Biology 171 Lab Report

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.