Wednesday, 9 November 2011

tMoL: Big Cell, Little Cell

I’m writing this as a homage to one of my closest friends on the blogosphere. The every wonderful LabRat has finally ended her fraught relationship with scientific research and is throwing herself wholeheartedly into science writing. Whilst I am hugely envious, I wish her all the best and hope she will remember me when she is rich and famous. Look out for her in future publications.
By way of background; Lab Rat has always had a fixation with the simpler things in life, by which I mean bacteria.

False colour E. coli, bacterial/prokaryotic cells.
All living organisms are made up of cells individual living units which are relatively self-supporting and capable of total self-replication, although this is complicated by the intricate interactions between different cells in larger organisms. Whilst larger creatures, like humans are made up of billions of cells, the vast majority of life on Earth exists as single celled microorganisms that cannot be observed with the naked eye.
Cells fall into two main groups, larger and more complex organisms, plants, animals and fungi are called eukaryotes (that’s us humans too) and have much more intricate cellular structures. The earliest forms of life, with the simplest cells are called prokaryotes, which include bacteria.


Prokaryotic cells are small and relatively simple, 500 of these cells in a line would be just 1 mm long. The majority of important life functions of prokaryotes occur at the cell surface and there are few internal structures, compared with the many complex structures found within our, much larger cells.  This lack of internal structure means that each cell has a limited amount of space for processes such as energy generation so must always have easy access to food and air and have a limited maximum size. This limits the potential of prokaryotes to form structures, although there are a few exceptions, such as biofilms.

Eukaryotic cells (Green) with Prokaryotic cells (Red)
The genetic material of prokaryotes is mostly encoded on one circular piece of DNA, although there are a few smaller circles of DNA which carry a small number of extra genes. It is these small circles, called plasmids, these often carry genes which allow bacteria to become resistant to medication or allow them to grow under new conditions, such as extreme temperatures or high salt concentration. Plasmids can be transferred between bacteria, even between different species of bacteria, in a process called conjugation. This ‘horizontal’ transfer of genes means many cells can become rapidly resistant to drugs and is responsible for how quickly bacteria are able to adapt and change to new environments.

There are several similarities between all living cells. These core activities, including copying of genetic information and protein production are, on the surface, very similar. However, as my students should be able to tell you now, there are vast differences in the precise ways that they are carried out. The mechanisms in prokaryotes are much more straightforward and closely connected together than in humans and other eukaryotes. The prokaryotic approach to life processes is generally much more economical, every process contains many fewer elements and wastes much less in terms of time, energy and space. This also helps bacteria to live in much more challenging conditions than other lifeforms can survive. By contrast, they sacrifice precise control of their internal processes, which is important in other organisms to develop the specialised cell types needed for multicellular life.

Bacteria form the basis of life without sunlight on deep sea vents
The adaptability of prokaryotic life is really important in allowing bacteria to thrive in harsh environments that would kill other creatures instantly. They can survive the pressures of the deep ocean, the heat and toxic fumes of volcanic regions, they can be frozen in ice, handle excessive salt concentration and even lack of oxygen. These are called extremophile bacteria, lovers of extreme conditions. It is expected that if life survives anywhere else in the solar system it will be in the form of bacteria, and it may even have been in this form that life first arrived on this planet.

We often think of bacteria as the causes of illnesses, however this is a rare case. Bacteria are actually an essential part of our lives. For every one of your cells in your body there are at least 9 bacterial cells. These are particularly active and helpful in the digestive system where they help us to process food and loss of this natural prokaryotic population from your body would have very severe health consequences.

To find out more about the wonderful, invisible world of prokaryotes and the things that they do for us, follow the Lab Rat as her adventures continue. I also apologise to the Lab Rat for this relatively simple over view of her favourite organisms.

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