Enzymes Flashcards
Catalysts
do not impact thermodynamics of the biological reaction (deltaHrxn, deltaG and equilibrium position)
they help the reaction go at a faster rate
lower activation energy
not changed/consumed
are pH and temp sensitive
reaction specific
Enzyme Specificity
a given enzyme will only catalyze a single reaction/class of reactions
Oxidoreductases
catalyze oxidation-reduction reactions (transfer electrons)
Cofactor: NAD+/NADP+
reductant: electron donor
oxidant: electron acceptor
Transferases
catalyze the movement of a functional group from onemolecule to another
Kinases are a form of ____ which catalyze the ______ to another molecule.
transferase
transfer of a phosphate group from ATP to another molecule
Hydrolases
catalyze the breaking of a compound into two molecules by ADDING water
named for their substrate (what they cleave)
Lyases
catalyze the cleavage of a single molecule into two products
DO NOT REQQUIRE WATER OR ACT AS OXIDOREDUCTASES
can do both breaking into two or building into one (synthases)
Isomerases
catalyze the arrangement of bonds within a molecule, specifically stereoisomers and constitutional isomers
can be classsidied as oxidoreductases, transferases or lyases
Ligases
catalyze the addition/synthesis reactions between large similar molecules and require ATP
nucleic acid synthesis
Endergonic Reaction
requires energy input (delta G > 0) betweej produce/reactant
Exergonic
energy is given off (delta G < 0) between product/reactants
Activation Energy
catalysts lower this to make it easier for the substrate to reach the transition state.
Enzymes may act to provide a _______ in terms of charge pH, stabalize _______ or bring reactive groups near to each other in the active site.
favorable microenviornment
stabilize transition state
Formation of the _______ complex in the ____ of an enzyme is the key catalytic activity of the enzyme, which reduces the _____ of the reaction.
enzyme-substrate
active site
activation energy
_____ , ______, and ______ within the active site all stabilize this spatial arrangement and increase efficiency of the enzyme.
hydrogen bonding, ionic interactions, transient covalent bonds
Lock and Key Theory
enzymes active site is already in appropriate conformation for the substrate to bind, no alteration of the substrates/enzyme structure is required
Induced Fit Model
endergonic and requires energy where substrate goes to active site and the shapes are altered to induce a fit and allow for correct binding to the site
Cofactos and coenzymes bind to the ______ of the enzyme and participate in the ____ of the reaction and are recruited only when needed.
active site
catalysis
Apoenzymes/Holoenzymes
enzymes without their cofactors
enzymes containing them
Prosthetic Groups
tightly bound cofactos or coenzymes necessaryfor enzyme function
Cofactors
inorganic molecules/metal ions often ingested
Coenzymes
small organic groups such as NAD+, FAD, CoA
water soluble vitamins like B complex and C
Fat soluble vitamins, ______, are better regulated by partition coefficients which quantify the ability of a molecule to dissolve in ____ vs ______ environment.
A, D, E, K
polar
non polar
Metabolic reactions often require _____, NAD+ (derived from _____) and biotin (derived from ______ )
magnesium
B3
B7
The concentrations of substrate and enzyme greatly affect how ____ a reaction occurs.
quickly
The only way to increase Vmax is by ____ the ____ concentration.
increasing
enzyme
Michaelis-Menten
describes the rate of reaction depends on concentration of both enzyme and substrate to form product
V =( vmax*[S] ) /( Km + [S] )
When v = 1/2 (reaction rate) vmax, then Km ___ [S]
equals
Km
the substrate concentration at which half the enzymes active sites are full
it is the Michaelis constant
intrinsic property
When comparing two enzymes, the one with the higher Km has the ______ for its substrate as it requires a _____ to be half saturated.
lower affinity
higher substrate concentration
When substrate concentration is ___ than Km, changes in substrate concentration will greatly affect the reaction rate.
At high substrate concentrations exceeding Km, the reaction rate increases much slowly as it approaches vmax, meaning it is ____ of substrate concentration
lower
independent
Lineweaver-Burk Plots
x-intercept : - 1/Km
y intercept = 1/vmax
useful when determining the type of inhibition of an enzyme as vmax and Km can be compared properly
Cooperative Enzymes
sigmoidal shape when looking at v vs. substrate concentration
multiple subunits and active sites
T and R states
Low affinity T state (tense)
High Affinity R state (relaxed)
binding of substrate encourages transition of other T subunits to R state to increase substrate binding to the other
loss of substrate can cayse R to T state transition and cause other subunits to go back to T state
Enzymes showing cooperative kinetics are often _______ in pathways like phosphofructokinase-1 in glycolysis.
regulatory enzymes
The activity of an enzyme is heavily influenced by its environment, in particular:
temperature
pH
salinity
Affect of Temperature on Enzymes
enzyme catalyzed reactions tend to double for every 10 degree celsius increase until optimum temperature is reached (in human body this is 37 degrees or 98.6)
at higher temperatures the enzyme will denature. Some enzymes may regain function at cooler temperatures.
Affect of pH on Enzymes
affects ionization of the active site ad can lead to denaturation of the enzyme
optimal pH is 7.4 (blood pH)
Exceptions to the physiological pH are in the ______ for Pepsin at pH 2 in the _____ and ______ which work around 8.5
digestive tract
stomach
pancreatic enzymes
Affect of Salinity on Enzymes
cam change enzyme activity in vitro by disrupting H and ionic bonds and partial change in conformation of enzyme…leading to denaturing
Feed-Forward
less often, enzymes are regulated by intermediates preceding the enzyme in pathway
Negative Feedback
feedback inhibition
once enough of a given product is made, pathway is turned off to prevent too much product being made
product may bind to the active site of an enzyme to inhibit them
Competitive Inhibition
involves occupancy of the active site
can be overcome by adding more substrate so it out numbers the amount of inhibitor
Vmax = same
Km INCREASES as mroe substrate is required
both intersect at the y-axis
noncompetitive Inhibitiron
bind to an allosteric site instead of active site to change enzyme conformation
cannot be overcome by adding mroe substrate as it is non competitive
bind equally to Enzyme and ES complezes unlike mixed inhibitors
vmax DECREASES as less enzyme avialble
Km = same as affinity for Substrate by enzymes unaffected is the same
intersect at x -axis on left hand plane
Mixed Inhibition
inhibitor binds to either E or ES but has a different affinity for each
bind at allosteric site
If prefer E state: Km INCREASES (lower affinity)
If prefer ES state: Km DECREASES (higher affinity)
vmax is decreased
intersect not on the axis
Uncompetitive Inhibition
bind only to the ES complex and lock the substrate to the Enzyme
afinnity for substrate is increased
bind at allosteric site
lowers Km and Vmax
parallel lines
Irreversible Inhibition
active site is made unavailable for a long time or the enzyme is permanently altered
Allosteric Enzymes
have multiple binding sites
alternate between active and inactive form
molecules that bind to allosteric site are allosteric activators/inhibitors that cause a conformational shift that either makes active site more readily available or less available.
Covalently Modified Enzymes
activated/deactivated by phosphorylation/dephosphrylation
glycosylation by attaching sugar moieties
Zymogens
Enzymes that are not tightly controlled are secreted as inactive zymogens which contain a catalytic and regulatory domain. Once regulatory domain is altered or removed, then active site is exposed for function
-ogen ending
apoptotic enzymes have similar regulation
