I. The chemistry of life

1.1 Read the text and pay attention to the highlighted words

Living organisms are made up of chemical substances. An element is a substance that cannot be broken down into simpler substances by normal chemical reactions. Four basic elements, carbon, hydrogen, oxygen and nitrogen make up 96% of an organism’s body.

Atoms are the simplest units of elements. Atoms are composed of protons, neutrons and electrons.

Different atoms are joined by chemical bonds to form compounds. Compounds are divided into two main types, inorganic and organic compounds.

Inorganic compounds

They do not have a carbon skeleton. Water and minerals are inorganic compounds. Water is the most important inorganic compound. The chemistry of life is the chemistry of water. Without water, life cannot exist. All life processes require water.

Minerals are needed for normal growth and development. Calcium and potassium are minerals needed for bone growth.

Major groups of biologically important organic compounds are carbohydrates, proteins, lipids, vitamins, enzymes, hormones, and nucleic acids.

Carbohydrates

They are the primary energy source for all organisms. Carbohydrates are divided into many types. Some are called sugars. The most important sugar is glucose, because it is very important for brain cells. Mostly we get carbohydrates from plants.

Lipids or fats

They are the secondary source of energy for organisms. They also have protective and supportive functions in organisms. Plant and animals contain fat.

In the human body, excess fat can cause some disorders, such as arteriosclerosis, which is the accumulation of fat molecules on the walls of blood vessels. Arteriosclerosis blocks the blood flow and may cause heart attack and even death.

Proteins

They have many vital roles in an organisms' body. They are part of many other organic molecules or structures. They are the structural compounds for all organisms, Hair and fingernails are made up of a protein called keratin. They are also used as an energy source. Antibodies, which kill microbes, are also made up of protein.

Vitamins

They are regulator molecules. They regulate normal growth and development. Vitamin A regulates normal eye function, vitamin D regulates normal growth of bone, and vitamin С is needed for immunity or body defense. They do not provide energy.

Enzymes

They are biological catalysts. Enzymes speed up biochemical reactions. Without enzymes life processes would be very slow. There are many enzymes in our body, such as pepsin, which acts in protein digestion in the stomach.

Hormones

They are chemical messengers in organisms. They carry messages from one organ to another organ, or to all of the body's organs. Hormones regulate normal body functions. Insulin is a hormone that carries a message from the pancreas to body cells in order to balance the glucose level in the blood.

Nucleic acids

They are not to be confused with the variouscorticosteroid drugs often prescribed by doctors for conditions such as rheumatoid arthritis. Anabolic steroids have only a very limited use in ordinary medicine.They are misused by some athletes and body builders in order to increase muscle size and strength. Because they are derived from the male hormone testosterone, they may also have the effect of stimulating aggression. Their use is prohibited.

They are master or director molecules. They control all life activities in the cell. DNA and RNA are the nucleic acids found in the cells. DNA functions like a director and RNA like a vice-principal.