The Chemicals of Living Cells

1. The Chemicals of Living Cells ©The Wellcome Trust

2. 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.

3. 3 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

4. 4 C C O C C C C Glucose C6H12O6 C HO HO C H C HO H H OH C 5 of the carbon atoms may be arranged in a ring H OH C C H2OH A glucose molecule as a straight chain This molecule is often represented simply as a hexagon

5. 5 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 Starch and cellulose are formed from hundreds of glucose molecules joined to form a long chain maltose part of a starch molecule

6. 6 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

7. 7 Ser-Cyst-Val-Gly-Ser-Cyst Ala Val Val-Cyst-Ser-Ala-Ser-Cyst-Gly Val- Cyst-Ala-Ala-Ser-Gly Protein structure and shape The way the amino acids join up, gives a protein molecule a particular shape, which is different for every protein 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.

8. 8 H2 C O A simple lipid H C O H2 C O glycerol 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 stearic acid oleic acid palmitic acid fatty acids

9. 9 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

10. 10 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

11. 11 Enzyme action (1) 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. 12 substrate A substrate B The substrate molecules fit the shape of the enzyme enzyme

13. 13

14. 14 substrates combine temporarily with enzyme enzyme joins substrates together

15. 15 enzyme unchanged and ready for next reaction new compound released by enzyme

16. 16 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

17. 17 the shape of the substrate molecule fits the enzyme shape A ‘breaking-down’ reaction this is called the active site of the enzyme

18. 18 Intermediate stage (1) substrate combines temporarily with enzyme enzyme will break molecule here

19. 19 Intermediate stage (2) substrate splits and separates from enzyme

20. 20 Final break-down products enzyme ready for next reaction end-products

21. 21 Enzymes can act on only one type of substrate Denaturing involves a change of shape in the enzyme molecule so that it cannot combine with the substrate Properties of enzymes 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 Individual enzymes work best at a particular temperature and pH (acidity or alkalinity)

22. this substrate this substrate 22 Enzymes can act on only one type of substrate cannot combine with this enzyme cannot combine with this enzyme

23. 23 enzyme denatured by heat denatured enzyme cannot combine with substrate Because enzymes are proteins, they are denatured by heat or some chemicals enzyme + substrate

24. 24 ENZYME ACTION 1 E glucose molecules 1. A glucose molecule combines with the active site on an enzyme

25. 25 E 2 A region of the active site is still available

26. 26 part of starch molecule E 3 One end of a growing starch molecule combines with the glucose molecule at the active site

27. 27 E 4 The growing starch molecule breaks free from the enzyme which is now free to repeat the reaction

28. 28 1 1 E 2 E part of starch molecule glucose molecules E 3 E E E 4 Enzyme action

29. 29 Question 1 The correct formula for glucose is (a) C12H22O11 (b) C5H10O5 (c) C4H8O4 (d) C6H12O6

30. 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. 31 Question 3 When two molecules of glucose combine, they form (a) maltose (b) sucrose (c) fructose (d) ribose

32. 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. 33 Question 5 Which statements are correct? Proteins are present in (a) cell membranes (b) cell walls (c) cytoplasm (d) nucleus

34. 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. 35 Question 7 A protein is made up of a series of (a) glucose units (b) fatty acids (c) amino acids (d) carbohydrates

36. 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. 37 Question 9 Enzymes are (a) proteins (b) lipids (c) carbohydrates (d) a combination of these

38. 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. 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. 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. 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. 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. 43 ANSWER Correct

44. 44 ANSWER Incorrect