Module 2 Flashcards
Mammals cannot synthesize all coenzymes from scratch
A tightly bound metal or coenzyme is a ________
An apoenzyme plus a prosthetic group is a ________ .
prosthetic group
holoenzyme
ΔGo = \_\_\_\_\_\_\_\_\_\_\_\_\_\_ ΔG'o = \_\_\_\_\_\_\_\_\_\_\_\_\_\_
standard free energy change (298 K, 1 atm, 1 M)
biochemical standard free energy change (pH 7)
Enzymes do not alter the equilibrium between Sand P only the _________ __ ___ _________
rate of the reaction
Just because ΔG’ois negative does not mean that the reaction will take place at a detectable rate
Even though ΔG’ois very negative sucrose is very stable
Catalysts enhance reaction rates by lowering _______ _______
activation energies
______ ______:any species along a reaction pathway with finite chemical lifetime(longer than a molecular vibration ~10-13seconds)
Reaction intermediates
Reaction equilibria are linked to ____ (standard free energy change)
Reaction rates are linked to ΔG‡ (activation energy)
ΔG’o
ΔG‡
K’eq = [P]/[S]
ΔG’o= -RT ln K’eq
R, 8.315 J/mol•K
T, absolute temp in K
Keq and ΔG’o relationship
First order reaction: __ = __ * __
Second order reacion: __ = __ __ __
V=k[S]
V=k[S1]{S2}
How do enzymes speed up the rate of reactions?
- formation of covalent interactions with amino acid side chains or bound metals or cofactors
- non-covalent interactions (formation of EScomplex)
binding energy, ΔGB,is a major source of free energy used by enzymes to lower the activation energy of reactions
Enzyme active sites are complimentary to the ______ ______ of the reaction
transition state
Stronger/additional interactions with the transition state as compared to the ground state lower the ______ ______
activation barrier
Physical and thermodynamic factors contributing to ΔG‡:
1. ________________________
- ________________________
- ________________________
- ________________________
- reduction in entropy (less free motion)
- solvation shell of hydrogen-bonded water around Sand P
- distortion of substrates (like stickasedid)
- need for proper alignment of catalytic functional groups
______ _____ are the most common biochemical reactions
Proton transfers
In enzyme kinetics ____ ____ must be short so that [S] does not change much
Reaction times
___ is the substrate concentration at ½ Vmax
Km
enzyme is saturated with substrate at __
Vmax
- binding of substrate to enzyme
equilibrium is normally reached within microseconds
as [S] increases eventually the enzyme becomes saturated
- reaction and release of product
this is the slow step and limits the rate of the whole reaction
Reactions kinetics are dictated by a rapid, concentration-dependent binding of substrate to the enzyme followed by a slower generation of released product
Steady State Kinetics
Steady State Kinetics
- binding of substrate to enzyme
_____________________________
_____________________________
- reaction and release of product
_____________________________
_______ ______ are dictated by a rapid, concentration-dependent binding of substrate to the enzyme followed by a slower generation of released product
- equilibrium is normally reached within microseconds
as [S] increases eventually the enzyme becomes saturated
- this is the slow step and limits the rate of the whole reaction
Reactions kinetics
The ____-____ equation was based on a specific kinetic model but many enzymes that use different (complex) mechanisms yield a similar hyperbolic V vs [S]curve and the Vmax and Km’s determined are valuable parameters.
Michaelis-Menten
The turnover number, ___
kcat
If the rate limiting step is binding of substrate: kcat= ___
k1
If the rate limiting step is release of product: kcat = __
k3
If there are several slow steps kcat is a _______ function
complex
In all cases ____ is a first order rate constant (1/sec) and is equal to the number of substrate molecules converted to product in a given unit of time on a single enzyme molecule when the enzyme is saturated with substrate
kcat
parallel lines indicate a___-___ (double-displacement) pathway
Km for S1increases as [S2] increases
Ping-Pong
Inhibitor blocks binding of substrate
Vmaxis not affected by inhibitor, but the apparent Kmis raised
Usually inhibitor is not metabolized by the enzyme it blocks
Methanol is converted by alcohol dehydrogenase to toxic formaldehyde
Ethanol is like a competitive inhibitor (converted to acetaldehyde)
Reversible Competitive Inibition
Inhibitor interacts with ES at a site distinct from the active site and slows the reaction
Vmaxand apparent Kmare lowered by the inhibitor
Reversible Uncompetitive Inhibition
Inhibitor interacts with E or ES at a site distinct from the active site and slows the reaction
Vmaxis lowered and apparent Kmraised (shown above) or lowered by the inhibitor
Reversible Mixed Inhibition
Inhibitors that bind covalently or very strongly and destroy a required functional group are ________
Irreversible
_______ inhibitors bind to the enzyme, make it part way through the reaction mechanism then block subsequent steps
These make good drugs
Suicide
