Enzymes

Role of enzymes

  • Enzymes catalyse specific chemical reactions
  • Enzymes are a globular protein with a tertiary structure
  • Reactions that enzymes catalyse are reversible
  • Enzyme activity is affected by several factors:temperature, pH, enzyme concentration+substrate concentration
  • Intracellular enzymes: catalyse reactions within cells
  • Extracellular enzymes: catalyse reactions outside of cells
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Mechanism of enzyme action: active site+specificit

  • Active site of an enzyme is complementary to the specific substrate molecule. Other molecules do not fit into the active site: enzyme cannot catalyse them.
  • Different levels of specificity: some enzymes are specific to 1 substrate and some are less specific=catalyse a no.of reactions.
  • Enzyme combines with substrate=enzyme-substrate complex: two ideas how interact with the substrates: lock and key, induced-fit
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Lock and key hypothesis

  • Substrate exactly fitting into the active site=lock and key hypothesis
  • Interactions between the R groups of the active site and substrate stabilise the enzyme= substrate altered= enzyme-product complex
  • Enzyme release this product and is free to accept another substrate molecule

Related image (http://3ppp.info/wp-content/uploads/2018/08/lock-key-model-denaturation-of-enzymes-lock-and-key-example-explain-the-difference-between-lock-and-key-model-and-induced-fit-model.jpg)

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Induced-fit hypothesis

  • Active site does not have a complementary shape to the substrates until it has moulded around the substrates so the are closer together.
  • Amino acids in the active siteare brought closer to the substrate to hold it in place+put the substrate under strain. This causes the reaction to proceed to form the product.

Related image (http://3ppp.info/wp-content/uploads/2018/08/lock-key-model-denaturation-of-enzymes-lock-and-key-example-explain-the-difference-between-lock-and-key-model-and-induced-fit-model.jpg)

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Activation energy

  • Activation energy: energy needed to overcome a barrier to allow reaction to occur.
  • The energy barrier may be overcome by increasing the temperature, pressure or adding a catalyst.
  • Enzymes provides an alternative pathwath with a lower activation energy.

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Determining initial rates of reactions

Image result for enzymes calculating initial rate of reaction graph

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Factors effecting enzyme activity: temperature

Image result for enzyme temperature graph (http://www.bbc.co.uk/staticarchive/199acbfe2bac854818d719d6ce0e53e4cd3cd5d2.gif)

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Factors effecting enzyme activity: temperature coe

  • Temp coefficient: ratio between activities of a process, such as an enzyme-catalysed reaction, at two temperatures.

Image result for temperature coefficient enzymes

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Factors effecting enzyme activity: pH

  • pH: measure of the concentration of H+ ions in solution.
  • Enzymes function at an optimum pH, above and below this pH the enzyme does not perform as well.
  • The optimum pH is specific for each enzyme, the pH range for some enzymes is larger than others.
  • Shape of the active site is dertimined by interactions: H + ionic bonding between R groups of the amino acids in the active site.
  • As H+ ion concentration changes, some of the bonds break= active site is less effective=complementary shape is lost= substrate cant bind to active site
  • The charges on R groups are important in formation of enzyme-substrate complex. Therefore, any changes to the charge will affect the ability of the active site to successfully bind to the substrate molecules.
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Factors effecting enzyme activity: pH

The graph shows:

  • Each enzyme is active over a range of pH
  • As pH increases the activity of each enzyme increases until a maximum is reached.
  • Maximum activity occurs at the optimum pH for each enzyme.
  • At values of pH above optimum temperature, activity decreases.
  • At certain ph there is no activity.

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Factors effecting enzyme activity: substrate conce

  • Substrate concentration determines the probability of collisions occuring between substrate and enzyme molecules.
  • Lower substrate concentration: fewer substrate molecules in solution=fewer will collide+form an enzyme substrate complex, rate of reaction is slower.

Image result for enzymes substrate concentration (http://www.rsc.org/Education/Teachers/Resources/cfb/images/07D.jpg)

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Factors effecting enzyme activity: enzyme concentr

  • Increased enzyme cocentration: higher availability of active sites=more enzyme-substrate molecules will form.
  • Consequently, the rate of reaction will rise until other factors become limiting: substrate concentration, pH and temperature.

Image result for enzyme concentration graph (http://www.rsc.org/Education/Teachers/Resources/cfb/images/07C.jpg)

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