Proteins are present almost everywhere in the body. 50% of the dry weight of the organism is protein. Proteins are the building blocks of all living organisms. All enzymes are proteins but not all proteins are enzymes. Enzymes, hormones, antibiotics etc. that regulate biological reactions are special types of proteins. All plants and animals contain protein. Proteins exist in viruses, bacteria, blue-green algae, algae, fungi, lichens, etc.