Cell Membrane bubble lab Honors Biology I

Interface between internal & external cell environment CELL MEMBRANES Interface between internal & external cell environment Controls what enters and exits the cell to maintain an internal balance called homeostasis Needed materials IN (i.e. glucose) Waste materials OUT (i.e. CO2) Provides protection and support for the cell

A Bubble is a lot like a cell membrane Phospholipids (a major cell membrane component) have a love-hate relationship with water. Head = attracted to water Tail = repelled by water SOAP MOLECULE has the same SPLIT PERSONALITY!

The hydrocarbon tail of soap mixes with & dissolves in other hydrocarbons (i.e. oils and fats). The head region grabs onto passing H2O molecules rinsing down the drain. Bubbles have 3 layers: middle = a thin film of water, inner & outer = soap molecule layers with hydrophilic heads facing water (toward the center) and hydrophobic tails pointing out

How Soap Works The hydrophobic tails of soap molecules embed in grease and oil, breaking it up into particles called micelles that lift off the surface and disperse into water. “Like dissolves like.” Non-polar, hydrophobic tails are LIPOPHILIC (“oil-loving”) & will embed in grease and oils that help dirt/stains adhere to surfaces. HYDROPHILIC heads remain in contact with water. Soap is an emulsifier, or it allows a compound that is usually insoluble in water to dissolve

MICELLES Aggregates of surfactant molecules, micelles have hydrophilic heads in contact with surrounding water (solvent), packing the hydrophobic tails in the center. https://en.wikipedia.org/wiki/Micelle

Materials • 1000ml beaker • 900ml water • 100ml dish soap • 25ml corn syrup • 4 bendable straws • 30 inches of string • 1 clean straw • Shallow tray • Straightened paperclip • Plastic knife

Procedures Create the bubble solution by mixing the water, soap, and corn syrup in the 1000ml beaker. Create a bubble frame by using the following instructions. Method One Bend 4 straws at elbows. Flatten the shorter ends of straws and fold flatted surface in the middle (See Fig. 2). Connect straws together by inserting short ends into long ends to create a square (See Fig. 3). Method Two Cut straws in 5 ½ inch lengths. Run a 30 inch string through all four straws. Tightly tie ends of string together to create a frame. Cut off loose ends of string.

Procedures 3. Create a ring of thread by tying a loop about two fingers wide. 4. Cut off the loose ends. 5. Place bubble frame into shallow tray 6. Add bubble solution to slightly cover bubble frame.

Important Notes: We will do this together and reveal procedures as we go that will need to be written down. Be sure to keep lab notebook away from the water. Be careful and respect your colleagues and their stuff. This lab has seven sections of procedures with data expected for each section. After describing observation, I will display cell concept. Describe the cell concept, as you understand it, in your own words. Describe how the soap bubble was used to model the cell concept.

Observation 1: Holding the straws of the membrane holder, immerse it into the pan of soap solution. Raise it out of the pan and allow the excess soap to drip off. Hold up the soap film-filled membrane holder and observe. Twist the two straw handles in opposite directions and bend the film into different configurations.

**Write down observations Things to consider…. Can you see the light shining of the surface of the soap film? Does the light pattern move when the membrane is still? What happens to the soap film as you move the straws?

Analysis and Results Fluidity You should be able to see movement in the light pattern, demonstrating that the molecules of the film are constantly in motion. The theory of the structure of the cell membrane is called the Fluid Mosaic Model. This means that the membrane is made of a pattern of many small molecules that are moving around and shifting position

Analysis and REsults Flexibility A lipid bilayer is a fluid arrangement within which the molecules can move freely through the plane of the bilayer. They can reorganize themselves into almost any shape without losing the contacts that satisfy their mutual attraction. The soap bilayer is actually less flexible than a cell membrane because a cell membrane is supported on both sides, one side by the cytoplasm and the other by lymph or other tissue fluids. So, whatever you are doing to the soap film, plus more, can be done to cell membranes without breaking them.

Observation 2: Place the tip of a clean straw into the bubble solution in the tray. Gently blow on the other end of the straw to create a bubble. Slowly lift the tip of the straw out of the liquid while continuing to fill the bubble with air. Allow the bubble to grow to a size of about 6” wide. Return the tip of the straw back into the bubble solution and try to create a smaller bubble inside the larger bubble.

**Write down observations Things to consider…. What does the smaller bubble inside the larger bubble represent? Are the functions of the multiple bubbles different?

Membrane Bound Organelles Analysis and Results Membrane Bound Organelles Eukaryotic cells feature membrane bound organelles that create specialized compartments within a single cell. The primary structure of the outer cell membrane as well as the membranes that enclose organelles is a double layer of phospholipids known as a phospholipid bilayer.

Observation 3: Make another film (MAF) in the membrane holder. Take the straightened paper clip. Stick the paperclip in the membrane and pass it through to the other side. MAF. Take the paperclip and dip it in the soap solution before passing it through the membrane. MAF. Stick your finger through. MAF Dip your finger into the soap solution, making sure that it is well covered, and stick it into the membrane. Move your finger around the membrane. Remove your finger from the membrane.

**Write down observations Things to consider…. Did the membrane seal around the paperclip or did it pop? What happens to the membrane when you remove your finger? Can the membrane heal around small punctures?

Self-Sealing/Self-Repairing Analysis and Results Self-Sealing/Self-Repairing Remember that the membrane is not a solid. It is made of two layers of many molecules attracted to each other. Like the bubble layer, cell membranes can spontaneously repair small tears in the lipid bilayer.

Observation 4: Dip loop of thread into bubble solution. MAF. Hold the frame parallel to the tray. Gently lay loop of thread onto film surface. Use dry object to break the bubble film that is inside the loop of thread. Insert paperclip through thread loop. Rock frame back and forth to observe thread loop. Gently move thread loop around with finger.

**Write down observations Things to consider…. Did shape of loop change once internal portion of bubble was popped? Were you able to move the paperclip through the bubble? Did the thread loop move when frame was shifted?

Analysis and Results Transport Proteins In a cell membrane, small molecules such as water can sometimes move into the cell through small spaces in the lipid bilayer. Larger polar molecules cannot pass through the membrane because of the non-polar tails in the interior of the membrane. The only way these molecules can pass in and out of the cell is through channels created by protein molecules in the membrane. The proteins form a polar tunnel through which the molecules can pass. Membrane proteins can also drift across the lipid bilayer.

Observation 5: Place the tip of a clean straw into the bubble solution in the tray. Gently blow on the other end of the straw to create a bubble. Lift the straw out of the liquid and continue to blow air into the bubble. Continue to gently blow air into the bubble as you slowly pull out the straw. As the tip of the straw leaves the bubble, you should be able to briefly observe a small tunnel existing between the bubble and straw tip.

**Write down observations Things to consider…. This tunnel is allowing air to freely move between the straw and the bubble without breaking the bubble film.

Analysis and Results Gap Junctions Gap junctions form between neighboring animal cells, allowing their cytoplasms to connect directly. This provides a quick way to move material between two cells including the rapid transit of ions and small molecules.

Observation 6: Take a straw and make a bubble about 8-10 cm across. Take a knife, wet it with soap solution, and starting in the solution at one side of the bubble, cut the bubble in half. Cut the two new bubbles in half. Keep dividing the bubbles until you have at least 10.

**Write down observations Things to consider…. What happens in the middle of the bubble when you cut it? Do the bubbles separate or stick together?

Analysis and Results Cell Division Cells divide when an organism is growing, when tissues need to be repaired, or when the surface area to volume ratio becomes too small (i.e. the cell grows too large). During cell division, a bilayer is created across the middle just like dividing the bubble. Also, your cells fit together in much the same manner as the bubbles with no space between. The type of cell division most like the bubble is binary fission. Some Single-celled bacteria reproduce by splitting into two. In binary fission, bacterial cells divide when a thin ring of proteins located at the cells midpoint contracts, effectively cleaving the cell in two.

Observation 7: Use a straw to create a few bubbles in your soap solution. Coax the bubbles toward each other and try to get them to fuse into a single big bubble. ***WRITE DOWN OBSERVATION

ANALYSIS AND RESULTS Cell Fusion There are circumstances in a cell where two membranes fuse into a single larger structure. Researches even fuse two cells together in a laboratory to create a larger cell with properties of each. (e.g. They can fuse an antibody-making cell with a cancer cell to get cells that keep multiplying and making antibodies.)

Questions? https://vimeo.com/52263821