Upload
gotzon
View
93
Download
0
Tags:
Embed Size (px)
DESCRIPTION
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?. - PowerPoint PPT Presentation
Citation preview
EnzymesSBI 4U
September 14th, 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? 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
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
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
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
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)
The Process of an Enzyme-Catalyzed Reaction1. Substrate binds to the enzyme at the active
site (located on the enzyme)2. 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
3. The attachment of the enzyme’s active site creates the enzyme-substrate complex
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
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