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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 cytoplasm (and the organism) alive. They are living processes. The chemical substances described in the next series of slides are carbohydrates, proteins and lipids, but there are hundreds of others. Carbohydrates Carbohydrates contain the elements carbon, hydrogen and oxygen Familiar carbohydrates are sugar and starch Glucose, fructose, maltose and sucrose are sugars Glucose and fructose have the same formula, C6H12O6 Sucrose and maltose have the same formula, C12H22O11 Carbohydrates provide the main source of energy for respiration in living organisms 3 4 Glucose C6H12O6 C HO C HO C H C HO C H C C C H C OH H C OH C H2OH A glucose molecule as a straight chain O C 5 of the carbon atoms may be arranged in a ring This molecule is often represented simply as a hexagon Other carbohydrates 2 molecules of glucose can join together to form a molecule of maltose sucrose is formed when a molecule of glucose and a molecule of fructose combine maltose Starch and cellulose are formed from hundreds of glucose molecules joined to form a long chain part of a starch molecule 5 Proteins Proteins are made up of carbon, hydrogen and oxygen molecules but with the addition of nitrogen Carbohydrates are made up of glucose units. Proteins are made up of units called amino acids There are about 20 different amino acids. Examples are glycine (Gly), alanine (Ala), valine (Val) and cysteine (Cyst) The amino acids, Gly-Val-Val-Cyst-Ala-Gly-Ala-Val joined together would make a small protein Proteins make up the structure of cells; cytoplasm, nucleus cell membranes and enzymes 6 Protein structure and shape The way the amino acids join up, gives a protein molecule a particular shape, which is different for every protein Ser-Cyst-Val-Gly-Ser-Cyst Ala Val Val-Cyst-Ser-Ala-Ser-Cyst-Gly Val- Cyst-Ala-Ala-Ser-Gly This is a small, imaginary protein molecule showing how it acquires a shape High temperatures or certain chemicals can cause the protein molecule to lose its shape and its properties. 7 8 Lipids Lipids are fats and oils They are made up from glycerol and fatty acids Examples of fatty acids are stearic acid, oleic acid and palmitic acid H2 C O stearic acid H C O oleic acid H2 C O palmitic acid glycerol fatty acids A simple lipid Salts and water In addition to proteins, carbohydrates and lipids, cytoplasm contains salts and water Water makes up the bulk of cytoplasm All the chemical reactions in cytoplasm take place in solution, i.e. in water Water itself takes part in many of these chemical reactions Salts of sodium, potassium and calcium and many others play an important part in these reactions 9 Enzymes 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 10 Enzyme action (1) 11 Enzymes are large protein molecules Like all proteins, each enzyme molecule has a particular shape This shape determines which chemical reaction the enzyme can speed up In speeding up the reaction, the enzyme combines temporarily with the substances it is acting on Any substance an enzyme acts on is called a substrate 12 The substrate 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 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 The next sequence shows how an enzyme can 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 16 A ‘breaking-down’ reaction this is called the active site of the enzyme the shape of the substrate molecule fits the enzyme shape 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 substrate 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 + substrate enzyme denatured by heat denatured enzyme cannot combine with substrate 23 24 ENZYME ACTION 1 glucose molecules E 1. A glucose molecule combines with the active site on an enzyme 25 E 2 A region of the active site is still available 26 3 One end of a growing starch molecule combines with the glucose molecule at the active site E part of starch molecule 27 4 The growing starch molecule breaks free from the enzyme which is now free to repeat the reaction E 28 Enzyme action 11 glucose molecules E E 2 E E 3 E E part of starch molecule 4 29 Question 1 The correct formula for glucose is (a) C12H22O11 (b) C5H10O5 (c) C4H8O4 (d) C6H12O6 30 Question 2 Which is the most accurate description of a carbohydrate? A carbohydrate contains (a) carbon and oxygen (b) carbon, oxygen and nitrogen (c) carbon, hydrogen and oxygen (d) carbon and hydrogen 31 Question 3 When two molecules of glucose combine, they form (a) maltose (b) sucrose (c) fructose (d) ribose 32 Question 4 Which is the most accurate description of a protein Proteins contain (a) carbon, hydrogen and oxygen (b) carbon, hydrogen, oxygen and nitrogen (c) carbon, hydrogen and nitrogen (d) carbon, nitrogen and oxygen 33 Question 5 Which statements are correct? Proteins are present in (a) cell membranes (b) cell walls (c) cytoplasm (d) nucleus 34 Question 6 High temperatures damage proteins by (a) decomposing them (b) changing their chemical composition (c) changing their shape (d) making them soluble 35 Question 7 A protein is made up of a series of (a) glucose units (b) fatty acids (c) amino acids (d) carbohydrates 36 Question 8 Lipids are made up of (a) glycerol and amino acids (b) glycerol and fatty acids (c) protein and fatty acids (d) starch and fatty acids 37 Question 9 Enzymes are (a) proteins (b) lipids (c) carbohydrates (d) a combination of these 38 Question 10 An enzyme can (a) change a reaction (b) prevent a reaction (c) slow down a reaction (d) speed up a reaction 39 Question 11 A substrate is a substance which (a) an enzyme acts on (b) is produced by an enzyme reaction (c) is a particular kind of enzyme (d) is any chemical substance in a cell 40 Question 12 An enzyme can (a) combine with different substrates (b) form different kinds of end-product (c) function at temperatures above 90oC (d) speed up a reaction in the cytoplasm 41 Question 13 The part of an enzyme which combines with the substrate is called (a) the reaction centre (b) the active site (c) the action centre (d) the reaction site 42 Question 14 After being exposed to a high temperature an enzyme cannot function because (a) it has been broken down (b) its shape has been changed (c) its composition has been changed (d) it cannot separate from its substrate 43 ANSWER Correct 44 ANSWER Incorrect