Peanut Butter Sandwich: Cell Membrane Structure

Written by Kathy Watkins, Central Piedmont Community College

The phospholipid bilayer is like two slices of bread with peanut butter.

The peanut butter is like the hydrophobic center (fatty acid chains). The phosphorous containing heads are like the two pieces of bread.

(Students might be asked to explore how the sandwich can be modified to represent channels, proteins, and cholesterol, etc. in the membrane.)

 

Using Analogies in Microbiology: The Bacterial Cell as an Entertainment Venue to Illustrate the ATP-binding Cassette (ABC) Transport System

Written by Kristen Z. Swider, Capital Community College

Students in my microbiology class are relatively unfamiliar with the scientific concepts involved in the course and will often attempt to rely on memorization. However, due to the complex nature of the material, it is difficult to access information from the perspective of pure recall. As abstract concepts are discussed throughout a science course, many learners still operating in the concrete stage of development may be lost by a failure to attach understanding to anything of substance. As a result, the concepts are often missed during examinations. There is no requirement that an instructor complicate the approach in order to communicate scientific principles. For these reasons, the use of analogies to illustrate complex processes can enhance a student’s comprehension of the material and make connections that promote lifelong learning. Analogies may be presented to the learner as prepared elements of a lecture or they may be generated by the learners themselves. Self-generated analogies can and do occur spontaneously in discussion. Students are encouraged to develop and present analogies to the class. In either case, the interactive, social process of exploring analogies, whatever their source, contributes to the learning process.

How the ATP-binding Cassette (ABC) Transport System Works

- ATP-binding cassette (ABC) system: This involves substrate-specific binding proteins located in the bacterial periplasm, the gel-like substance between the bacterial cell wall and cytoplasmic membrane.

- The periplasmic-binding protein attaches temporarily to the substance to be transported and carries it to

- Meanwhile, ATP gets broken down into ADP, and phosphate, releasing energy. It is this energy that powers the transport of the substrate, by way of the membrane-binding transporter, across the membrane and into the cytoplasm.

- Examples of active transport by means of ABC systems include the transport of certain sugars and amino acids. There are hundreds of different ABC transport systems in bacteria.

ANALOGY:

The Bacterial Cell as an Entertainment Venue to Illustrate the ATP-Binding Cassette (ABC) Transport System

The players:

Bacterial cell: Entertainment Venue

Substrate: Patron

Periplasm: Outer arena area

Substrate-specific binding protein: Event ticket

Cytoplasmic membrane: Inner arena barrier with turnstiles

Membrane-spanning transport protein: Turnstile

Cytoplasm: Event location (inner arena)

ATP: energy needed to move the turn-stile and allow entry of the substrate (Patron)

- The bacterial cell is the entertainment venue, with the cell wall being the outer boundary of the arena property. Once the patron reaches the arena, he/she can easily migrate through the cell wall to the inner arena (periplasm) since a “ticket” is not yet needed.

- In order for the patron to gain entry into the main arena area of the venue (cytoplasm), he/she must pick up a ticket at a will call/box office. Here in the periplasm, a patron will pick up a pre-prepared ticket (periplasmic binding protein) just before the entering the event.

- Before entering the main arena area, the patron with the ticket (transportable substance and periplasmic binding protein complex) must enter the arena through the turnstile (membrane-spanning transport protein). A turnstile is a form of gate which allows one person to pass at a time. A turnstile can restrict passage only to patrons who provide a coin or a ticket. It can also be made so as to enforce one-way traffic of people.

- Once at the turnstile, the ticket (periplasmic binding protein) gets left behind, and the transportable substrate (patron) can enter the cell via a turnstile.

- As the substrate (patron) moves through the turnstile, energy is required, and ATP is broken down. The patron (substrate) is now in the arena and can be used by the cell.

 

Universal Currency in the Cell

Written by SuEarl McReynolds, Palo Alto College, San Antonio, TX

ATP is sometimes referred to as the “universal currency” of energy. I explain that it’s like there was only one kind of money in the world. Since Americans are pretty self-centered, we would think it should be dollars. So there would be no pesos or francs or Euros or yens, etc—just dollars. And there would only be dollar bills—no $5’s, no $20’s, no nickels, no dimes, no quarters—just $1 bills. If you wanted to buy a piece of gum, it would cost $1 bill. If you wanted to buy a new truck (this is Texas, you know!), you’d have to show up at the dealership with a bunch of wheelbarrows of $1 bills.

Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell

Written by Jennifer A. Metzler, Ball State University

When discussing thermodynamics and why cells do not break the laws because they are so organized, even though entropy is always increasing, I ask them to think of the place where they live, whether a dorm room, apartment, or house. Then I ask them to think of the difference between keeping it clean and organized or letting it become messy and disorganized. I ask them how much energy it takes for them to keep things clean and organized versus messy and disorganized. They all answer more energy to maintain order. So, then I discuss how cells are no different, if they want to maintain order they must constantly take in energy, and when they stop doing so they die and lose their order. Also, mentioning that they maintain the ever increasing entropy by giving off heat.

Satellite TV and Photosystems

Written by Jennifer A. Metzler, Ball State University

When discussing how a photosystem works to capture light energy, I ask students to compare it to a satellite TV dish. The job of the dish is to capture and focus the TV signal so they can watch their favorite show. The job of the antenna complexes is to capture the light energy and then pass that energy (focusing) to the reaction center so that light energy can be passed on in the form of excited electrons to begin converting the light energy into chemical energy in the first stage of photosynthesis.

Using Waves at the Beach to Describe Concentration Gradients

Written by Jennifer A. Metzler, Ball State University

When discussing passive versus active transport and the difference between an input of cellular energy, I ask students to imagine they are at the beach or at a wave pool. Since passive transport is going down a concentration gradient, I tell them to liken it to having the waves at their back and moving into shore. It is not a problem for them at all and they do not need to expend any energy as they are going with the flow. With active transport going against the concentration gradient, I tell them to imagine turning around and having the waves hit their chest and try to move away from shore. In this case they must expend energy as they are going against the flow of the waves.

Phone Batteries and Cellular Energy

Written by Michael Sawey, Texas Christian University

Your cells need the energy from ATP in order to do their work… just like your phone needs the energy from its battery. But that battery needs to be recharged. ATP is like a fully charged battery. As a cell does its work, such as a muscle contracting, ATP’s energy is “drained.” Just like your phone’s battery can be charged and drained over and over, ATP can be used over and over. When ATP is “used up” it is changed into a slightly different molecule called ADP. ADP is like a dead battery. To “charge” the ADP up to ATP, the mitochondria in your cells need oxygen and glucose. During Cellular Respiration, a chemical process uses the reaction between oxygen and glucose to charge ADP to ATP. When it does this, the oxygen and glucose are broken apart and recombined into carbon dioxide and water. These are “waste products” and are flushed out of your body by the Respiratory and Urinary systems (with help from the Lymphatic system). This is why you must breathe and eat constantly. Every time you do so, you are taking in new supplies of oxygen and glucose that can be used to “charge up” ATP from ADP. Just like you do not throw away your phone battery when it is dead, you do not lose ATP when its energy is used up. It is simply converted to ADP, waiting to be charged up again.

Dance Club Patrons Describe Water Molecules

Written by Dave Sheldon, St. Clair County Community College

I approach the changing density of H2O by having students imagine a high energy dance club. They imagine the loudest and most energetic night club that they can, and describe it in detail. They focus on the intense energy, the motion of the people and the number of people on the dance floor. I include some techno music to get them thinking! Once focused on the high energy and rapid motion of the patrons, I modify the scenario. First I drastically reduce the energy by cutting the music, killing the strobes and bringing up the house lights. My students describe a ringing of ears and a much slower movement by the club patrons. Second, I describe every person as an H2O molecule with their arms outstretched in front of them at a 90° angle. Their hands represent two Hydrogen atoms and the middle of their back represents their Oxygen atom. Hydrogen bonding causes them to place their hands on the backs of two other people while two more people place one of each of their hands on your back. With low energy in the club, these bonds last for a relatively long time and the water molecules form a low density crystalline lattice. The people on the dance floor during the high energy rave would no longer fit in this low energy orientation. Some even note that they may actually be forced out of the club through windows and doors, which is what happens when water freezes.

Customize Your Auto Like Proteins Are Customized in the Cell

Written by Dave Sheldon, St. Clair County Community College

When discussing the function of the Golgi apparatus, I ask my students to picture a friend, two identical automobiles and an automotive customization shop. I ask them if they and their friend purchased 2 identical cars (same color, make model etc.), would it be possible to customize or detail them in a way that would result in two totally different appearing and performing cars? The answer always comes back “yes” and we discuss ways to modify an automobile. Ground effects, spoilers, window tinting, sound systems, paint jobs and fancy rims are usually mentioned. The car in this analogy represents a newly formed protein that has just been sent via a transport vesicle from the rough endoplasmic reticulum (auto dealership) to the Golgi apparatus (detailing shop). They imaginary car pulls into the receiving or Cis side of the shop and leaves via the shipping or Trans side of the shop. While in the Golgi detailing shop, the modifications represent chemical reactions such as phosphorylation, glycosolation and manipulation of the size of the polypeptide chain.

Aerobic Respiration Gives a Cell More “Spending Power”

Written by Jennifer Wiatrowski, Pasco-Hernando Community College

Relating the value of aerobic respiration to the real world. The students in introductory biology have very little interest in cellular respiration. But, I want them to understand that there is greater value (in terms of ATP yield) between aerobic and anaerobic respiration (like with exercise). So, I relate the processes to “dollars in your pocket” and “spending power at a fancy restaurant.” Anaerobic processes give your 2 ATP or 2 dollars in your pocket. Could this buy you anything at a fancy restaurant? No! This is not a lot of spending power. If you complete aerobic respiration, you have approximately 38 ATP or dollars in your pocket. Could this buy you something at a fancy restaurant? Yes! Now, you have spending power.