Sometimes I just like to be silly.
Let me qualify that.
There are times, particularly when immersed in the complexities of metabolic pathways, that it really pays to do something different, to lighten the mood and provide another way of looking at something. Of course, you also want to provide something that helps the students understand a tricky concept, and if what you do is unusual and memorable, then it will also help them retain that understanding.
Here are my dramatis personae:
Yes, you got that right. A purple cuddly elephant (a Xmas present from a tutor pupil), 2 juggling balls, an apple, a top hat and 3 dissection pins. Let’s see if the Biologists among you can figure out what I’m trying to illustrate. My students did!
So, first, I arranged the props as follows…
The elephant, lying on its back, with both juggling balls and one dissection pin, safely tucked between its legs. To one side and a little ahead, the apple with 2 dissection pins jabbed into it; on the other, also a little ahead, the top hat, brim up.
What am I trying to show?
At this point, of course, they haven’t a clue. But they’re already giggling. If nothing else, I have avoided that cardinal sin of teaching, being DULL.
I then slide the elephant along the table, making little dooby doo noises. More giggling. But I’ve got their attention! They really want to know what this is about.
When the elephant arrives between the apple and the hat, it becomes agitated! I switch from dooby doo noises to zips and zaps…
…things start to change! I take the dissection pin off the elephant and plunge it, with a pleasing “thunk”, into the apple. And I take one of the juggling balls off the elephant and put it in the hat. Note that the apple now has THREE dissection pins in it, which is the clue that enables them to guess the first clue…
Ah! Is that ATP???
Indeed it is. The molecule that acts as energy currency in cells, adenosine TRI-phosphate, with each dissection pin being a phosphate group. The apple with just two pins was ADP, adenosine DI-phosphate. By making a molecule of ATP, by transferring a phosphate from the elephant to the apple, we’ve manufactured some useful energy for the cell to use.
And making ATP this way is called…?
Substrate level phosphorylation…
Testing them without testing them, they get all the benefits of retrieval and application and usage, without the stress of doing something that scores them out of 10…
But what do the other things represent?
Let’s start with the elephant. It’s clearly (ahem) a…?
exactly, with how many carbons?
yes, the 3 carbon fragment that you get from splitting?
right, after the glucose has been?
well done, at the start of?
And the molecule we end up with? The elephant deprived of its dissection pin and juggling ball is?
So that’s the context and the pathway. They know all this, they’ve just not seen it represented with cuddly animals and edible fruit.
But now to the key bit…
What’s the juggling ball and what’s the top hat?
Again, they’re on top of this, now that the context is clear. The juggling ball represents hydrogen, stripped from the sugar phosphate by dehydrogenase enzymes, and the top hat represents NAD, the hydrogen carrier that is reduced when it receives the hydrogen from the sugar phosphate via the enzymes.
It’s worth stressing the importance of this. In order to convert sugar phosphate into pyruvate and make essential ATP, you also have to have an empty top hat.
But how do we empty the top hat so that we can keep doing this, and keep making ATP?
No problems here – they are all confident that the top hat delivers the juggling ball to the electron transfer chain in the mitochondrion, enabling it to come back and accept another juggling ball from the next elephant to pass by.
Trouble is, this only works in the presence of oxygen. What happens if there’s no oxygen? What happens if the top hat cannot pass on the juggling ball in this way?
Short answer, the whole thing stops. No more elephant conversion, no more triple pinned apples, no more energy for cell, in a word, death.
How else could we empty the hat? What else might be prepared to accept the juggling ball from the hat, freeing it up to go and help convert another elephant?
This takes them a little longer, but with a few nudges and winks and helpful joggling of the relevant prop, they get it…
Notice what we have here. We still have the triple pinned apple (the essential ATP), but we also have an empty hat because the juggling ball has been returned to the elephant.
(nb: what I really need here is another elephant to demonstrate that the process can continue…. note to self – buy more purple elephants)
But we don’t have pyruvate anymore. A purple elephant with one juggling ball (pyruvate) that accepts a juggling ball (hydrogen) from a top hat (NAD) has become a different molecule – a purple elephant with two juggling balls – or as biochemists like to call it, lactic acid.
The mystery of anaerobic respiration revealed, emphasizing the importance of oxidising NADH.
They liked this. They also liked this….
Hope you do too.