The above image depicts the chemical structure of the molecule ATP.
Let’s talk about the cell again! More specifically, the energy transportation of the cell and a little molecule called ATP (Adenosine Triphosphate). As we discussed earlier, chemical reactions are very important to a cell; indeed, it is one of its basic functions. A menagerie of reactions go on in all of our cells every second; a bond is made, another one broken, some atoms exchange partners, and many other wondrous events that form the quiddity of a chemical reaction. And if you can recall from last time, we found that energy is vital for a reaction to occur. Besides, a multitude of other activities require energy as well: muscle contraction, movement of molecules, reproduction, etc. So, you can imagine that the cell is a prodigious power hungry machine. Depending on the organism, there are an assorted number of ways to obtain energy; some do it with the help of sunlight, some harness the energy of chemicals trapped in our Earth, and some still feed on other organism. But regardless of the source, the energy is still used in the same way.
All the more complex cell obey a principle of compartmentalization, i.e., where tasks of the cell are carried out in specific discrete compartments—known as organelles. Things are not spread out all over the place; rather there are different specialized areas of a cell that undertake different specialized tasks. For e.g., production of proteins are done in ribosomes (an organelle), destroying de trop materials are done in lysosomes (another organelle), etc. This allows for these processes to be localized, and it generally makes the cell a lot more efficient; if the chemicals for the many processes needed for a cell are spread all around the cell, they would indubitably clash and hence, not much would be able to happen.
Before going any further, I would like to expatiate on this discussion a bit more with an analogy. Let’s make a comparative between the cell and city again (click here to read more on that). In a city, there is compartmentalization, and specific activities are done in specific areas; manufacturing has its own area, governance has its own building, companies have their own offices, there are separate areas for living, etc. The area that would be interesting for us is the power generation area; it is the area where the electricity, an imperative for the city, is produced. Now, this power—although produced only in the power station—is needed in all areas of the city. How do we provide the other areas with this power? In a city, we would use a power grid; it can transport electricity to all parts of the city.
In cells too, we have specific area or organelles for energy production, e.g., the chloroplasts in leaves, or a mitochondrion. But as noted above, this creates another exigency; the energy produced in these organelles need to be transported to other areas of the cell for proper functioning. We need a method to provide all the areas of the cell with energy. This is where molecule ATP comes in.
Adenosine Triphosphate, or ATP, is the energy currency of the cell. It acts like a battery, containing stored energy that can be used later. It is like the power grid of the city; energy is produced in one part of the cell is stored and transported to all other parts of the cell through ATP. Due to the chemical nature of this molecule, it has immense energy storing capacity. The energy storing capacity of ATP, rest on a basic fact of chemical bonding. To form a chemical bond, we must give energy; to break one, we will get energy. The stronger the bond, the more goes into making it. So, one can store energy in a chemical bond, and break it to obtain that same energy as needed.
ATP consists of a base molecule adenine, and is connected to three phosphate groups. The bond between adenine and phosphate is immensely strong; on breaking it, a prodigious amount of energy is released. This is essentially what happens in a cell. A mitochondrion or a chloroplast produces energy, and packs it into an ATP molecule; this can then be broken by hydrolysis (reaction with water), rereleasing the energy created earlier. ATP is used all throughout the cell; every action, every reaction of the cell requires ATP. It can be seen moving all around the cell.
In this way, the cell adroitly circumnavigates a pertinent problem with a deft solution; a simple application of the simple laws of chemistry to produce benign biology. Therefore, it is no secret that ATP is extremely important to life. Without it, you would literally be starving for energy.