Enzymes Flashcards
Do enzymes impact the thermodynamics of a biological reaction?
No, delta H_rxn and the equilibrium position do not change
What do enzymes do?
- Lower the activation energy
- Increase the rate of the reaction
- Are not changed or consumed in the reaction (will appear in the reactants and the products)
- Are pH and temperature sensitive, optimal activity at specific pH ranges and temperatures
- Do not affect the overall deltaG of the reaction
- Are specific for a particular reaction or class of reactions
Oxidoreductases?
Catalyze oxidation-reduction reactions, transfer electrons between biological molecules, often have cofactors that serve as electron carriers, like NAD+ or NADP+; electron donor = reductant; electron acceptor = oxidant
transferases?
catalyze the movement of a functional group from one molecule to another, ex. kinases
kinases?
catalyze the transfer a phosphate group, generally from ATP, to another molecule
Hydrolases?
Catalyze the breaking down of a compound into two molecules using the addition of water, ex. phosphatase, cleaves a phosphate group from another molecule
Lyases?
Catalyze the cleavage of a single molecule into two products, don’t require water, don’t act as oxidoreductases, can also catalyze the reversal (two molecules into a single molecule), in that case would be called a synthase
LIL’HOT
Major enzyme classifications
- Ligase
- Isomerase
- Lyase
- Hydrolase
- Oxidoreductase
- Transferase
Isomerases?
Catalyze the rearrangement of bonds within a molecule, can catalyze reactions between stereoisomers as well as constitutional isomers
Ligase?
Catalyze addition or synthesis reactions, generally between large similar molecules and often require ATP, often with nucleic acid synthesis and repair on Test Day
Endergonic reaction?
One that requires energy input, deltaG>0
Exergonic reaction?
One where energy is given off, deltaG< 0
If a reaction is spontaneous, deltaG is
negative
How do catalysts impact activation energy?
They lower it
The molecule upon which an enzyme acts is known as its…?
Substrate
The location where the substrate is held during its chemical reaction is known as the
active site
Lock and Key Model
suggests that the enzyme’s active site is already in an appropriate conformation for the substrate (key) to bind
Induced Fit Model
More scientifically accepted theory, substrate and enzyme active site don’t seem to fit, but then they do
Enzymes without their cofactors are called
apoenzymes
Enzymes with cofactors are called…
holoenzymes
Tightly bound cofactors or coenzymes that are necessary for enzyme function are called…
prosthetic groups
A rate of reaction can’t go faster once it has reached
Saturation, max velocity= v_max
What does K_m represent?
The substrate concentration at which half of the enzyme’s sites are full, 1/2 V_max
cofactors
small, metal cations
coenzymes
small, organic molecules
temp. impact on enzymatic reactions?
tend to double in velocity for every 10 degrees C, eventually will denature at higher temps
pH impact on enzymatic reactions?
body works best at certain pHs
salinity impact on enzymatic pHs?
altering the concentration of salt can change enzyme activity in vitro, can change conformation of the enzyme, sometimes cause denaturation
negative feedback
helps maintain homeostasis, once we have enough of a given product, we turn off the pathway that created that product
feed-forward regulation
enzymes may be regulated by intermediates that precede the enzyme in the pathway
competitive inhibition?
involves occupancy of the active site, doesn’t alter V_max, because if enough substrate is added, it will outcompete the inhibitor and be able to run the reaction at max velocity, K_m increases
noncompetitive inhibitors?
bind to an allosteric site instead of the active site, which induces a change in enzyme conformation, decreases V_max, doesn’t change Km
Mixed inhibition?
inhibitor can bind to enzyme or the enzyme-substrate complex, different affinity for each, bind at the allosteric site, decrease V_max, can increase or decrease Km
Uncompetitive inhibtion?
bind only to the enzyme-substrate complex, decrease Km and decrease vmax
allosteric activator?
an activator will result in a shift that will make the active site more available for binding to the substrate by binding to the allosteric site
allosteric inhibitor?
will make the active site less available for binding to the substrate by binding to the allosteric site
allosteric sites
a site that can regulate the availability of the active site that’s not the active site
Glycosylation
the covalent attachment of sugar moieties, another covalent enzyme modification
enzyme can be activated or deactivated by…
phosphorylation or dephosphorylation (covalent modification with phosphate)
zymogens
inactive forms of enzymes (like ones for the stomach), often have the suffix -ogen
irreversible inhibtion
alters the enzyme in such a way that the active site is unavailable for a prolonged duration or permanently; new enzyme must be synthesized for the reaction to occur again
cooperative enzymes
display a sigmoidal curve bc of the change in activity with substrate binding
