The cell is truly a near perfect piece of natural engineering. I am still incredulous at the amazing tomfoolery it undertakes to keep life ambling down its path.
The cell is like a self-sustaining megacity; a metropolis with premium infrastructure. Everything is self-contained; it has a postal system, a government, and garbage disposal unit, all that makes a city great.
The functioning of a cell rests on five basic tenets: molecules, reactions, energy, governance and expansion. Every unicellular organism is required to fulfill all of these tasks; it is what they are built for.
Let’s look at these basic functions of a cell vis-à-vis a city and acquaint ourselves with this benign machine.
Every city needs construction material to build its buildings and infrastructure-the buildings and roads are what define a city. In that respect, we can consider molecules as analogous to this construction material. They are akin to the concrete and steel used in modern city construction; they help to build up the infrastructure of a cell.
Just like how a city is made up of construction material, everything in a cell is made up of molecules. Molecules make up the membranes of the cells, outer covering of organelles and they are the carriers of the genetic code (which we will see a little later). A cell is composed of mainly four types of molecules: carbohydrates, lipids, proteins and nucleic acid.
It’s not only the infrastructure that makes a city world class. One also requires people, businesses, transactions; one needs people to occupy the buildings and do work,i.e, business and economics. When the city engages in a viable business, it has a booming economy and that city comes alive.
It’s the same for a cell. For a cell, reactions are the people, the businesses, and transactions. We have all these molecules, but they need to do things, i.e., they need to react. Thus, reactions are the bedrock of the smooth functioning of a cell. They provide a means for the cell to undertake in business, and built its own viable economy.
Cells can create proteins, carbohydrates and anything else the cell is obligated to do from reactions. They serve the purpose of chemical creation and chemical transaction.
Now we’ve got a great city with infrastructure and businesses. But, what do we do when the people get hungry or when the machines-so vital for business-stop running? We provide them with energy.
In a city, we need energy to run business; in a cell we need energy to run reactions. This energy can be used to do work. The exact nature of this work can be multifarious: biosynthesis, heat production, movement of molecules. The energy can also come from various sources (depending on whether you are a plant, an animal or get your energy off of chemicals).
In this great hypothetical city of ours, we have constituted infrastructure, business and energy. All we need now is someone or something to govern and coordinate all these undertakings en masse. In the case of a city, it is the local government; analogous to that in a cell, is the genetic information or genome. The genes of a cell have coded information for cell functioning; when it should produce a certain molecule, when it should divide, which protein goes where and so on. So, the genes are vital to the functioning of the cell.
The information is physically manifested in the form of DNA (deoxyribonucleic acid) which is coiled up in the nucleus of the cell (which is akin to the seat of governance of the city). It contains all the genes; the information necessary for the functioning of the cell. The nucleus is like the forbidden city with impenetrably high walls. Nevertheless, there are small pores for entry; and if we were to enter the nucleus via one of these pores, the sight would be addling, to say the least. It would be an utter mess of coiled up DNA molecules, indeed the whole place would be rife with DNA molecules coiled up precariously around histone proteins.
Our city is all set to become great: it has good infrastructure, business, energy and governance. Now, if we want it to become a splendid spot on the world map, we have to make it big. The arms of the city have to expand from its tiny confines so that it can accommodate more people, more facilities and sustain large business.
The cell is the same. Only expansion in the cells case would mean reproduction. Here I use the word ‘expansion’ in the sense that by creating more copes of themselves, cells have an expanded reach and achieve more together. After all, many can do much more than just one. In the same way as the productivity of cities increase by expansion, so to do the productivity of cells increase when it ‘expands’.
Of course, the singular purpose of life is the perpetuation of DNA; of life. In this view, reproduction or ‘expansion’ is much more fundamental to cell than it is to our city. Indeed, a city doesn’t need to perpetuate itself!
So, the term ‘expansion’, could also refer to the expansion of life itself.
The above discussion is intended to give us a brief understanding of the cell.
But, I have a confession to make; things are not as rosy as I have portrayed them to be. It is true that the major functioning of all cells follow these five tenants. But, for cells that constitute a multicellular organism, additional tasks have to be undertaken.
They are equipped to undertake tasks that ostensibly do not benefit themselves in any manner; rather they benefit the whole organism. A muscle cell is a good example; it is built to twitch and contract on stimulation by electrical signal. Although, this purportedly does not help the functioning of a lone muscle cell; but, put many together and you’ve got a strong muscle, capable of lifting heavy weights (well, maybe not my muscles!).
But, anyway I hope this trifle piece of information has sparked your wonder about the remarkably amazing natural machine at the heart of all life: the cell.