Enzyme Catalysts Flashcards
Enzyme complications in cystic fibrosis
-treatment
-a neutrophil mediated inflammatory response releases elastase which contributes to lung destruction -blockage of the pancreatic ducts leads to insufficient digestive pancreatic enzymes which leads to malabsorption of fat
and proteins
-treatment: nebulized antibiotics and supplemental enzymes
oxidoreductases
oxidation-reduction reactions
transferases
transfer of a chemical group
hydrolases
lysis by water
lyases
a cleavage reaction not using water
isomerases
change of molecular confirmation
ligases
joining of two compounds
serine proteases
- proteolytic enzymes that catalyze peptide bond hydroplysis
- include pancreatic enzymes: chymotrypsin, trypsin, elastase, adn neutrophil elastase
Specificity of serine proteases
-not only specific for binding peptides, but also have specificity pockets for preferantially binding certain amino acids
active site
- usually a crevice on the surface of the enzyme
- comprises amino acids that bind the substrate and those that catalyze the reaction
summary of mechanism for serine protease
- correct substrate is bound in the correct orientation (serine is made unusually reactive)
- attack by a serine
- oxyanion formed in the transition state is stabilized by the enzyme
- product release
Gibbs Free Energy (delta G)
- intrinsic energy to certain compounds.
- a drop indicates that a more stable form has been achieved
- spontaneous reactions have a negative delta G, reactions that flow in the opposite direction have a positive
- sensitive to concentration of reactants and products
- standard conditions: certain temp, 1M concentrations except for H+ (ph=7)
at equilibrium, Q=
When Q>Keq
When Q
Keq
the reaction goes in reverse
the reaction moves forward
when delta G =0
the reaction is in equilibrium
differences between biochemical and chemical reactions
- reactions in the body are not in equilibrium, we are burning fuel to keep it this way
- removing product can shift equilibrium
- reactions in the bod proceed under very non-standard conditions
the free energy of activation
-enzymes role
- the amount of energy necessary to put into a reaction toget it to go a certain way
- this is the change in energy between the reactant (substrate) and the transition state
- enzymes act to reduce the energy of the transition state,
stabilization of the transition state by a catalyst
- lowers the activation barrier, increasing the attainment of equilibrium
- catalyst does not change the free energy of the substrate of product
- does not alter the equilibrium ratio
catabolism vs anabolism
- catabolism burns fuel to generate ATP
- anabolic: burning ATP for biosynthetic processes, active transport, or mechanical work
coupled reactions
- enzymes will couple the hydrolysis of ATP with another, less favorbale reaction
- this uses the energy produced from ATP hydrolysis to drive the other reaction
example of a coupled reaction
- hexokinase uses hydrolysis of ATP to add a phosphate to glucose, creating glucose-6-phosphate
- if you sum the delta G’s, it comes up negative, suggesting the forward reaction is favored overall.
enzyme velocity
-the amount of product formed per unit time
Km
- the concentration of substrate that it takes to reach half of Vmax
- this does not change with the addition of more substrate
- larger Km’s reflect a lower enzyme to substrate affinity
Vmax
- this is the maximum amount of product per unit time that a certain amount of enzyme can pump out.
- Vmax is directly proportional to the amount of enzyme present
Lineweaver Burk plot
-y and x intercepts
- this is a linear plot
- also known as the double reciprocal plot
- 1/v=(Km/Vmax) 1/[S]+1/Vmax
- y intercept = 1/Vmax
- x intercept = -1/Km
