tMoL: The Meanings of Life - Boxes, little boxes

I’m creating this section as a means for me to blog without having to put in too much effort. In each post I’m going to pick one of the many words and acronyms developed by academics to confuse everyone else, and explain it for everyone to understand, and provide you with a few useful little facts. The first few are going to be pretty easy, words that come up in the media all the time. Words that everyone has heard and probably knows the meaning of but not necessarily some of the more interesting bits.

Cell – I want to start with cells because they are an important part of my work, they are generally most active and undergo the most changes during development. They are also the basis for life and are generally the start point of most discussions of the evolution of life (although actually there was a lot of good stuff before that, which tends to get overlooked). Also I will be talking about them to local school children in a few months and hopefully this will help me to organise some of my ideas.

A cell is the basic unit of life, the smallest thing that can still count as alive. Most of the species living on Earth spend their entire lives as a single cell (bacteria, algae, amoebae), very few exist beyond this; consisting of billions of cells (Plants, Animals, Fungi). Most people now are introduced to cells at school, before they have the chance to drop sciences and run off to healthier subjects of study. I certainly remember drawing “animal cells” as a big black blob with a wiggly line all around the outside. Is it really that simple, is every animal on Earth just a big pile of wiggly blobs with dots inside? Makes us all sound a bit like frogspawn doesn’t it? Well, simply put, no, otherwise all the cell biologists could have retired years ago.

Cells are often confused with atoms (the basic unit of everything). Cells are billions of times larger than atoms, cells are simply the smallest thing that can be considered alive i.e. that do all of the things that make you count as alive. Being alive, however, is actually very hard to do and so requires a very complex structure to achieve, hence why cells are much, much larger than atoms.

The wiggly line with a blob way of showing a cell is actually a historical matter. Cells were first seen using very weak microscopes. The first cells were actually seen in a sample of cork. Many dyes used in these early experiments were drawn to DNA and hence it showed up as a dark blob inside the cell. The wiggly line, the cell membrane, is a layer of fats which surrounds the cell, similar to the way oil floats on a puddle. In this early work, cells were seen as little rooms within a plant or animal, it is this comparison that led to the name “cell” referencing regularly arranged small square rooms, as in prisons and monasteries. We now know that cells are considerably more complicated than small empty rooms; they have many different compartments inside them, which do different things and communicate with each other, it is like a smaller version of your body. You have specific organs to process information, gain energy, dispose of waste, obtain oxygen, to move and to reproduce. Similarly a cell has different organelles dedicated to related functions; I will discuss these in future posts.

Most cells actually have very specific shapes and different groups of cells look and act very differently, very few are wiggly blobs, as such there is no such thing as an “animal cells” there are in fact several hundred different types of cell in your body all with specific jobs. Red blood cells have a doughnut-like shape which helps them carry oxygen. Nerve cells are extremely long and thin allowing them to carry messages over long distances. Cells in your gut have extensions called microvilli which help you absorb food. A select few, such as white blood cells, are very wiggly, this allows them to move easily around between the other cells of your body, protecting you against infections.

Probably the most famous group of cells are stem cells. These are not just one cell type but many, the type that most people hear about are embryonic stem cells (ESCs), but there are many other more specialised types, some of which are present even in adults. Many cells in our body cannot make more of themselves, and cannot replace themselves if damaged. These cells are terminally differentiated; they are so specialised for their function that they are prevented from doing anything else. A good example is a red blood cell, its function is to carry oxygen, in humans red blood cells lose the nucleus (which has all the information for making new cells) so that they can use the space to store more oxygen. Stem cells solve the problem of how terminally differentiated cells are replaced. A stem cell is a type of cell that can make more of itself and that can make new cells of different cell types. ESCs are particularly exciting as they can make any cell type in your entire body but they are only found in developing embryos. However there are others which produce only certain cell types. Haematopoeitic stem cells are found in bone marrow and make blood cells. Stem cells in your gut help to replace the lining of your stomach and intestines when they are damaged, whilst stem cells in your skin constantly renew the outer layers and maintain hair follicles. These stem cells are more limited in terms of potential but are more easily available as they exist throughout adult life and so may be useful in future medical applications.

In future posts I’ll be looking at some of the elements that make up cells and that are usually significant in new scientific discoveries.