Welcome to Cell

shitty diagram
shitty diagram

You might remember a diagram like this from a biology course you took a  number of years ago and have since forgotten. While it’s fun to label the components of a cell, this exercise doesn’t really give you a feeling for what a cell is about.

In metaphor, you should think of the cell as an underwater metropolis contained in a protective barrier. Within the metropolis are specialized districts, each with its specific function working to sustain the metropolis as a whole. Within the cell there is the microscale equivalent of nuclear power plant, a network of highways, a towering array of skyscrapers, an incomprehensibly productive manufacturing sector. There is a highly refined waste removal system and a grand repository of information containing the city’s blueprint which also instructs the city’s destiny. It’s a dynamic place with a million different components whizzing and whirling about. It’s a far cry from the static image you might’ve experienced in an intro biology course.

 

grandiose, complex
grandiose, complex

How did the Cell Come to Be?

 

The exact details will never be known, but inquiry has lead us to some pretty interesting theories as to the creation of the cell.

just like lego
An example of a complex organic molecule. The black spheres are carbon atoms, linking in an interesting arrangement with other atoms

Let’s rewind time a few billion years. The oceans covered the Earth and its atmosphere was a scorching milieu of various compounds. This atmospheric milieu was populated by a handful of simple, inorganic compounds. The unique properties on Earth allowed these simple, inorganic compounds to react and create more complex organic molecules. This is the early Earth equivalent of taking chicken shit and making chicken salad. The hallmark feature of organic molecules is their placement of the carbon atom at the centre of action. In the world of elements, Carbon happens to be that badass piece of Lego that can attach all the other pieces to it to make more and more complex pieces. The forementioned atmospheric inorganic molecules are boring as shit by themselves, but when they react together to form complex, carbon-centred organic molecules, interesting things can happen.

miller-urey
just add heat, a little electricity.. and voila!

And that they did. If you take a handful of inorganic molecules, add just the right amount of heat and a bit of electricity, you end up creating all the basic molecules of life.  What are these molecules of life? Well, in a general sense, they are a collection of organic molecules that you will find common to every living thing. More specifically, they are the sorts of things you might find on the back of a nutritional label: fat, protein, carbohydrates. In fact, there are four broad classes of molecules that serve as the basic building blocks of life: fats, carbohydrates, amino acids (which make up proteins) and nucleic acids. So. Instead of adding magic, just add enough heat and electricity to the atmosphere in the Early earth and you create complex molecules from the simple molecules that were floating around.

The  building blocks of life and the building blocks of cells are simple to make. But how do you construct a city without cranes and a construction crew? And who gives the orders?

the cell membrane is essentially a thin layer of oil
the cell membrane is essentially a thin layer of oil

This is where things get crazy. Again, when imagining the cell, imagine a metropolis in water sealed by a barrier. The actual barrier found in the cell is essentially a thin film of oil (or fat. Same thing, but oil sounds better). Think of what happens when a drop of oil hits water – it sticks to itself and doesn’t want to bother with the water. This is the same sort of process that created the spherical barrier on the cell we call the cell membrane. Now, the actual cell membrane gets a little more complicated, but on a basic level we can see how its essential structure is created (that is, by adding fat + water and getting a sphere of oil). The formation of the membrane is a key component of the cell. The membrane separates the inside of the cell (and all that happens there) from the outside of the cell (and all that happens there). This is an obvious but important point.

Now, imagine that as each of these spheres of fat form, they capture a population of those complex organic molecules referenced before: a little nucleic acid, some carbohydrates, some amino acids. Cool, now you have a microenvironment with some organic molecules floating in water. That by itself isn’t too special, but say we were to add a layer of complexity to things.

It was just with heat and electricity that from simple inorganic molecules we got more complex organic molecules. Next up, the cell creates more complexity for us: here’s how.

Imagine a scenario where contained in one of those membranes there is a population of the organic molecules we’ve talked about exhaustively… and then something else. This something else is a quirky property of one of the types of molecules that happen to be entrapped within the membrane. As luck would have it, a group of nucleic acids trapped in this membrane have the added property of containing information. What the fuxk does that mean? Well it means that instead of floating around aimlessly, with nucleic acids going here, amino acids going there and carbohydrates doing whatever, this special group of nucleic acids now mean something to the other molecules floating around.

How does this go down? Well, this is a monogamous sort of affair. The information containing set of nucleic acid now forms an everlasting relationship with the amino acids that are floating around. Instead of bouncing into each other like strangers, the specific parts of the nucleic acid embrace and hold on to specific amino acids every time they come in contact.

 

put two amino acids together, call it a peptide bond
put two amino acids together, call it a peptide bond

This bringing together of amino acids is the fundamental process of construction in living things.

DNA is the nucleic acid in question. It contains the information that instructs the synthesis of proteins from amino acids.

It is simple and it is magical. These amino acids are versatile parts, and at the instruction of DNA, the amino acids can be assembled into a variety of things: pumps, propellers, highways and skyscrapers.

This assembly process is like if I put a gigantic version of the word ‘HOUSE’ in an ocean with construction material in it and allowed the word to float, and as it floated and bumped into the construction material, the material would stick to the word, self-assembling into a  bungalow

Let’s recap where we’ve gone:

  • from the atmosphere of the early Earth, add heat and electricity to make complex carbon based molecules called organic molecules

  • create a membrane separating an inner water filled compartment from the exterior

  • as a matter of chance, have a group of these organic molecules contain information that adds order to some of the other molecules. This ordering process uses the raw material floating around within the membrane (the amino acids) and in doing so constructs a registry of little molecular devices that can be used as parts to build even more complex things.

At every point, notice that something has happened to increase complexity and order. First it was the creation of complex molecules from the early Earth atmosphere. Next it was the creation of a unique and separate microenvironment with the cell membrane, in the process trapping and separating a collection of the complex molecules from the world outside of the membrane. Next it was the appearance of this remarkable information containing molecule–DNA–in one of the cells which provided more order and complexity around it by creating complex structures from the molecules floating around with it in the membrane enclosed compartment.

It is from this sort of process –  of adding complexity and order to things – that the cell was built. And soon from the individual cell we had communities of cells forming organsims – the sort of organisms that became more and more complex and went on to swim, fly and run across the earth.

So much for a static image with some boring labels.

@eeo361

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