CHEMICAL COMPOSITION OF THE CELL

1. General properties of enzymes.
   
   • i) Enzymes are proteins produced by living cells.
     
   • ii) Enzymes are biological catalysts which speed up the rate of biochemical reactions.
     
   • iii) Enzymes are not destroyed at the end of a reaction.
     
   • iv) Enzyme-controlled reaction is irreversible
     
     • Example : lactose + water , glucose + galactose
       
   • v) Enzymes are sensitive to changes in temperature, and are very active at an optimum temperature of 40°C. Enzymes are denatured at high temperature .
     
   • vi) Enzymes are sensitive to changes in pH of medium.
     
   • vii) Enzyme action is very specific, One type of enzyme can catalyse only one type of substrate.
2. The figure represents the action of an enzyme.
   
   
   • a) State two properties of enzyme illustrated by the above figure.
     
     • Enzymes action is very specific.
     • Enzymes are not destroyed by the reaction they catalysed.
       
   • b) Name two digestive enzymes, their substrate and products.
     
     • Enzyme : Amylase, Substrate : Starch, Products: Maltose.
     • Enzyme : Trypsin, Substrate : Polypeptides, Products: dipeptides.
       
   • c) Figure below shows the relationship between enzyme activity and temperature. Complete the line to show the effect of increasing the temperature from 10°C to 60°C.
     
   • d) Uses of enzymes.
     
     

     Enzymes	Usage types	Effect
     Protease	Leather Industry	Remove hairs from skin
     Papain//Protease	Digestion	Tenderise meat
     Cellulase	Industrial use	Softening vegetables, removing seed coats
     Protease//Lipase	Daily use	Add to washing powder to remove protein stains
     Lipase	Digestion	Convert fat to fatty acids and glycerol
     Amylase	Digestion	Convert starch to maltose

3. The figure shows an experiment set-up to investigate the effect of pH on enzyme activity. Enzyme Q is found inside the mammalian digestive system.
   After 24 hours, the following results were obtained:
   

   pH	Reduction in length of egg white strip (mm)
   1	7
   2	9
   3	6
   4	3
   5	1
   6	0

   
   
   • a) Using the results in the table, plot a graph to show the reduction in length of the egg white strip against pH of the medium.
     
     • P – axis with scales ----1
     • T – points plotted accurately ------ 1
     • B – shape of line – smooth, single curve ------1
   • b) Explain the observed reduction in the length of the egg white strip.
     
     • Increasing the pH value of the medium will decrease the action of enzyme Q on egg white. The optimum pH of enzyme Q is 2. Enzyme Q works at its maximum rate at this pH/ At this pH, the reduction of length of the egg white strip is the greatest.
   • c)
     
     • Name enzyme Q and the products of its action on egg white.
       
       • Enzyme Q : Pepsin,
         Products: Polypeptides / Peptones
     • Which part of the mammalian digestive system produce enzyme Q?
       Stomach.
4. Below shows the structures of four organic compounds which are found in living cells.
   
   
   
   • a)
     
     • i) Name the structures of compounds X and Z.
       
       • X : Protein/ polypeptide.
         Y : triglyceride/ lipid.
     • ii) State the monomer of X and Y.
       
       • X : amino acid.
         Y : glucose.
   • b) What would happen if pancreatic cells unable to synthesis compound X?
     
     • Enzymes / any pancreatic enzyme / hormones /any pancreatic hormone cannot be synthesised.
   • c)
     
     • i) In the space below draw and label the structure of the basic unit of organic compound W.
       
     • ii) Name two types of organic compound W.
       
       • DNA & RNA.
     • iii) State two structural differences between the organic compounds you have named in (c)(ii).
       
       
       • DNA consists of two/double strands polynucleotide but RNA consists of a single / one strand of polynucleotide.
         
       • Strands of polynucleotide in DNA are twisted (around each other) / in a form of double helix but strand of polynucleotide in RNA is linear.
         
       * reject: molecules of DNA is big but molecules of RNA is small