Complete HSC Biology Notes Band 6 Section 1: Most organisms are active in a limited temperature range Identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity in substrates Role of enzymes in metabolism (control rate of metabolism) - metabolism refers to all the chemical reactions occurring in organisms - chemical reactions are needed for growth, repair and to make substances need for other cells. - enzymes are biological catalysts which increases the rate of chemical reactions - without enzymes, metabolism would be too slow to support life - enzymes speed up reactions by lowering their energy, and also used in small quantities – allows them to be used over and over again Chemical composition of enzymes - enzymes are made of proteins of the elements: carbon, hydrogen, oxygen and nitrogen - proteins consist of long chains of amino acids held together by peptide bonds - when enzymes denature, these bonds are broken, protein loses shape and cell becomes inactive Enzyme specificity on substrates - the chemical on which enzymes act upon is called a substrate - extremely specific in their actions; each enzyme acts on ONE substrate only (controls one type of reaction) - lock and key model: o the shape of the enzyme and the active site on the enzyme have a specific shape which fits onto the substrate forming and enzyme-substrate complex. The reaction occurs and the enzyme breaks away from the products. - modified to the induced fit model. An analysis of shapes of molecules shows that the active site is more flexible than a ‘key hole’ and can slightly alter its shape to fit more closely with the substrate.