Basic Biology -  Molecules of life - Proteins

Proteins the building blocks of life

Proteins are the main building blocks and functional molecules of the cell, taking up almost 20% of a eukaryotic cell’s weight, the largest contribution after water (70%). Proteins are made from small molecules called amino acids. There are many types of proteins some of which are:

• Structural proteins
  which can be thought of as the organism's basic building blocks. An example is collagen, which is the major structural protein of connective tissue and bone.
  
  
• Enzymes
  which perform (catalyse) a multitude of biochemical reactions, such as altering, joining together or chopping up other molecules. Together these reactions and the pathways they make up is called metabolism. For example the first step in the glycolysis pathway, which is the conversion of glucose to glucose 6-phosphate, is catalysed by the enzyme hexokinase. Usually enzymes are very specific and catalyse only a single type of reaction, however the same enzyme can play a role in more than one pathway.
  
  
• Transmembrane proteins
  are key in the maintenance of the cellular environment, regulating cell volume, extraction and concentration of small molceules from the extracellular environment and generation of ionic gradients essential for muscle and nerve cell function. An example is the sodium/potassium pump.