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
