Biochem Exam 3- Carbohydrate Metabolism

Front 1

standard state conditions

Back 1

all reactants/products at 1 M
temp = 25 C
P = 1 atm

Front 2

ΔG°

Back 2

delta g naught
delta G under STD conditions

Front 3

ΔG'°

Back 3

standard biological gibbs free energy change
T= 25 P= 1 atm
all products/reactants at 1M
EXCEPT
[H+][H2O][Mg++]

Front 4

what concentrations deviate from ΔG° in ΔG'° and what are the values?

Back 4

[H+] = 10^-7 M (pH = 7)
[H2O] = 55.5 M (conc. of water in 1 L)
[Mg++] = 1mM

Front 5

ΔG

Back 5

gibbs free energy change for rxn that takes place under some defined set of conditions that are not biological or "standard"

Front 6

R=

Back 6

8.315 J/mol K

Front 7

equation for ΔG'°

Back 7

ΔG'° = -RT ln Keq where ln = 2.3 log base 10

Front 8

ΔG in terms of ΔG'°

Back 8

ΔG = ΔG'° + (RT x ln [prod]/[react])

Front 9

what does "coupled" reaction mean?

Back 9

product of one reaction is consumed in other reaction

Front 10

Keq > 1 means...

Back 10

spontaneous under STD, exergonic

Front 11

Keq < 1 means...

Back 11

not spontaneous under STD, endergonic

Front 12

how to affect spontaneity

Back 12

change prod/react ratio

Front 13

Keq of 2 coupled rxns =

Back 13

Keq of first rxn times Keq of second rxn

Front 14

how to tell if coupled reaction is spontaneous or not?

Back 14

find Keq of A<--->C
plug in to ΔG'° equation and see if it is positive or negative

Front 15

another way besides Keq to solve for ΔG'° of coupled rxn

Back 15

calculate ΔG'° for A-->B
calculate ΔG'° for B-->C
add the two together

Front 16

what is the purpose of coupling rxns?

Back 16

a thermodynamically unfavored rxn can be made more favorable by coupling it to a second, more exergonic, rxn

Front 17

how does a coupled reaction make an unfavorable rxn more favorable? (2)

Back 17

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

Front 18

why is splitting of ATP so exergonic?

Back 18

ATP is very unstable, so splitting it to ADP (more stable) is favorable and releases a lot of energy

Front 19

detailed view of glutamine synthesis (how the coupled rxn works on the molecular lvl) (4 steps)

Back 19

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)

Front 20

ways that compounds can be activated by reaction with ATP

Back 20

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)

Front 21

so what is the coupling of ATP actually doing for compounds?

Back 21

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.

Front 22

why is the hydrolysis of ATP exergonic?

Back 22

products ADP + P are much more stable than the reactant ATP (ΔG = Gprod - Greact)

Front 23

why is ATP unstable?

Back 23

electrostatic repulsion of the 3 phosphate groups

Front 24

in biological systems, many thermodynamically unfavorable rxns are...

Back 24

made favorable by coupling to ATP hydrolysis (or energetic equivalent)

Front 25

what drives ATP hydrolysis in the forward direction? (2)

Back 25

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

Front 26

why is ADP + Pi more stable than ATP in water? (3)

Back 26

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

Front 27

why does ADP lose it's proton (from phosphate group) in physiological pH? (what??)

Back 27

[H+] is relatively low at physiological pH so the weakly acidic Pi and ADP (pKa ~slightly lower than physiological pH) are driven towards deprotonation

Front 28

equation of ATP hydrolysis

Back 28

H2O + ATP --> ADP + Pi + H+

Front 29

if ATP hydrolysis is so energetically favorable, how can ATP persist in aqueous solutions?

Back 29

because it has high activation energy (WHAT??) which can be lowered with the appropriate enzyme (ATPase)

Front 30

what do you call bonds that are high energy and contain a phosphate?

Back 30

high phosphate transfer potential bond

Front 31

other kinds of high energy bonds

Back 31

1) enol phosphate
2) acyl phosphate
3) acyl thioester
4) pyrophosphate

Front 32

acyl

Back 32

R-C=O (other bond of C can bind to whatever)

Front 33

enol

Back 33

alkene (double bond) with OH group attached to one of the carbons on the double bond

Front 34

are all bonds that have phosphates high energy? give example

Back 34

no. phosphate + primary
OH only has ~13.8 kj/mol

Front 35

energy of enol phosphate bond

Back 35

-61.9 kj/mol

Front 36

energy of acyl phosphate bond

Back 36

-41.8 kj/mol

Front 37

energy of acyl thioester bond

Back 37

-31.4 kj/mol

Front 38

energy of pyrophosphate bond

Back 38

-30.5 kj/mol