How does acid affect the cell membrane

Of all the amazing technologies humans have developed, none has matched the complexity of the fundamental building block of nature: the living cell. And none of the cell's activities would be possible without thin lipid membranes, or bilayers,that separate its parts and regulate their functions.

Changes in the packing of the tails into a hexagonal, rectangular-C, or rectangular-P lattice are observed at various pH levels.

Understanding and controlling bilayers' properties is vital for advances in biology and biotechnology. Now an interdisciplinary team of Northwestern University researchers has determined how to control bilayers' crystallization by altering the acidity of their surroundings.

The research, published September 24 in the Proceedings of the National Academy of Sciences, sheds light on cell function and could enable advances in drug delivery and bio-inspired technology.

"In nature, living things function at a delicate balance: acidity, temperature, all its surroundings must be within specific limits, or they die," said co-author Monica Olvera de la Cruz, Lawyer Taylor Professor of Materials Science and Engineering, Chemistry, and (by courtesy) Chemical and Biological Engineering at Northwestern's McCormick School of Engineering. "When living things can adapt, however, they are more functional. We wanted to find the specific set of conditions under which bilayers, which control so much of the cell, can morph in nature."The research, published September 24 in the Proceedings of the National Academy of Sciences, sheds light on cell function and could enable advances in drug delivery and bio-inspired technology.Understanding and controlling bilayers' properties is vital for advances in biology and biotechnology. Now an interdisciplinary team of Northwestern University researchers has determined how to control bilayers' crystallization by altering the acidity of their surroundings.

By taking advantage of the charge in the molecules' head groups, the Northwestern researchers developed a new way to modify the membrane's physical properties. They began by co-assembling dilysine (+2) and carboxylate (-1) amphiphile molecules of varying tail lengths into bilayer membranes at different pH levels, which changed the effective charge of the heads. Bilayers are made of two layers of amphiphile molecules -- molecules with both water-loving and water-hating properties -- that form a crystalline shell around its contents. Shaped like a lollipop, amphiphile molecules possess a charged, water-loving (hydrophilic) head and a water-repelling (hydrophobic) tail; the molecules forming each layer line up tail-to-tail with the heads forming the exterior of the membrane. The density and arrangement of the molecules determine the membrane's porosity, strength, and other properties.

Then, using x-ray scattering technology at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) at Argonne National Laboratory's Advanced Photon Source, the researchers analyzed the resulting crystallization formed by the bilayers' molecules.

(To produce electron microscope images of membrane structures, researchers previously have frozen them, but this process is labor-intensive and changes the structural fidelity, which makes it less relevant for understanding membrane assembly and behavior under physiological conditions as carried out inside the human body.)

The Northwestern researchers found that most molecules did not respond to a change in acidity. But those that possessed a critical tail length -- a measure that correlates to the molecules' level of hydrophylia -- the charge of the molecules' heads changed to the extent that their two-dimensional crystallization morphed from a periodic rectangular-patterned lattice (found in more basic solutions) to a hexagonal lattice (found in more acidic solutions). Shells with a higher symmetry, such as hexagonal, are stronger and less brittle than those with lesser symmetry. The change in pH also altered the bilayers' thickness and the compactness of the molecules.

Changing the density and spacing of molecules within membranes could help researchers control the encapsulation and release efficiency of molecules inside a vesicle.

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Materials provided by Northwestern University. Note: Content may be edited for style and length.

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AS BIOLOGY COURSEWORK The aim of this experiment is to see what effect the concentration of acid has on damaging the cell membrane of red cabbage, causing the pigment to leak. The hypothesis to be tested is that the higher the concentration of the acid the larger the extent of the damage to the cell membrane. This theory is likely to be proven because pH is known to damage plasma bilayers. Red Cabbage Red cabbage is coloured dark red-purple due to a pigment called anthocyanin. The colour of the pigment changes according to the pH value of the soil. The pigment can be used as a pH indicator, turning red in acid and blue in alkaline solutions. I will be investigating how acid damages the cell membrane. It is difficult for acids to cross the cell membrane without damaging the membrane, and as acid is not a substance that is taken in naturally by the plant it is likely to have an effect on the integrity of the membrane. It could be suggested that the higher the concentration of acid, the more pigment will be released as the membrane becomes more damaged. This will cause the solution the cabbage is in to darken to the colour of the pigment, and so less light can be transmitted, or more light absorbed through the solution. I can therefore measure the amount of damage to the cell membrane by measuring the amount of light that is absorbed or can be transmitted through the solution. The cell membrane, also called the plasma membrane is a semi permeable liquid bilayer found in all cells. Its primary function is to control what enters and exits the cell, and so facilitates the transport of materials needed by the cell. It also has other functions, such as acting as a boundary between the cytoplasm and outside the cell and, to a limited extent, provides support to the cell. ...read more.

used 10cm� HCl, 10cm� water * 0.4 molar used 8cm� HCl, 12cm� water * 0.3 molar used 6cm� HCl, 14cm� water * 0.2 molar used 4cm� HCl, 16cm� water * 0.1 molar used 2cm� HCl, 18cm� water 4. Add 10 discs of cabbage into each boiling tube and leave for 1 hour. 5. After 1 hour, collect the solutions off the cabbage pieces. In order to produce a control colorimeter reading, use a cuvette filled with pure HCl to get a reading of 0.00. 6. Using a pipette, transfer the solutions into the cuvettes and place in the colorimeter. 7. Ensure the colorimeter is recording the absorption of blue light, (frequency 470). 8. Repeat the experiment three times to ensure accuracy and reliability in the experiment. Safety: * Standard laboratory safety followed - CLEAPSS for strong concentrations of acid * contact with skin and eyes can cause damage and irritation- if contact occurs flush with water and remove any contaminated clothing. If swallowed drink plenty of water. Seek medical advice. * Concentrated solutions are extremely corrosive, dilute concentrations are mildly corrosive * Toxic when inhaled - hydrogen chloride vapour given off * If diluted and flushed with sufficient water, HCl will not damage the natural environment. As precaution, wear safety glasses when handling hydrochloric acid. Gloves could be used to protect against contact with the skin. The acid is best used in a well ventilated area. * As a food plant, cabbage is not dangerous. * Plant material - i.e. no sentient organisms involved * No relevance of wild material Results Here is my data collectively shown, using arbitrary units. Acid Molarity (m) Colorimeter Reading (Absorption) (Arbitrary units) Average Colorimeter Reading (arbitrary units) Percentage Absorption (%) 1 2 3 0.1 0.26 0.12 0.22 0.20 10.00 0.2 0.30 0.24 0.49 0.36 18.00 0.3 0.50 0.35 0.46 0.44 22.00 0.4 0.53 0.37 0.57 0.49 24.50 0.5 0.38 0.38 0.60 0.45 22.50 0.6 0.40 0.41 0.73 0.51 25.50 0.7 0.53 0.41 0.74 0.56 28.00 0.8 0.62 0.43 ...read more.

If there is a variation in the results, it is likely to be within the threshold range, where most of the damage is taking place. The main difficulty with my experiment was collecting enough cabbage discs of equal size to give me adequate results. I needed to take the discs from the same leaf of the cabbage to ensure accuracy, and this process was time consuming and delicate. However, my data gave me a clear sigmoid shaped curve with results that can be explained my hypothesis and research. I am therefore confident in my methodology, because my results enabled me to prove my hypothesis. I could perhaps have taken more repeat readings which would have minimised any slight anomalies, but I felt that taking eight orders of magnitude and repeating three times was more useful and valid than say, five orders of magnitude repeated five times, and indeed more practical in the time allowed. Further Work If I was to extent my research, I could firstly take more repeats to ensure the accuracy and reliability of my results. I could also perform a series of these experiments, but from different parts of the cabbage, for example discs from different leaves to give me more varied data to reach my conclusion from. I could also carry out a similar experiment using beetroot and other naturally pigmented plants, to see if the damage to the cell membrane is comparable with other plants and therefore representative for all plant cell membranes. The key region, of the threshold range, i.e. where most of the damage takes place and leakage is at a maximum, i.e. between 0.0001 and 0.1 molar, could be investigated further, firstly by taking more readings within that range. After having damaged the membrane and obtained leakage, it might be interesting to see with appropriate microscopy (including electron microscopy) if there are notable differences in the structure of the cell membrane at different acidities, for example, simply a different physical appearance. Sophie Keltie Page 1 of 11 ...read more.

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