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Cells are the basic functioning units of an organism. Unicellular organisms exist as only one cell while multicellular organisms contain multiple cells, sometimes even trillions. Cells have two main characteristics. They exchange energy with their environment to survive, and they contain genetic instructions in the form of DNA for how to function. This allows each cell to produce and replace its own components, as well as to replicate itself entirely.

Eukaryotes vs. Prokaryotes

Living organisms can be divided into two major groups based on the characteristics of their cells: prokaryotes and eukaryotes. Prokaryotes are unicellular organisms such as bacteria, whilst eukaryotes encompass a wide range of organisms, some of which are unicellular e.g. yeast, and others which are multicellular e.g. plants and animals.

Prokaryotes are biologically simpler and more geologically ancient than eukaryotes. In spite of their simplicity, prokaryotes are the most successful group of organism and are much more common and diverse. Prokaryotic cells are so prevalent on earth that even within our own bodies there may be many more prokaryotic bacterial cells than eukaryotic human cells, possibly 10 times as many comprising up to 1000 different species!

There are several key differences between prokaryotic and eukaryotic cell but the key defining difference is that eukaryotic cells contain membrane-bound organelles whilst prokaryotic cells do not. Organelles are structures within the cell which perform specialised functionsAs the name suggests, they are like mini organs, with specific functions. For example, mitochondria generate energy for the cell. In prokaryotes, whilst discernible structures do exist within the cell, none are enclosed within a membrane bilayer.

Some differences between eukaryotic and prokaryotic cells © 2014 Wikipedia

Because they are relatively simple, synthetic biology is often focused on engineering prokaryotes or unicellular eukaryotes. Many synthetic biology case studies will involve bacteria such as E. coli or yeast like S. cerevisiae or S. pombe due to their genetic tractability. Whilst genetically engineering plants and animals is possible, there are more practical and ethical limitations involved.

Cell types 

In multicellular eukaryotes, cells can differ hugely in their morphology and roles, working together to produce a complete functional organism. For example, nerve cells are specialised to carry electrical signals very rapidly throughout the body whilst cells that line the intestine are adapted to absorb nutrients during digestion. These different cell types will have different patterns of gene expression and hence very different proteomes, specific to their function.

In humans there are over 200 different cell types, all containing exactly the same DNA but performing a huge range of functions. This demonstrates the importance of regulating which genes are expressed and to what extent, rather than simply the genomic DNA present within the cell.

Stem cells

Stem cells have unusual and useful properties for both healthcare research and synthetic biology. They exist in an undifferentiated state, meaning they are capable of producing other cell types. Most tissues within the human body contain a small reservoir of stem cells which can replenish the cells of the tissue as they are lost. For example, the stem cells responsible for replacing the cells in our blood produce between 1011 and 1012 blood cells each day.

At the extreme end of cell potency, pluripotent stem cells are capable of producing any cell type in the body. Historically these stem cells have been obtained from the very early stages of an embryo, although scientists are developing new and better techniques to convert adult cells into pluripotent stem cells. Pluripotent stem cells are a very important area of research for healthcare. It is hoped that stem cells can be used to regenerate specific tissues, for example in the treatment of neurological injuries such as paralysis.

Embryonic stem cells are pluripotent © 2016 GabSoucisse

View full profile James Severin from Paddington, London


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About the authors

View full profile Jérôme Lutz from Berlin & Munich, Germany

I like to share the great things I discover daily while researching and working in the field of Synthetic Biology.

When I talk to people about it, they often refer to Science Fiction. However, when I send them links to this wiki and they read through those pages, they start understanding that this is real and it's happening right now.

View full profile Jake Curtis from London

I am a student at Cambridge University who has just finished a BA in Natural Sciences, focusing on Genetics in my third year. I am now studying for an MSc in Systems Biology.