Protein Functions Essay PDF

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2007/2008 Q1. Write an essay entitled “The Functions of Proteins’. Proteins are the key functional molecules in life. The importance of proteins is underscored by their name, which comes from the Greek word proteios meaning “first place”. Proteins are instrumental in almost everything organisms do. They have many structures and therefore many functions. Some proteins speed up chemical reactions, while others play a role in structural support, storage, transport, cellular communication, movement and defense against foreign substances. Consistent with their diverse functions, they vary extensively in structure, each type of protein having a unique three-dimensional shape. 1. Enzymatic Proteins: The function of this type of proteins is to accelerate chemical reactions. Life would not be possible without enzymes. Enzymatic proteins regulate metabolism by acting as catalysts, chemical agents that sped up chemical reactions without being consumed by the reaction. For example, digestive enzymes catalyse the hydrolysis of the polymers in food (e.g. lipase). 2. Structural Proteins: These long-chain proteins play a role in structural support. Crosslinking and intertwining allows for many properties. These proteins can be flexible and elastic (wool fibres), or strong and rigid (collagen fibres). For example, insects and spiders use silk fibres to make their cocoons and webs, respectively. Collagen and elastin provide a fibrous framework in animal connective tissues. Keratin is the protein of hair, horns, feathers and other skin appendages. 3. Storage Proteins: The function of storage proteins is to store amino acids. Metabolism of these proteins provides building blocks to make new proteins. For example, ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo. Casein, the protein of milk, is the major source of amino acids for baby mammals. Plants have storage proteins in their seeds. 4. Transport Proteins: This type of protein transport other substances. For example, hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from the lungs to the other parts of the body. Other proteins transport molecules across cell membranes. Aquaporins transport water across membranes, glucose transporters shuttle glucose into cells where it is needed rapidly for cellular energy. 5. Hormonal Proteins: These proteins coordinate an organism’s activities. For example, insulin, a hormone secreted by the pancreas, helps regulate the concentration of sugar in the blood of vertebrates. Sugar levels

need to be kept at a constant level in the blood to provide fuel for energy and for the functioning of the carbon skeleton. 6. Receptor Proteins: The function of receptor proteins is to allow cells respond to chemical stimuli. Ligands are the stimuli receptor proteins detect (e.g. hormone proteins). Signal transduction is the result of receptor binding its ligand. Receptors built into the membrane of a nerve cell detect chemical signals released by other nerve cells, such as serotonin or dopamine (neurotransmitters). 7. Contractile and Motor Proteins: These proteins allow movement. For example, actin and myosin are responsible for the contraction of muscles. Other proteins are responsible for undulations of the organelles called cilia and flagella. 8. Defensive Proteins: Defensive proteins protect against disease. For example, antibodies combat bacteria and viruses by recognising antigens through their shape. This type of protein is particularly variable....