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The Chemicals of Living Cells ©The Wellcome Trust 2 The chemicals of life All living organisms are made up of chemical substances Reactions between these substances keep the organism alive. They are living processes. The sum of all the chemical reactions in an organism is called it metabolism Enzymes 10 Enzymes are special proteins They are present in the cytoplasm of all cells They help to speed up the chemical reactions in the cell There are hundreds of different enzymes but each enzyme speeds up only one kind of reaction For example, glucose and fructose might join up slowly to form sucrose glucose- -fructose With the right enzyme present, the reaction happens faster glucose- -fructose 12 The molecules fit the shape of the enzyme enzyme substrate A substrate B 13 14 substrates combine temporarily with enzyme enzyme joins substrates together 15 enzyme unchanged and ready for next reaction new compound released by enzyme Different types of enzyme reaction 16 The last 4 slides show how an enzyme is involved in combining substrates to create a larger molecule For example, the enzyme could be building up a sucrose molecule from glucose and fructose An enzyme can also help to break a large molecule into smaller molecules For example an enzyme can split a sucrose molecule into the smaller glucose and fructose molecules A ‘breaking-down’ reaction the shape of the substrate molecule fits the enzyme shape this is called the active site of the enzyme 17 18 Intermediate stage (1) substrate combines temporarily with enzyme enzyme will break molecule here 19 Intermediate stage (2) substrate splits and separates from enzyme 20 Final break-down products enzyme ready for next reaction end-products Properties of enzymes 21 Enzymes can act on only one type of molecule They always produce the same end products Although they take part in the reaction, they are not used up Because enzymes are proteins, they are denatured by heat or some chemicals Denaturing involves a change of shape in the enzyme molecule so that it cannot combine with the substrate Individual enzymes work best at a particular temperature and pH (acidity or alkalinity) Enzymes can act on only one type of substrate this substrate cannot combine with this enzyme this substrate cannot combine with this enzyme 22 Because enzymes are proteins, they are denatured by heat or some chemicals enzyme denatured by heat enzyme + substrate denatured enzyme cannot combine with substrate 23 pH = % hydrogen ions • The pH of a substance is the measure of its acidity. • pH is measured on a scale from 1 to 14. pH of substances o To measure pH an indicator is used. Indicators change colour depending on the pH of the substance they are mixed with pH in food production Yeast and bacteria grow and reproduce within specific ranges of pH In cheese-making sometimes bacteria are used to help change the milk into a more solid form (coagulation). The bacteria produce lactic acid The bacteria can tolerate slightly acidic conditions In bread-making yeast produce carbon dioxide (CO2) during the process of fermentation. CO2 dissolves into water to form carbonic acid. Yeast cells prefer neutral environments to grow and reproduce