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
active site of chymotrypsin
is hydrophobic and open therefore it binds buly hydrophobic residues
trypsin active site
has a negatively charged Asp, therefore it binds positively charged molecules
Elastase active site
has a Val and Thr which narrow the crevice of the active site, only allowing small amino acids such as Gly, Ala, and Val to bind
Energy stored in ATP
There are two possible high energy bond cleavages in ATP
- ATP to ADP and ADP to AMP
- this releases about 13 kcal/mol
