Tiny machines

It’s been a while since I posted, so I thought it was about time I wrote something. And what better to write about, than what I spend every day working on!

If you studied biology in school may remember this: DNA RNA Protein.

Proteins do almost everything in the cell. Anything you can think of, a protein does it.

Generate energy? Protein.

Shuttle things around? Protein.

Repair damage? Protein.

At any one time, a cell has tens of millions of proteins, all working to keep the cell healthy and functioning as it should. It’s a mind-boggling operation, and it is happening in every one of your cells right now. When you consider that you have trillions of cells (there are more cells in your hand than there are people on earth!), the staggering complexity is difficult to grasp.

The cell needs to make all those proteins, and it needs instructions so it can make the right ones at the right time. These instructions are encoded in your DNA. Each “instructional” section of the DNA is called a gene, and every protein is encoded by a different gene. Every cell in your body has its own copy of the DNA (with some exceptions), and it is very precious. If the DNA gets damaged you lose the instructions for the proteins, and the cell will probably die as a result. Because of this it is stored in the nucleus, away from most of the things that could damage it. The problem is, proteins can not be made in the nucleus, so the cell needs a way to get the instructions for the proteins out of the nucleus, and into the body of the cell, the cytoplasm.

Life has come up with an ingenious solution to this problem: the cell can make a “photocopy” of the instructions of the protein it needs, and it can take that out of the nucleus. This “photocopy” is called mRNA, and it is then used to make as many copies of the protein that a cell needs. That way the DNA is kept safely locked away, but the cell can still make the protein. The process of “photocopying” the DNA to make mRNA is called “transcription”.

I like to think of the DNA as an enormous book, that is kept behind lock and key in a special room in a library. There is only one copy of the book, so it is kept safe, away from all the people that work and visit the library. The problem is, people need the information that is in the book. In fact the book describes how everything works in the library, so without that information, the library would completely fall apart.

To get around this, a small number of trusted people can photocopy pages from the book, and they can then be passed to the workers in the library so they can carry out the instructions. If the photocopy gets damaged it isn’t a problem; another photocopy can just be made.

In this analogy the photocopy is mRNA, and in reality, when it gets taken out into the cytoplasm, that is only the start of making a protein. The mRNA has to be transported to little machines called ribosomes, and the ribosome reads the mRNA, and produces the protein. This process is called “translation” because the cell is translating the instructions contained in the mRNA into a functional protein.

All of the tens of millions of protein in every cell are made like this, and the tiny machines (ribosomes) are at the centre of it all. They are amazing things; every single cell that has ever existed had ribosomes in it. Every animal, plant, fungus, and bacteria has ribosomes, all busily making protein from mRNA, sustaining all life in the process. And these ribosomes are what I spend my time studying.

Like everything in life, how they work is extremely simple and complex at the same time. The ribosome is shaped vaguely like a burger bun, with two parts, and it attaches mRNA with one part above and the other below. The mRNA then feeds through the ribosome until it has all been read. At the same time it is reading the mRNA, the ribosome is also making the protein (which is coming out the top of the ribosome in the gif above), so when it is finished reading, it is also finished making the protein.

For a long time it was thought that this process of reading an mRNA and producing a protein (translating the mRNA) was a pretty passive one. If the cell needed a lot of a protein, it would make lots of mRNA, and as a result, the ribosomes would make lots of protein. While that is true, we now know that it is not the only way a cell can make more protein, and that ribosomes have an important role in making sure that the correct amount of protein is being produced. If one ribosome is reading an mRNA, it will produce one protein. But if 10 ribosomes are reading the same mRNA, they they will produce 10 proteins. If a ribosome takes 20 seconds to read the mRNA, it will only produce half of the protein compared to one that takes 10 seconds. These (and many other subtleties) give ribosomes extraordinary control of the fate of the cell, and we are only beginning to understand this.

3d rendering of a ribosome

It’s not an exaggeration to say that understanding ribosomes is key to understand all life. They carry out one of the most key processes in life, but there is still so much we do not understand about them. We also know that many diseases hijack ribosomes, including cancer, so increasing our knowledge is obviously important, and that is what we focus on in my lab. Tiny, beautiful, complex machines, that are so important that life wouldn’t exist without them. And people wonder why I love my job so much!

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