Proteins are extremely large molecules made up of smaller amino acid chains. Most proteins can contain up to three hundred amino acids although there are some which are much smaller, and a few much larger. Because amino acids often contain carbon, proteins are considered organic compounds. There are twenty two basic amino acids which make up proteins and many of these are essential to the human diet in order for proteins to be made.
The sequence of amino acids found in various proteins depends solely on the gene which is coding for them. For proteins, twenty of the amino acids are used to make up the sequence. In a few instances, uncommon amino acids, such as selenocysteine and pyrrolysine do appear in protein molecules.
Proteins are considered the building blocks of life because they function in so many cell processes. Proteins known as enzymes, work as catalysts in many cells speeding up reactions that are important to cell metabolism. Although these proteins (catalysts) function in changing the speed of the reaction, they do not alter the actual reactants (known as substrates) in any other way. The enzymes function by lowering the activation energy allowing for the reaction to take place more quickly.
Proteins play an important role in the cytoskeleton of cells. Found in both eukaryotic and prokaryotic cells, the cytoskeleton helps to maintain the shape of the cell due to its many protein filaments. The cytoskeleton is also responsible for protecting the cell from what may be trying to enter it, helps with cellular motion by flagella or cilia and is important for what is transported within the cell itself.
Another important function of proteins is immunity. Antibodies which help fight off foreign invaders in the body known as antigens are made up of proteins. Antibodies, also known as immunoglobulins fight off bacteria and viruses that enter the body. There are five antibody types known and each one performs a specific role.
Signaling between cells is important and proteins play a role in this. Protein receptors are responsible for the communication between cells and within cells. These signaling proteins are coded for by specific genes and can function in the secretion of hormones and neurotransmitters, which affect most body systems.
Proteins also play a vital role in the cell cycle known as mitosis. Mitosis is cell division which occurs in eukaryotic cells and is a process where DNA is replicated and two identical daughter cells are formed from one original cell. Without proteins and mitosis, cells would not replicate and survive.
Source: Wiki and http://publications.nigms.nih.gov/structlife/chapter1.html
