Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
38 Cards in this Set
- Front
- Back
standard state conditions
|
all reactants/products at 1 M
temp = 25 C P = 1 atm |
|
ΔG°
|
delta g naught
delta G under STD conditions |
|
ΔG'°
|
standard biological gibbs free energy change
T= 25 P= 1 atm all products/reactants at 1M EXCEPT [H+][H2O][Mg++] |
|
what concentrations deviate from ΔG° in ΔG'° and what are the values?
|
[H+] = 10^-7 M (pH = 7)
[H2O] = 55.5 M (conc. of water in 1 L) [Mg++] = 1mM |
|
ΔG
|
gibbs free energy change for rxn that takes place under some defined set of conditions that are not biological or "standard"
|
|
R=
|
8.315 J/mol K
|
|
equation for ΔG'°
|
ΔG'° = -RT ln Keq where ln = 2.3 log base 10
|
|
ΔG in terms of ΔG'°
|
ΔG = ΔG'° + (RT x ln [prod]/[react])
|
|
what does "coupled" reaction mean?
|
product of one reaction is consumed in other reaction
|
|
Keq > 1 means...
|
spontaneous under STD, exergonic
|
|
Keq < 1 means...
|
not spontaneous under STD, endergonic
|
|
how to affect spontaneity
|
change prod/react ratio
|
|
Keq of 2 coupled rxns =
|
Keq of first rxn times Keq of second rxn
|
|
how to tell if coupled reaction is spontaneous or not?
|
find Keq of A<--->C
plug in to ΔG'° equation and see if it is positive or negative |
|
another way besides Keq to solve for ΔG'° of coupled rxn
|
calculate ΔG'° for A-->B
calculate ΔG'° for B-->C add the two together |
|
what is the purpose of coupling rxns?
|
a thermodynamically unfavored rxn can be made more favorable by coupling it to a second, more exergonic, rxn
|
|
how does a coupled reaction make an unfavorable rxn more favorable? (2)
|
1) the [prod]/[react] ratio of endergonic rxn can be decreased by coupling to the exergonic rxn (exergonic rxn will use up the product)
2) the free energy released in the exergonic rxn (often splitting of ATP) can be used to drive the "activation" of the reactant in the endergonic rxn |
|
why is splitting of ATP so exergonic?
|
ATP is very unstable, so splitting it to ADP (more stable) is favorable and releases a lot of energy
|
|
detailed view of glutamine synthesis (how the coupled rxn works on the molecular lvl) (4 steps)
|
1) glutamate- stable, low energy, unreactive + ATP- very unstable, very high energy
2) phosphate gets cleaved from ATP to create ADP. phosphate group attaches to glutamate to form glutamyl phosphate, a less stable compound, more reactive, higher energy 3) glutamyl phosphate is able to react with an amine group (NH3) causing the loss of the phosphate 4) net effect is 1 glutamine and 1 Pi (plus the ADP that left earlier) |
|
ways that compounds can be activated by reaction with ATP
|
basically depends where the compound breaks the phosphate
1) RO: (those are electrons) can react with one phosphate of ATP to make R-phosphate + ADP 2) R-pyrophsophate (2 P groups) + AMP 3) R-adenylate (attaches to phosphate + nucleotide) + PPi (pyrophosphate) |
|
so what is the coupling of ATP actually doing for compounds?
|
the high energy makes ATP breaking off phosphates very favorable so compounds that normally wouldn't be reactive, can react with ATP. this forms an intermediate that is more reactive than it's original form, allowing it to proceed forward.
|
|
why is the hydrolysis of ATP exergonic?
|
products ADP + P are much more stable than the reactant ATP (ΔG = Gprod - Greact)
|
|
why is ATP unstable?
|
electrostatic repulsion of the 3 phosphate groups
|
|
in biological systems, many thermodynamically unfavorable rxns are...
|
made favorable by coupling to ATP hydrolysis (or energetic equivalent)
|
|
what drives ATP hydrolysis in the forward direction? (2)
|
mass action due to...
1) high [reactant]: the 55.5 M concentrations of water is super huge 2) low product: [H+] is low because of pH |
|
why is ADP + Pi more stable than ATP in water? (3)
|
1) less electrostatic repulsion
2) more H-bonding between H2O and products 3) Pi by itself has a greater variety of resonance states than in ATP |
|
why does ADP lose it's proton (from phosphate group) in physiological pH? (what??)
|
[H+] is relatively low at physiological pH so the weakly acidic Pi and ADP (pKa ~slightly lower than physiological pH) are driven towards deprotonation
|
|
equation of ATP hydrolysis
|
H2O + ATP --> ADP + Pi + H+
|
|
if ATP hydrolysis is so energetically favorable, how can ATP persist in aqueous solutions?
|
because it has high activation energy (WHAT??) which can be lowered with the appropriate enzyme (ATPase)
|
|
what do you call bonds that are high energy and contain a phosphate?
|
high phosphate transfer potential bond
|
|
other kinds of high energy bonds
|
1) enol phosphate
2) acyl phosphate 3) acyl thioester 4) pyrophosphate |
|
acyl
|
R-C=O (other bond of C can bind to whatever)
|
|
enol
|
alkene (double bond) with OH group attached to one of the carbons on the double bond
|
|
are all bonds that have phosphates high energy? give example
|
no. phosphate + primary
OH only has ~13.8 kj/mol |
|
energy of enol phosphate bond
|
-61.9 kj/mol
|
|
energy of acyl phosphate bond
|
-41.8 kj/mol
|
|
energy of acyl thioester bond
|
-31.4 kj/mol
|
|
energy of pyrophosphate bond
|
-30.5 kj/mol
|