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Enzymes

Enzymes. SBI 4U September 14 th , 2012. What are Enzymes?. Enzymes are …. Enzymes are proteins (tertiary or quarternary ) that catalyze (i.e., increase the rates of) chemical reactions. What is a Catalyst?.

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Enzymes

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  1. Enzymes SBI 4U September 14th, 2012

  2. What are Enzymes?

  3. Enzymes are … Enzymes are proteins (tertiary or quarternary) that catalyze (i.e., increase the rates of) chemical reactions

  4. What is a Catalyst? • A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change • In catalyzed reactions, the reactants are converted into products faster than they would be without the catalyst

  5. All reactions require Activation Energy • Activation Energy is defined as the energy that must be overcome in order for a chemical reaction to occur • Heat provides activation energy for most reactions

  6. Temperature is key! • Even though an increase in temperature is needed for most reactions to occur, too much heat can denature proteins, causing them to lose their function! • Therefore, catalysts allow reactions to proceed at suitable rates at moderate temperature by reducing the activation energy needed to catalyze reactions

  7. What does an enzyme act on? • An enzyme acts on a substrate • A susbtrate is the reactant that an enzyme acts on when it catalyzes a chemical reaction • The substrate binds to a particular site on the enzyme to which it is attracted

  8. Enzymes are very specific as to which substrate they bind to – they usually don’t bind to isomers of their substrate • The names of enzymes usually end in –ase. For example: amylase (found in saliva), lactase (found in small intestine)

  9. The Process of an Enzyme-Catalyzed Reaction • Substrate binds to the enzyme at the active site (located on the enzyme) • Substrate’s functional groups functional groups come close to the functional groups of a number of amino acids as the substrate approaches the active site. This allows the protein to change its shape, thereby better accommodating the structure – induced-fit model • The attachment of the enzyme’s active site creates the enzyme-substrate complex

  10. How do Temperature and pH affect Enzyme Activity? • Temperature – if temperature increases beyond the critical point, the protein structure can be disrupted and the enzyme can lose its function • Thus, every enzyme has an optimal temperature at which it works best • Ex: most human enzymes work best at normal body temperature 37 C, while those archaebacteria work best at above 100 C • Ph – Like temperature, enzymes work best at an optimal pH. Ex: Pepsin works best in an acidic environment with a Ph of 2

  11. Cofactors & Coenzymes • Cofactors “helper molecules” – non-protein compounds that are bound to a protein and required for the protein’s biological activity. Cofactors are usually enzymes themselves. Example: vitamins & minerals • Cofactors include zinc and manganese ions • Coenzymes – derivatives of vitamins. Also help with catalysis

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