3.5

• Extremophiles


  • Organisms that live in the most extreme environments
  • Many extremophiles are prokaryotes
  • Their enzymes have chemical adaptations enabling them to function in extremes of saltiness, high temperature, and cold
• Extremophiles


  • Enzymes from extremophile bacteria that live in hot springs used in polymerase chain reaction (PCR)
• PCR is a key process in DNA fingerprinting and genome analysis
• In an extreme environment, such as the hot springs found in Iceland, it is amazing that any enzymes function at all
• A container of milk left at the back of your fridge for a week or two will be disgusting. The milk will go off as enzymes in bacteria break down the protein structure
• Leave your milk in the sun for a day and the same thing happens - but much faster. Temperature affects the rate at which chemical reactions take place, even when they are controlled by biological catalysts
• Biological reactions are affected by the same factors as any other chemical reactions. These factors include concentration, temperature, and surface area
• In living organisms, an increase in temperature only increases the rate of reaction up to a certain point
• Enzyme-controlled reactions


  Reactions that take place in cells at relatively low temperatures
• As temperature increases


  The rate of enzyme-controlled reactions increases
• For most organisms, this is only true up to temperatures of about 40 °C
• Denatured


  The protein structure of the enzyme is affected by the high temperature, the long amino acid chains begin to unravel, and as a result, the shape of the active site changes
• The substrate will no longer fit in the active site. The enzyme can no longer act as a catalyst, so the rate of the reaction drops dramatically
• Most human enzymes work best at 37°C, which is human body temperature
• Without enzymes, none of the reactions in your body would happen fast enough to keep you alive
• It is dangerous if your temperature goes too high when you are ill. Once your body temperature reaches about 41 °C, your enzymes start to be denatured, which will result in death
• Not all enzymes work best at around 40°C. Bacteria living in hot springs survive at temperatures up to 80°C and higher
• Some bacteria that live in the very cold, deep seas have enzymes that work effectively at 0°C and below
• pH


  A change in pH affects the forces that hold the folded chains of the enzyme in place, changing the shape of the active site
• Different enzymes work best at different pH levels. A change in pH can stop them working completely
• Plotting graphs


  1. Choose your scale carefully

  2. Label your x and y axes carefully

  3. Make sure you show the units on your labelled axes

  4. Plot each point as accurately as possible

  5. Draw the line of best fit through your points
• The rate of reaction at any given time is found by calculating the gradient of the tangent drawn at that point on the line