Enzymes Flashcards
what 2 ways can a rxn be accelerated?
1) adding heat
-increaes number of reactants with sufficent energy
2) adding a catalyst
-decreases activation energy needed (doesn’t react)
what is the difference between an enzyme and a catalyst?
enzymes are catalysts but not all catalysts are enzymes
-enzymes are largely organic in nature and are bio-catalysts, while non-enzymatic catalysts can be inorganic compounds.
Neither catalysts nor enzymes are consumed in the reactions they catalyze.
True or False: enzymes are proteins
True however, there are a few exceptions
-typically globular proteins
what are characteristics of enzymes?
-accelerate rxn rates
-regenerate at the end of a rxn
-highly specific (no side rxns)
is enzyme structure flexible? why or why not?
since they are proteins, enzyme structure is flexible to an extent
what does changing the shape of an enzyme do?
change it’s function
-helps with regulation
How are some reactions able to proceed if the overall free energy is positive?
They aren’t
-in all systems a rxn will only proceed if the free energy of the products is less than the free energy pf the reactants
what determines the speed of a favourable biochemical rxn?
the size of the activation energy barrier
how do enzymes affect the free-energy change of a reaction?
They don’t!
-enzymes reduce the free energy of the TS
what 4 ways to enzymes contribute to the reduction of free energy for the TS?
1) removal of substrates from an (aq) solution
2) proximity and orientation
3) taking part in rxn
4) stabilizing the TS
what is an active site?
region of the enzyme where catalysis occurs
-small portion of the protein
what is located in the active site?
key amino acids
-binding and catalysis
what do active sites determine?
affinity, specificty and rate
what is the relation of the active site to the substrate/TS?
the active site is complementary to the substrate/TS
-shape, hydrophobic interaction, H-bonds and ion pairs
what 3 advantages does the exclusion of water provide in a rxn?
1) accelerates rxn
2) enhances polar interactions
3) prevents side rxn’s
what does an “induced fit” mean? why is it important?
the enzyme changes shape once bound to the substrate
-closes off active site (excludes more H2O)
-brings catalytic/reactive groups together
why is proximity and orientation an important factor in the enzyme active site’s function?
chemical rxn’s only occur if substrates come together in the right orientation and distance
how might an enzyme participate in a reaction?
they may work to position functional groups near the substrates in the active site
-acid/base catalysis
-covalent catalysis
-metal ion catalysis
this can be done through AA or cofactors
what are cofactors?
molecules/compounds that enhance the reactive potential of proteins by providing new reactive functional groups
what does binding the TS do to delta G?
it will help lower delta G of the TRANSITION STATE
what is involved in the interaction of transition state stabilization?
parts of the protein interact with the unstable TS
does the enzyme active site bind the substrate or the TS better?
the TS
what is michaelis constant?
The same as Kd; reflects affinity of enzyme for substrate
-small Km = high affinity = better substrate
what is a competitive inhibitor?
a substance that binds reversibly to the active site to physcially block active site
-resembles the substrate or TS but doesn’t react
what affect do competitive inhibitors have on affinity for enzyme and substrate?
they decrease affintiy (increase Km)
what is an allosteric enzyme?
enzymes that have an additional binding site for effector molecules other than the active site. The binding brings about conformational changes, thereby changing its catalytic properties.
how is alloesteric enzyme activity modulated?
by the non-covalent binding of specific molecules at a site other than the active site or at the active site
-heteroallostery vs homoallostery
what 2 states do allosteric enzymes have?
T state- low activity
R state - high activity
what state does an allosteric activator favour?
R state
what state does an allosteric inhibitor favour?
T state
what line represents an allosteric enzyme that has been inhibited?
green
what line represents an allosteric enzyme that has been activated?
blue
what is the most common type of reversible covalent modification?
phosphorylation
-may increase / decrease activity of the target enzyme
- may produce slight change in shape
what enzyme catalyzes the phosphorylation of proteins?
protein kinase
what enzyme catalyzes the dephosphorylation of proteins by hydrolysis?
protein phosphatases
is phosphorylated of enzymes a reversible or irriverisble reaction?
reversible
