This is the first fun week in my biology class. (Fun for me) We’re starting to talk about energy and how it is handled and used by living organisms. As usual, my class is focused on animal cells as my standard model, but this all applies to any cell really.
The big topics of the week are to understand the nature of energy through the lens of the first (and second) law of thermodynamics. It’s the one that says, ‘Energy cannot be created or destroyed, only converted from one form to another’. The second law adds on a statement about entropy and how all energy conversions are less than perfect. The result is loss of energy – typically in the form of heat.
So, energy can’t be created or destroyed, fine. What does it matter to us?
It matters because (to paraphrase the author of our textbook, Mader): Life itself is but a temporary condition purchased at the cost of a continuous expenditure of energy.
“Well, in our country,” said Alice, still panting a little, “you’d generally get to somewhere else — if you run very fast for a long time, as we’ve been doing.”
“A slow sort of country!” said the Queen. “Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!”
We haven’t talked about where the energy comes from (specifically) but we do know that plants and other autotrophs convert solar energy into chemical energy that can be stored as sugar. However, when that energy is required to get something done it must be converted into a more useful form: ATP.
ATP is the coin of the cellular realm. Prokaryotes and Eukaryotes alike use ATP to power their enzymes. Enzymes are molecules that do cellular work, whether it be moving substances across a membrane, building complex molecules, replicate DNA or any of the many other functions of the cell. Enzymes do the work, ATP supplies the power.
Enzymes take reactants and combine them or break them to form products. This reaction happens where the reactants bind in the active site of enzymes.
We will also be looking at how enzymes are regulated within (or outside of) the cell. It wouldn’t do to have enzymes active all the time. What if a digestive enzyme became active as soon as it was made? It could damage the cell that made it. What is DNA polymerase was active all the time (we haven’t discussed this enzyme in class yet, but it copies DNA)? Random extra copies of DNA would not be useful.
Instead, enzyme activity is governed by two major types or regulators:
1. Competitive Regulators
2. Non-Competitive Regulators (There are also non-competitive activators as well)
No one enzyme does it all alone though. Instead, there are many, many enzymes that each have very specific jobs to do. These operate in conceptual pathways made up of strings of enzymes each doing one part of the work along the way. These pathways are referred to as metabolic pathways and may build (anabolic) or break down (catabolic) other molecules.
A last for of enzyme regulation involves the end product of a series of reactions going back and acting as an inhibitor to an early stage of the process. This is known as feedback inhibition and can be a very valuable way to save energy.
I hope that acts as enough of a primer for class this week because I’m getting tired and starting to find myself staring at the screen here in front of me for long moments. Here’s a trippy clip from the 1985 TV adaptation of Through the Looking Glass with Carol Channing and Ann Jillian: