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.

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.

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.

Amino Acids Are Like the Letters of the Alphabet

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

When I’m talking about proteins, I tell the students that there are only 20 different amino acids. Yet from just those 20 “building blocks”, an infinite number of proteins can be formed. At first that idea is hard to grasp. Then I ask how many letters there are in the alphabet. They reply “26”. Then I ask how many words can be formed from those 26 letters. The light goes on. Then I comment on the fact that there are 26 letters but only 20 amino acids, but in forming words what makes the difference is the particular letters that are used, the number of those letters and the sequencing of those letters. All of the same variables are true in forming proteins from amino acids—PLUS the three-dimensional arrangement of the amino acids. It’s like playing 3-dimensional Scrabble.

Energy Conversion and iPods

Jennifer Wiatrowski, Pasco-Hernando Community College

Relating the function of mitochondria and energy conversion to the real world. I ask students if they could charge their iPods by plugging it into a lump of coal or a waterfall (they generally laugh and say “no”). I then ask them if there is energy in a lump of coal or a waterfall (they  say “yes”). So, I reason that in order to utilize the energy in the coal or the falling water, it must be converted to another form. For charging their iPod, it must be changed into electricity and this is accomplished by a power plant. Now, I ask them what is the main energy source for cells? (They usually know this is sugar from earlier in the semester). I then explain that sugar is like a lump of coal to a cell. Full of energy, but inaccessible in that form. So, the job of the mitochondria is to convert the energy in sugar into a form the cell can use, ATP.Roblox HackBigo Live Beans HackYUGIOH DUEL LINKS HACKPokemon Duel HackRoblox HackPixel Gun 3d HackGrowtopia HackClash Royale Hackmy cafe recipes stories hackMobile Legends HackMobile Strike Hack

Lock and Key Analogy with Enzymes

Written by Michelle Zurawski, Moraine Valley Community College

This is an analogy that is used during the enzyme discussion. I compare the enzyme substrate complex with a lock and key. My car is a cheap fuel efficient little car so I tell the students that I would like upgrade to a nicer Prius. I ask them if I could go to the parking lot and open a nice new Prius with my key. I then tell them that this is one of the ways that enzymes work to save energy. You only need a small amount of enzyme (1 key) to work with a specific substrate (1 car). Just think if you had to make a new key every time you opened up your car door. That saves energy by using that same enzyme (car key) over and over for the same reaction (car). Enzymes are specific to one substrate just like the key to my car is specific to my car. You can also use the two puzzle pieces fitting together like an enzyme and a substrate only fitting together in one way.

The Energy Barrier for a Chocolate-Craving Pregnant Woman

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

When discussing the energy of activation (EA) related to enzymes, I tell students about when I was pregnant and ate ice cream every night. I explain that after dinner I would sink into my deep, fluffy sofa. When I deemed it ice cream time, it was challenging to get up to get from the sofa with a big belly. I would complain and huff and puff,  etc. But sometimes, my lovely husband would hold his arm out and help to pull me off the sofa. In this analogy, my husband is the enzyme (catalyst) because he lowered the energy barrier for me. However, he didn’t make the impossible happen—I would have gotten that ice cream on my own—he just made it easier and faster for me to be a happy pregnant woman full of ice cream (the product of the reaction).

Using Food and Drink to Describe Osmosis

Written by Jennifer Wiatrowski, Pasco-Hernando Community College

I use two different analogies to relate osmosis to the real world:

a. I use two large beakers (beakers A and B), a jug of water and lemonade mix or fruit punch mix (these are dry powders). I then tell the class I am going to mix two classes of a refreshing beverage (nice in a hot climate like Florida). I tell them that I will make the first beverage very sweet, and pour in a large amount of lemonade or punch mix. The second beverage will not be nearly as sweet and I pour in a small amount of the powder. I then fill each of the beakers to equal volumes. I then ask the class if the two beakers have equivalent solutions. (They say no!). So, although the two beakers appear to have equal volumes, the amount of water is varies between the beakers. This shows students that the amount of water in a given space is influenced by the amount of solute. I then ask the students to imagine connecting the beakers together with a selectively permeable membrane and then ask them which way the water would flow  (from beaker A to B or B to A?)

b. I then talk about Martha Stewart. Martha always says that you should never toss your salad until your guests arrive or you are ready to serve it (I was recently informed by my students that “toss the salad” has taken on additional meaning……so this gets a good laugh out of the class). So, at the beginning of class, I take a bag of salad and some dressing and mix them. I then put it aside for awhile. In the meantime we talk about hypertonic and hypotonic. I then ask to think about the scenario with the salad and the dressing. They eventually reason that the salad is hypotonic to the dressing (or the dressing is hypertonic to the salad) and the consequence of this is a watery salad as the dressing pulls water out of the greens. This would make Martha HORRIFIED.  To finish, we take look at the salad we mixed earlier.