Chemical Composition of Cell Membranes

Chemical Composition of Cell Membranes and Factors Affecting Permeability Each eukaryotic cell has a complex membrane system, whose general role is to regulate the exchange of materials between the cell and its surrounding environment and between cell organelles. In the membrane system, cellular metabolic reactions also take place. The plasma membrane or plasmalemma of a higher plant cell is the outer boundary of the protoplasm that faces the cell wall. The tonoplast or vacuole membrane, encloses the vacuole and separates it from the cytoplasm (in mature higher plant cells there is usually only one large vacuole). Organelles such as chloroplasts, mitochondria, endoplasmatic reticulum, perixisomes and others are protected by membranes. Chloroplasts and mitochondria have two membrane layers, where the inner membrane shows a complicated organization. Based on the ultrastructure and function of the membrane, it is proven that the membrane is composed of protein and fat which has a three-layer structure with a thickness of approximately 75 Angstroms. Based on Davson and Danielli's hypothetical model, the protein layer flanks a bimolecular layer of fat (phospholipid). Another special property of membranes besides their chemical composition is their semipermeable (differential permeable) functional properties. Water passes through the membrane passively based on a water potential gradient. Some solutes can pass but with different speeds and mechanisms. In non-living membranes, the difference in permeability depends on the size of the molecules that want to pass through and is also determined by the size of the membrane pores. But in the plasma membrane (living cells) the size of the molecule has no effect. This is thought to be related to the solubility of the substance in one of the membrane components. So the membrane is not just a passive layer. We will see this in the following experiment. Experiment a. Effect of Temperature and Chemical Compounds on Cell Membrane Permeability Objective: Looking at the effect of various physical and chemical treatments on membrane permeability. Materials and tools : Plant material : tubers of a type of root crop Chemical material : distilled water, methanol, acetone and tertiary butyl alcohol Tools : 1000 ml beaker, drill to make shaped pieces cylinder with a diameter of 1 cm, spectrophotometer and cuvette, thermometer,freezer , test tubes, and razor blades. Ways of working: 1. Choose a large potato tuber, wash it thoroughly with tap water if necessary, brush it. 2. With the help of a drill with a diameter of 1 cm (hole in the middle), cut 12 cylindrical shapes from the same tuber if possible. 3. Cut the cylinder shape with a thickness of 3 cm. 4. Wash all the tuber pieces under running water (tap water) for 10-15 minutes to remove the pigment on the surface. a. Heat treatment 1. Prepare a water bath by filling 2/3 of a 1000 ml beaker with water, and heat it over a fire orhot plates . 2. With tweezers or a long needle, put the cut potato tubers into a beaker that has been heated to a temperature of 70oC (place the thermometer in a beaker) for 1 minute. 3. Then transfer the cut potato tubers from the beaker into a test tube containing 15 ml of water at room temperature 4. Let the water in the beaker gradually cool, then add the cut potato tubers one piece at a temperature of 65oC, 60oC, 50oC, 45oC (can be read on a thermometer) for 1 minute. 5. As in point A1, transfer the potato tuber pieces soaked in hot water into a test tube containing distilled water at room temperature. As a control, place one potato tuber in a tube containing 15 ml of distilled water. 6. After incubating for 1 hour, shake the test tube and pour the mixture into a cuvette and measure the absorbance at a wavelength of 525 nm on a spectrophotometer. 7. Perform point A6 for each soaking water (7 heat treatments). If the solution after soaking for 1 hour is too concentrated (high pigment concentration), dilute all samples with distilled water (1 : 1) and repeat the measurement again. b. Cold treatment 1. The tuber pieces at the start of the experiment were put infreezer so it's frozen. 2. The frozen tubers are then washed quickly with tap water and put into a test tube containing 15 ml of water. As a control, place one piece of uncooled potato tuber in a test tube with 15 ml of water. 3. After incubation for 1 hour, measure the relative amount of pigment in the soaking solution with a spectrophotometer. If part A is diluted, then part B is also diluted. c. Treatment with chemical compounds 1. Place one cylindrical potato tuber each in 15 ml of methanol, acetone and tertiary butyl alcohol solution. 2. As a control, place one piece of potato tuber into 15 ml of distilled water 3. Incubate for 1 hour and measure the absorbance. Experiment b. Permeability of Living Tissue in Acid and Alkaline Solutions Objective: Seeing the effect of acid and base solutions on tissue membrane permeability Materials and Equipment: Plant material : leafRhoe discolor Chemical material : distilled water, HCl solution (0.025 N), KOH (0.025 N), acetic acid (0.025 N), NH4OH (0.025 N) Tools: 1000 ml beaker, drill to make shaped pieces cylinder with a diameter of 1 cm, spectrophotometer and cuvette, thermometer,freezer , test tubes, and razor blades. Ways of working : 1. Prepare an incision in the lower epidermis of Rhoe discolor and place it in distilled water. 2. Prepare the test solution (distilled water, HCl, KOH, acetic acid and NH4OH) into test tubes of 10 mL each and label them. 3. Place two epidermal tissue incisions in distilled water, two incisions in KOH and six incisions in NH4OH. Note the time it takes to turn blue after soaking. 4. After the color turns blue in the NH solution4OH, move the four incisions into distilled water. From distilled water, transfer two sections into acetic acid solution and two sections into HCl. Note the time for the color change that occurs in the tissue. 5. When the color change is complete, transfer the tissue incision into distilled water and return it to the NH solution4OH. Note the time it takes to change color again. 6. Perform procedures 4 and 5 three to five times and calculate the average time required for the color change from acidic conditions and alkaline conditions.