chapter 4: 4.4 to 4.5

1. CHEMICAL COMPOSITION OF THE CELL 4.4 LIPIDS By: RumaizahMuhamad

2. LIPIDS Elements of lipids: Carbon Hydrogen Oxygen Some lipids contain: Phosphorus Nitrogen Insoluble in water. Soluble in: Other lipids and Organic solvents (eg; alcohol & ether)

4. Waterproof: prevent entry and evaporation of water

6. Including cholesterol and hormones

7. Eg: testosterone, estrogen and progesteroneTriglycerides

8. Fats & Oils Fats & oils are triglycerides * Each fatty acid consists of a long hydrocarbon chain with a different number of carbon atoms for different fatty acids.

9. Fatty Acids Saturated FATS Fats containing saturated fatty acids  saturated fats Unsaturated fats Fats containing unsaturated fatty acids  unsaturated fats

10. Fatty Acids Saturated fats Cannot form any chemical bond with other atoms. All the bonds between the carbon atoms have maximum number of H atoms. Eg: butter (solid at RT) Unsaturated fats Carbon atoms in hydrocarbon chain are not bonded to the maximum number of H atoms. One double bond  monounsaturated fats Two/ more double bond  polyunsaturated fats. Eg: corn oil (liquid at RT)

11. TEST YOURSELF Tick (√) if the statement is true. Lipids contain oxygen, hydrogen and carbon [ ] Fats and oils are triglycerides [ ] A triglyceride has one glycerol and three fatty acids [ ] Saturated fats are liquid at room temperature [ ] Unsaturated fats are essential to good nutrition[ ]

12. 4.5 ENZYMES Enzymes are biological catalyst that regulate almost all the cellular reactions. It is needed in life processes to regulate biochemical processes in the cells  metabolism.

13. Characteristics of Enzymes Enzymes are proteins: synthesized by living organisms. In enzymatic reactions: Alter/ speed up the rates of chemical reactions but remain unchanged at the end of reactions.

15. Cont. Activity of enzymes can be slowed down or completely stopped by inhibitors. Eg: Lead, mercury To function well, enzymes require helper molecules called cofactor. Eg: organic cofactor are derivatives of water-soluble vitamins such as Vit.B. Inorganic cofactors: ferum and copper

16. Naming of Enzymes Named according to the name of the substrate it catalyses. Adding suffix –aseat the end of the name of their substrate. Eg: Other enzymes were named before a systematic way of naming enzymes. Eg: pepsin, trypsin and rennin.

17. The Sites of Enzyme Synthesis Enzymes are proteins, therefore ribosomes are also the sites of enzyme synthesis. Information for enzyme synthesis is carried by DNA. Different sequences of bases in the DNA are coded to make different proteins. During the process, messenger RNA is formed to translate the codes into a sequence of a.acids. These a.a are bonded together to form specific enzymes according to DNA’s codes.

18. Intracellular Enzymes Intracellular enzymes: enzymes which are synthesized and retained in the cell for the use of the cell itself. Found in cytoplasm, nucleus, mitochondria, chloroplast Eg: oxidoreductase catalyses biological oxidation and reduction in mitochondria.

19. Extracellular enzymes Extracellular enzymes: enzymes which are synthesized in the cell but secreted from the cell to work externally. Eg: digestive enzymes  produced by the pancreas but are transported to the duodenum (the site for enzyme action). Production of extracellular enzymes.  Refer to topic 2.3, appreciating the uniqueness of the cell.

20. TEST YOURSELF! List down 5 characteristics of enzyme operations. ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ Define: Intracellular enzymes Extracellular enzymes

21. Mechanism of Enzyme Action Polypeptide chains of enzyme folded into a three-dimensional shape includes a ‘pocket’ called ACTIVE SITE. Active site  complements its substrate (substrate must fit enzyme precisely). The mechanism of enzyme action can be explained by the ‘lock and key’ theory.

22. Lock Key The ‘lock and key’ hypothesis of enzyme action

23. Factors Affecting Enzyme Activity Temperature pH Substrate concentration Enzyme concentration

24. Effects of TEMPERATURE Low temperature (T): enzyme-catalyzed reaction takes place slowly. Increase temperature: Reaction between substrate and enzyme accelerated. For every 10⁰C rise in T, rate of reaction is doubled. Optimum T: temperature at which enzyme catalyses a reaction at the maximum rate. Human : 37⁰C Plants : 25⁰C Beyond optimum T : enzymes lose their activities and denatured.

26. Beyond optimum T No longer increase rate of reaction. The bonds that hold enzyme molecules together begin to break at high T. Thus, destroying active site. Denaturation is irreversible.

27. TEST YOURSELF! Question 1 – 6. Tick (√) if the statement is true. All enzymes are proteins [ ] Most intracellular enzymes work best in neutral conditions. [ ] Extracellular enzymes work inside the cell [ ] The reaction of enzymes takes at the active site in the enzyme molecule. [ ] The rate of enzyme reaction depends on the temperature and light intensity. [ ] Enzymes are destroyed by heat because enzymes, being proteins, are denatured at high temperature. [ ] The way a substrate’s molecule fits into an enzyme’s _________ is explained by the lock and key hypothesis. The enzyme is the ____________ and the substrate is the _____________. The enzyme activity is influenced by __________, ____________, ______________ concentration and enzyme concentration.

28. Effects pH on enzymes Sensitive to the changes of pH. Optimum pH : pH at which the rate of reaction is at the maximum/ fastest. Eg: Pepsin  function in acidic condition (pH2) in stomach Trypsin  function in alkaline condition (pH8.5) in duodenum.

29. A change in pH: Alter the charges on active sites and substrate surface Reduce ability of both molecules to bind with each other. Effects of pH on enzymes : reversible. When pH in environment reverts to optimum level, the ionic charges on active sites are restored. Thus, the enzymes resume their normal function.

31. Effects of substrate concentration Increase [substrate] : More substrate available to bind to the active site. Increase collisions between substrate and enzyme molecules. More products will be produced.

32. Rate of reaction : directly proportional to [substrate] until reach a maximum rate.

33. Effects of enzyme concentration When [enzyme] increase: more enzymes available. more active sites for catalytic reaction. Rate of reaction: increase if only there is abundant supply of substrate and other factors (pH, T, pressure and constant). Proportional to [enzyme]

35. The Use of enzymes Enzyme technology: the use of enzymes in industrial processes. By using your textbook and reference book, please find the examples of enzymes used in industries.

36. The importance of Chemical Composition in Cells