Proteins are very complex substances found in all living organisms; they are involved in the chemical processes that are necessary for life and also have important nutritional value About 20% of the human body is made up of muscle protein. Human blood serum, milk and eggs contain proteins. Plant proteins occur mostly in the seeds of legumes and cereals (Koshland, 2014). Proteins serve numerous functions in biological processes; their functions are related to their structure (Berg, Tymoczko & Stryer, 2002; Brooker et al., 2010). Protein molecules are large and are made up of amino acid chains. About 20 amino acids occur naturally while others are synthesized. The protein’s amino acid sequence along with their chemical properties and physical properties causes proteins to fold into three-dimensional shapes (Berg, Tymoczko & Stryer, 2002). Plants are able to synthesize all amino acids while animals cannot do so; however, all amino acids are essential. Proteins differ from specie to specie as well as from organ to organ (Brooker et al., 2010; Koshland, 2014).
Proteins interact with one another as well as with other biological molecules to form compounds that are important for life processes – such as transmitting signals in a cell and DNA replication (Berg, Tymoczko & Stryer, 2002). Proteins also contain numerous functional groups such as alcohols, carboxylic acids, thiols, carboxamides, and thioethers. When these functional groups combine in diverse sequences, they enable the protein to perform various functions. For instance, enzymes are proteins that catalyze chemical reactions in living organisms; their actions depend on the chemical reactivity of the functional groups in the protein (Berg, Tymoczko & Stryer, 2002). Enzymes catalyze reactions in biological processes such as DNA replication, metabolism, and digestion (Koshland, 2014).
Structural proteins are not as active as those involved in processes like cell signaling, but they are also very important. They can rigid or else somewhat flexible. The rigid units act as a form of internal skeleton in cells and tissues. The ones with some flexibility can act as springs and hinges that enable proteins bind with one another or with other molecules to form complex. Such flexible proteins are also involved in the transmission of information within the organism (Berg, Tymoczko & Stryer, 2002; Koshland, 2014). Structural proteins are found in such tissues as muscles, cartilage, nails, collagen, feathers and hooves. Collagen is a structural protein of ligaments, bones, tendons, and skin. Keratin is a structural protein that occurs in the epithelial cells of skin as well as nails, hair, feathers and hoofs (Koshland, 2014).
Proteins occur in all living organisms. Protein molecules are made up of amino acid chains of which about 20 occur naturally while others are synthesized. All amino acids are essential to life. Plants can synthesize all amino acids, but animals do not have that ability. Proteins play numerous roles in biological processes based on their structure. Proteins function as enzymes, transport and storage agents for molecules like iron and oxygen, support molecules, and the transmission of nerve impulses. Proteins are essential to the chemical processes upon which life depends.
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- Berg, M., Tymoczko, L. & Stryer, L. (2002). Biochemistry 5th Edition. New York: W H Freeman. Chapter 3 Protein Structure and Function. Retrieved 28 August 2014 from http://www.ncbi.nlm.nih.gov/
- Brooker, Widmaier, Graham, and Stiling. (2010). Principles of Biology. Koshland, D. (2014). Proteins. Encyclopedia Britannica. Retrieved 28 August 2014 from http://www.britannica.com