Chemical Composition of Organisms

Basic Chemical Properties; an Introduction

All things are made from matter and although you may not always be able to see matter (as in the case of air), it is all around us. So what are in these substances of matter that are all around us? – Atoms.

Atoms are exceptionally small units made up of three basic subatomic particles; protons, electrons, and neutrons.

Each atom becomes different from the next by having different number combinations of these subatomic particles. The different numbers of protons, electrons and neutrons determine different elements or in other words a pure substance made from a solitary kind of atom.

Every element has different qualities or physical characteristics for example oxygen and gold. The former is a gas that is one of many elements making up organic matter. Where as the latter is solid and inert (a non-reactionary element).

Simple Chemical Reactions

When two or more elements come in contact with one another, a reaction takes place which results in a chemical bond or link between the atoms and it forms a substance, a chemical compound.

We discovered briefly in the introduction that inert (or noble gasses) means non-reactionary. These elements; helium, neon, argon, krypton, xenon, and radon have a special electron configuration which makes them very stable. Their valence shell or exterior shell is complete and full. Other elements try to achieve this stability by reacting with each other and sharing electrons from their outer most shells.

All of these chemical reactions also experience a change in energy. Some release energy (exothermic) and some absorb it (endothermic). Some of them are called spontaneous reactions and occur as soon as the two elements come in contact with one another. Others require activation energy to begin the chemical reaction process.

There are 2 different types of chemical bonding; ionic and covalent. With the former, electrons are transferred completely from one atom to the other in order to complete the valence shells of each atom. The two atoms are then held together by electrostatic forces. These ionic bonds are always formed between metals and nonmetals. They dissolve easily in water and then can conduct electricity efficiently.

With covalent bonding the atoms don’t give up their electrons freely but share them and this is because both atoms have a related tendency to gain electrons. This usually happens between two nonmetals. When the electrons are shared the ionic charge doesn’t exist and therefore the molecules can move freely as a liquid or gas when kept at room temperature.

Properties of Water

Water is made up of one oxygen and two hydrogen atoms (H2O). The hydrogen atoms are bonded covalently to the oxygen by a shared pair of electrons. There are also two unshared pairs of electrons remaining on the outer shell of the oxygen molecule.

Water has 3 states. The solid state occurs below freezing (as ice or snowflakes). Between freezing and boiling temperatures water is a liquid and above boiling, water becomes a gas.

Water contracts until it reaches four degrees Celsius and then it expands until it becomes solid. This is contrary to most liquids which generally contract with a temperature decrease. Because of this, solid water is less dense than liquid water and that is why ice floats. This unique quality is due to the hydrogen bonds. Holding the molecules further apart as a solid is a result of having 1 less hydrogen bond per molecule. Hydrogen bonding also allows water to display nearly universal solvent properties.

Water molecules are attracted to other water molecules. This is due to the fact that the oxygen side of water has a negative charge and the hydrogen side has a positive charge and it is called cohesion. When water is attracted to other materials in this way it is called adhesion.

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Chemical Structures of Carbohydrates, Lipids, Proteins, and Nucleic Acids


Carbohydrates are the first category of organic compounds or organic chemistry. Carbohydrates are essentially made up of three elements; carbon, hydrogen, and oxygen and they generally taste sweet to people.

When a carbohydrate is comprised of one molecule it is called a monosaccharide. If it is made from two that are connected then it is referred to as a disaccharide. When there are three or more molecules we call them polysaccharides.

Glucose, which is represented as C6H12O6, is basically an energy used in all living things. It dissolves in blood and or water. Because of this, it can be carried to all cells in the body. After it is metabolized in cells, it delivers energy. Glucose is also present in plant matter and is the dominant product of photosynthesis.

Next, we will discuss lipids which are also known as fats.


Lipids are made up of carbon, hydrogen and oxygen as well. However, lipids contain less oxygen than carbohydrates. The three main kinds of lipids are as follows; simple lipids (fats and oils), compound lipids (glycolipids and phospholipids), and derived lipids (steroid).

Lipids cannot be emulsified in water however can dissolve in organic solvents such as ether or chloroform. They can also be broken down into fatty acids and glycerol which can eventually break down more to produce more energy.


The chemical compounds required for the process of life are known as proteins. They are massive, complex molecules each made up of thousands of atoms. Again containing the three main elements; carbon, hydrogen, and oxygen. They also contain nitrogen but can also include sulfur and phosphorus. All living things are composed of proteins.

Nucleic Acids

There are two types of nucleic acids; DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid). These are the basis of cellular reproduction and division.

A cells DNA contains the genetic blueprint in a catalogued form and is only existent in the nucleus of the cells made from DNA. RNA is present in the nucleus of the cell and the cytoplasm.

The two differ from each other in that DNA has deoxyribose and RNA has ribose. As well, the types of nitrogen bases in each are slightly different.

The Origin of Life

The conundrum of “the chicken and the egg” is paramount when considering life itself. How did life begin? Science dictates that our universe evolved and each structure became increasingly complex through a series of anomalies. Galaxies, starts and atoms were assembled out of particles created The Big Bang. First the heavier elements were developed from stars. After these stars started to age they pushed out the heaviest elements. Finally, biological evolution began from microscopic bacteria-like cells. These became the basis of all life on earth. Simpler structures bore more complex ones and this cycle continued until today. Organic molecules were the building blocks for the origin of life and are thought to have existed in an elemental soup created by the BIG BANG.

It is assumed now that the current DNA/protein system we know and understand today was not possible as one cannot exist without the other. (Back to the chicken and egg dilemma) However, scientists believe RNA acted as a precursor to both. In a way, it can function as both catalyst (like a protein) and as a genetic code carrier.

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