Life: “It’s all in the DNA'”

Before I get started I want to start with the reasons why DNA is so important.

I mentioned that we’re all made of cells in a previous post. These cells are regularly dividing to form new cells, either to let us grow (as a child) or to replace old and used up cells.

A similar process happens during reproduction. We put two half cells together to make a brand new cell, which is an unborn child (this will then grow into a full blown adult).

One of the questions that hounded scientists for eons was: How do the cells know what we are? (As in, how does it know that we are human, and not a dog, or a cow or any other animal. What makes it a human cell – Surprisingly for some, if you look at each individual cell there are not many differences between animals.)

Are we really that different?

Perhaps just as important was the question: How does the cell know what it is? (as in whether it is muscle, fat, skin or brain. There is actually a huge difference between these types.)

So here was the first answer: Proteins.

I have mentioned how proteins are what allow us to do what we want to do and make us who we are. This is because proteins are functional and do things. Therefore if a cell has proteins that are specific to muscles, that cell must be a muscle cell.

Likewise if a cell has proteins that are specific to humans, then that cell is a human cell.

N.B. Some proteins are not specific and can be found in all animals, and all cells. (although there are usually some slight variations that don’t make much of a difference).

OK so proteins define the cell, and define the person. Now there is a new problem:

What defines which proteins are made? 

That is where DNA comes in. I’m not going to explain how it works just yet, that will be one of my next posts. but I will say this:

Almost everything about us, how we are made, how we connect each part of our body together, how each organ is allowed to function, is defined by the DNA.

DNA tells us which proteins, and where. Without DNA, we wouldn’t exist.

Because of this it is often referred to as, quite accurately, the ‘code of life‘. If you could read what the DNA said, you would have all the information you needed to make life. Again that is for the next post.

Now for some perspective:

Every cell has the same amount of DNA. That makes it sound like DNA is quite small. But if you took one cells worth of DNA and stretched it to it’s full length, it would measure around 2 metres. That’s pretty stretchy considering that one cell is smaller than this dot. A lot smaller.

Want more emphasis? The most pessimistic estimate for the number of cells in the body I could find was 10 trillion. So if you took the DNA of every single cell in the body and laid it end to end, it could stretch from one end of the solar system to the other.

6 times.

Earth is the 3rd planet from the sun. At this distance you could barely make out that there is land in there.

The most optimistic estimate for the number of cells in the body was over 100 trillion.

Think about it, we have at least 6 solar system’s worth of information for life stored inside all of us.

It’s all in the DNA, and the next few posts are going to explain how. Possibly with the normal aside note 🙂

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  1. Life: DNA – Breaking The Code | Science Defined
  2. Life: In the Making… Fertilisation | Science Defined
  3. Embryology = Evolution = DNA??? | Science Defined

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