Authors: Eliza Ivanova(age 15) and George Velev(age 16)Edited by A. Chidester

• Some scientists say that the human body is “a walking periodic table”, since in contains a variety of chemicals found in our environment.

• Is this true? Let us find out!

Chemical compounds are generally divided into two categories.

In the first category are the inorganic compounds that are composed of relatively small molecules bonded ionically.

In the second category fall the organic compounds that mainly consist of carbon and hydrogen and build up the human body.

Certain salts (NaCl, CaCl), which are inorganic compounds, exist in the human body as dissolved in water.

More than 62% of our body is water. The percentage depends on the age of the human being- in children this percentage is higher than in an adult’s body. Our daily consumption of water is approximately 2.7 L. This amount of water may come from a variety of sources: food, metabolism, drinking, and etc.

H2O regulates homeostasis and the body is not able to function properly without it.

Any substance that releases hydrogen positive ions (when it is dissolved in water) is called an acid.

Any substance that releases hydroxyl negative ions is called a base.

An ionic substance that contains a negative ion other than OH- or O2- is called a salt.

When acid reacts with base, the products are salt and water. This process is called neutralization.

• The numerical scale that measures acidity or alkalinity is called a pH scale. It has values ranging between 0 to 14.

• The pH of water is 7. It is considered to be neutral. Any substance having a pH higher than 7 is considered to be acidic and any substance having a pH lower than 7 is considered to be basic.

• In order for homeostasis to be maintained in the human body, body fluids (including blood) need to have a relatively constant pH.

When a strong acid or base appears in the human organism, it may be destructive for the human cells. Substances called buffers (combinations of weak acids or weak bases and their respective salts in a solution) help the body fluids to resist changes in pH and to maintain the balance in the organism.

Carbohydrates are the major source of energy for most cells. They can be broken down in the cells in order energy to be released.

Composition: carbon, hydrogen, and oxygen in a ratio twice as much hydrogen as oxygen (example: CH2O, but they can be more complex).

1. Monosaccharides (comes from Greek) are the simplest type of carbohydrates. They are the building blocks of more complex sugars and cannot be broken down by hydrolysis.

2. Disaccharides (Di means 2) are the two monosaccharides bounded together. They all have the same chemical formula but differ in structure. (example: glucose, fructose).

3. The third type of carbohydrates are polysaccharides (poly means many). Polysaccharide chains (called polymers) may contain hundreds and thousands of monosaccharides. Their general formula is (C6H10O5)n, n-the number of glucose units in the molecule.

Fats are molecules that are rich in energy and are a source of food reserve and long-term fuel.

They are stored in the organism in the form of neutral fats or triglyceride.

Each fat molecule is composed of glycerol and fatty acids.

Two types of fatty acids exist:

- saturated fatty acids (solids at room temperature)

- unsaturated fatty acids – oils (liquid at room temperature)

These are fatty compounds containing alcohol, fatty acids, and a phosphate group (PO43-), often linked with a nitrogen containing group.

Fatty acidFatty acid

Fatty acidFatty acid

glycerolglycerol

phosphatephosphate alcoholalcohol

Every phospholipid has a hydrophilic head and non-polar tails. This is important, for phospholipids build cell membranes and they are all arranged with the water-loving heads on one side and the tails- on the other.

These are fat-soluble compounds composed of four bonded carbon rings, consisting of 17 carbons. Examples: cholesterol, male and female sex hormones, etc.)

Steroid hormones help regulate certain phases of metabolism in the body such as puberty, menopause, etc.

These organic compounds compose most of the tissues of the body.

They contain carbon, hydrogen, oxygen, nitrogen (sometimes sulfur), phosphorus, and iron.

Proteins form enzymes that control chemical activity (during the break-down of food molecules in the stomach), protect us against diseases in the form of antibodies, carry oxygen throughout the body, make up some of the hormones, express genetic information, and serve as indicators.

enzyme

A B

enzyme

AB

enzyme

A+B

Amino acids are the basic building units of proteins.

They always contain an amino group (NH2) at one end of the molecule and a carboxyl group at the other. An amino acid

contains one variable component. They may occur in different chemical combinations. They simplest amino acid

is the glycine. It has only one hydrogen atom.

We know only 22 amino acids in the living organisms. However, their large variety of combinations can

create more than 50000 proteins in the organism.

Nucleic acids are very large and complex molecules. They carry the body’s hereditary messages and regulate the synthesis of proteins.

The building blocks of NA are called nucleotides.

In 1869, the Swiss physician Friedrich Miescher first isolated them from the nuclei of human pus cells.

There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

•May be present in either the nucleus or the cytoplasm

•actually, there are three types - messenger R(mRNA) carries genetic information from DNA- transfer RNA (tRNA) is involved in amino-acid activation during protein synthesis- ribosomal RNA(rRNA) is involved in ribosome structure.

•Makes up the chromosomes within the cell’s nucleus

•holds the genetic code

•controls heredity

•Determines which proteins will be synthesized in a cell and thus controls the cell’s activity

RNARNADNADNA

• The energy that is produced from chemical reactions in body is stored in a small organic molecule called ATP(adenosine triphosphate).

• When energy is needed, ATP is broken down through hydrolysis and releases the necessary energy.

ATP ADP(adenosine triphosphate) + Pi(inorganic phosphate) + Energy

• Just before the end we would like to say that this is not all that can be said about body chemistry.

• No, we have just introduced you to the main processes, but there are a lot more.

• If you are interested in any other ones, why don’t you make a research for them by yourself!

• “Body Chemistry.” Human Anatomy and Physiology. 1990 ed.

• L’ organisme human. Le Petit Larousse en Couleurs. 1996 ed.

• “Introduction to Body Chemistry.” Chemistry in Brief. 1993 ed.

• Backgrounds created by Eliza Ivanova