why water

It has been raining lately and this made me think of water. In my Nov 7, 2008 post (water world), I mentioned that water is the most abundant component of cells. In that post, I corrected a common misconception, that water is a universal solvent. It is not! It's just a very good solvent but it definitely is not a universal solvent!

In today's post, I will try to answer why water is the most abundant component of cells. Well, the reasons are because of its physical and chemical properties.

What are these properties? Among its important physical properties are: high specific heat, high heat of vaporization, high heat of fusion, high surface tension. Its dipole moment as well as its ability to form hydrogen bonds are its important chemical properties.

So what is so important about these physical and chemical properties? Well, because of its physical properties, water remains as liquid in a large range of temperature. It takes a lot of energy before water can be converted to vapor (high heat of vaporization) or solid (high heat of fusion). It can also absorb a lot of heat before its temperature changes even one degree centigrade (high specific heat). Thus, water does not easily get heated nor cold and this stability is very important for cells. If water is easily converted to vapor or to ice, can you imagine what would happen to our cells and to us if we find ourselves in very high during summer or very low temperatures during winter?

The high surface tension of water is also very important. This causes water molecules to create a film on surfaces and this is very important especially in maintaining breathing surfaces of our lungs.

The chemical properties of water are of course the reasons why water is a very good solvent. Their chemical properties allow them to  participate in many biological processes that keep us alive.

So there you are, those are the reasons why water is the most abundant component of cells.

Major biomolecules of cells

Every cell needs 4 major molecules, little bits of odds and ends, and plenty of water. These major biomolecules are: carbohydrates, lipids, proteins and nucleic acids.

Carbohydrates are used mainly as energy source for cells. However, some carbohydrates are also used as structural components. Cell walls for example consist of carbohydrates. Some components of the cell membrane as well as the extracellular matrix are also carbohydrates.

Lipids on the other hand make up the basic component of the cell membrane. They are also the major backbone of steroid hormones as well as the main form of stored energy.

Proteins meanwhile have both structural as well as functional roles in the cell. Structurally, they are major components of the cell membrane. Functionally, they act as enzymes, hormones, carrier molecules, antibodies, and several other roles.

Nucleic acids are of course the carriers of hereditary information of cells.

cell design 101

“If you were to design a cell, what would be your basic requirements or design?” This is the very first question I always ask my students about cells. Their answers always include: “nucleus, cytoplasm, cell membrane, organelles, etc.” When they answer this way, I then ask – “Is the bacterium a cell?” Of course they will answer “yes.” This answer is then perfect for my next question: “But the bacterium does not have a nucleus, so why did you list it as a basic requirement for your cell design?” I always follow this up with more questions and answers that eventually make students think really hard of what are the basic requirements of cells. This then sets the stage for my first lesson on “cell design 101” – wherein we will eventually agree that the basic requirements for cell design are simply: cell membrane, genetic material and biosynthetic machinery.

You can click on any of the links above and they will bring you to related post about these basic requirements for cell design.