detergents and
soaps do. Therefore, larger alcohols usually cause more extensive damage to a
cell membrane.
To
apply this concept to day to day life, it is recognized that lab classes
generally use 70% ethanol solutions to clean the bench areas after experiments.
This is probably because 70% is a tough enough concentration to lead to the
breakdown of the cellular membranes of bacteria, which would then denature
proteins and kill bacteria. This concentration has been shown to have the
highest killing capability of microbes. But many organisms have a cell wall which
consist of proteins and carbohydrates that are not dissolved by ethanol. When the
alcohol is mixed with water, the ethanol can reach the lipid layers and the
cells can be killed. 70% ethanol solutions are is the concentration that proved
to be most effective against microbes; as a result, the 70% are used. If 100%
ethanol was used, it would be very toxic and a greater hazard to the user.
Although the 70% ethanol solutions kill most bacteria on surfaces, it is still
advised to wash hands with soap afterwards to get rid of any lingering microbes
on hands.
To
conclude, by exposing a cell to a solvent such as alcohol, it will affect the permeability
of the cell membrane. The higher the concentration of the solvent, the more
permeable the membrane will be. From the results, it can be clearly seen that
at 40% concentration of each alcohol, the cell membrane of the beet cells were
broken down the most, except for 1-Propanol, probably because it was reaching a
non-polar state instead of amphiphilic due to all the carbon atoms present. As
for the amphiphilic detergent, sodium dodecyl sulfate, it has similar
components of cellular membranes. Detergents have hydrophobic properties because
of their non-polar tails. However, detergents are also water-soluble because
they have hydrophilic properties due to their polar heads. So, amphiphilic detergent
molecules cause the spreading of water-insoluble, hydrophobic compounds into watery
solutions. This leads to the dissociation of the phospholipid bilayer of cell
membranes, which then (in a beet cell case) would cause the red pigment,
betacyanin, to be released from the cell, showing that there was indeed
membrane damage to the cell.
