Cell Membrane

⦁ Why does flip-flop occur rarely?
Because this change is so hard for phospholipids. For a lipid molecule do this, interaction between hydrophilic head of the lipid and hydrophobic tails of the other lipids has to be occurred. This interaction cant occur easily. Because of that, we can’t observe flip-flop often.1
⦁ Types of active transport .( Primary and secondary active transport)
Primary active transport is that transport occurs against concentration gradient by binding ATP to transporter for assuming.2, 3
Secondary active transport is that transport occurs by using biochemical concentration gradient with ion exchange and help of co-transporter.2,3
⦁ Membrane fluidity regulation
Membrane can protect fluidity by using various ways. Cholesterol is one of them. If the environment is hot for the cell, cholesterol can help firm packing to protect structure. It can hold lipids together by his interaction with head of phospholipids. Also saturated and uncaptured tails can change distance between molecules. This dense or weak structure protect cell. The membranes having more saturated lipids are effective against hot temperature; the membranes having more unsaturated lipids are effective against cold temperatures.4
Material and Methods:
⦁ Osmosis:
⦁ Firstly we prepared 3 dialysis tubes, 10 cm long, and then we closed with clamps. 5 ml of 2 M sucrose solution we prepared at first experiment was added to each tube with help of micropipette. After that, each one was tied firmly. We measured masses of all them and recorded lab notebook. We placed distilled water, 2 M sucrose and 4 M sucrose solutions into 3 distinct bakers. We put dialysis tubes with 2 M sucrose solution into the baker including distilled water, 2 M sucrose, and 4 M sucrose. We measured masses of dialysis tubes at every 15 min and then we recorded. After measurement, we dried dialysis tubes, and then put into the bakers again.
⦁ Osmosis in Plants:

At this part, we took 4 small pieces from an onion and we placed them onto 3 distinct slides. We closed with cover slide carefully for bubbles. Couple of drops from methylene blue for first, couple of drops from safranin for second, and couple of drops from water for third was added onto slides. We added nothing for last one. We waited 3 or 4 min, because stains need to dye cells. After that, we used microscope for observing them. We took from microscope and we opened cover slides to dropped salt, some drops of 10 M salt solutions. Then we closed cover slides and we placed them onto microscope again for comparing with first observations.
⦁ Effect of Temperature on Osmosis:

3 dialysis tubes, 10cm long, were prepared and we closed one side of them with clamps. 5ml sucrose solutions being 2 M were filled with couple of drops from blue, green, red dyes for each one. Then we tied them. Before we examined them, we weighed them. We filled ice-cold, room-temperature and 40o C water into 3 bakers. The blue dialysis tube into the baker with ice-cold water, the green dialysis tube into the baker with room-temperature and the red dialysis tube into the baker with 40o C water were put. After 40 min, we took second records of masses of dialysis tubes.

⦁ Cell Permeability:

We took pieces from beets fitting into a baker. 4 bakers were filled with water, boiling water, chloroform, EtOH (ethyl alcohol-C2H5OH). After a while, some changes occurred in the bakers as their colours. We determined and recorded changes.

Part 2
Minute In distilled water In 2M sucrose solution In 4M sucrose solution
0 12.1 g 11.9 g 12.2 g
15 13.7 g 12.2 g 12.4 g
30 14.7 g 12.3 g 12.2 g
45 15.6 g 11.8 g 12.2 g
Table 1.1- records of “osmosis” part of the experiment

Part 3:
Minute In ice-cold water In room-temperature water In 40o C water
0 12.11 g 9.63 g 4.04 g
40 14.67 g 12.23 g 15.27 g
⦁ In “osmosis” part of the experiment, we realized expected and different results. In distilled water, we saw the results we expected. (Table 1) We expected that water pass inside dialysis tube because the environment according to solution (2 M sucrose solution) is hypotonic (lower concentration) and this caused that water passed inside by passing semi permeable membrane. The mass of the dialysis tube which took water increased. At second part also was almost expected. We thought that the mass of the dialysis tube that was in 2 M sucrose solution won’t change because concentration of the solution baker and dialysis tube are same. This isotonic situation would cause a balance that doesn’t change masses between solutions. But also we observed some little changes. The reason of that could be this dynamic system. Even isotonic system still has movements between molecules inside it. We could see this change in measurements. The system against small changes was stable. At the last stage, it was so unexpected, outside dialysis tube was hypertonic (4 M sucrose solution). We were expecting that the mass of the dialysis tube decreases. The measurements or the table don’t show any change. The mass almost did no change. The experiment fail could be that dialysis tube wasn’t dried or the wrong solution was used in default of 4 M sucrose solution or it hadn’t enough surface area for molecular movements.

⦁ At the “Osmosis in Plants” part of the experiment, we wanted to observe osmosis under microscope by using onion cells with differences of conditions. We used 4 pieces and we added nothing, water, methylene blue and safranin to each one separately. Then we added NaCl solution onto samples and closed cover slides. We aimed to see differences (Because of hypertonic environment, cell membranes of onion shrike and occur a distance from plasma membrane and cell wall.). At first sample without water, we cannot see any changes because we couldn’t see organelles or components of cells (Figure 2.1 and Figure 2.2). We cannot determine cell membrane and cell wall. Also water didn’t change anything. We still couldn’t see effects of water or osmosis. However methylene blue made a difference for our observation, we could see that plasma membrane shirked and went away from cell wall (Figure 2.6 and Figure 2.7). Because of methylene blue achieved dyed cytosol and then when cell lost water, space between cell wall and plasma membrane is obvious. Safranin couldn’t make same effect. Like first and second one, safranin didn’t help to observations (Figure 2.8 and Figure 2.9). We couldn’t see parts of cell, so we couldn’t see differences before and after NaCl solution. We expected that safranin works, safranin couldn’t have worked because we couldn’t have closed cover slide well and bubbles could cause that safranin didn’t dye components of cell.

⦁ At part 3, we examined temperature for permeability. We used 3 dialysis tubes for 3 different conditions of temperature. We filled dialysis tubes with the solutions having same concentration (2 M sucrose solution) and then we observed colour changes in bakers and masses of dialysis tubes. If we talk about masses, we investigates Table 3.1. We saw the larger change in hot water than others. We can say why the change is bigger because of kinetic energy of molecules. In hot water, molecules have higher energy. This occurs of they move faster. This difference of speeds can get higher permeability. When ice-cold water and room temperature are observed, we couldn’t see a huge difference. When molecules are slower, permeability is lower also. If we talks about colour changes, we can say same stuffs. Red beaker shows that higher temperature affect permeability. When we observe the others, we could see smaller change. Sizes of beakers could affect change.

⦁ We wanted to see effect of kind of solvent for permeability. We placed pieces pf beet into boiling water, water, EtOH, chloroform and we wait for changes. Like on picture (Figure 4.1), boiling water have biggest change , then water, EtOH. However no change is for chloroform. Boling water happened deconstruction of membrane and increase energy of molecules. If we observe water, it can create hypotonic environment. EtOH made a different environment because alcohol destroyed lipid structures. At least, it could do this for surface cells and pigment of beet pass through baker. Chloroform couldn’t do observable change because chloroform destroyed even pigments. This caused why we can’t see any differences for chloroform.

[1] https://www.biochemistry.org/Portals/0/Education/Docs/BASC08_full.pdf. Page 10-11
[2] Reese, Jane B.; Urry, Lisa A.; Cain, Michael L.; Wasserman, Steven A.; Minorsky, Peter V.; Jackson, Robert B. (2014). Tenth Edition, Campbell’s Biology. United States: Pearson Education Inc. p. 135. ISBN 978-0-321-77565-8
[3] Cooper, Geoffrey (2009). The Cell: A Molecular Approach. Washington, DC: ASM PRESS. p. 65. ISBN 9780878933006.
[4] Jesse Gray; Shana Groeschler; Tony Le; Zara Gonzalez (2002). “Membrane Structure” . Davidson College. Retrieved 2007-01-11.

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