Metabolism and energetics basics Flashcards
at what pH is ATP chemically stable
6-9
hydrolysis of ATP
ATP -> ADP + Pi
ATP -> AMP + PPi
which hydrolysis of ATP releases most energy and when does this occur
ATP -> AMP + PPi
energy crisis signal of cells; intense exercise
Why is ATP hydrolysis so energetically favourable
- relieves electrostatic repulsion between the phosphate groups
- increased entropy; ΔS becomes more positive
- released phosphate ions are hydrated
- high energy bonds of the phosphate group
what is the ΔG of ATP hydrolysis
-31 to -50 kJ/mole
what is the group carrried in high-energy linkage of ATP
Phosphate
what is the group carried in high-energy linkage of NADH, NADPH and FADH2
electrons and hydrogens
what is the group carrie din high-energy linkage of Acetyl CoA
Acetyl group
what is the group carried in high-energy linkage of carboxylated biotin
carboxyl group
what is the group carried in high-energy linkage of S-adenosylmethionine
methyl group
what is the group carried in high-energy linkage of uridine diphosphate glucose
glucose
3 stages of catabolsim of sugars, FA and AA
- glycolysis, beta-oxidation and transamination
- TCA cycle
- oxidative phosphorylation
first law of thermodynamics
energy cannot be created or destroyed, but can be tranformed from one form to another
thermodynamics =
study of energy transfer
types of energy
chemical, potential, mechanical, heat etc
another name for chemical bond energy
Enthalpy
symbol for enthalpy
H
energy when bonds are made =
energy is released
stronger the bond, more energy released
energy when bonds are broken
energy is required
stronger the bond, more energy neeeded
bond energy =
energy required or released during bond breaking and making
energy change of a reaction
ΔH
the sum of energy used when bonds are broken during a reaction and released during the formation of the new bonds
ENTHALPY CHANGE
negative ΔH
when heat is lost from the molecle and released to the surroundings = exothermic
postive ΔH
when heat is taken up from the surroundings = endothermic
which ΔH reactions are more likely to occur
negative ΔH aka exothermic
do negative ΔH reactions occur
yes they are most likely to occur
do postive ΔH reactions occur
althugh less likely, some reactions with positive ΔH will occur becuase of the 2nd law of thermodynamics - ENTROPY
2nd law of thermodynamics
all processes must increase the entropy of the universe
symbol for entropy
S
what is entropy
S - level of disorder or nuber ways something can be arranged. All living things sturggles against the tendencay to disorder
= increased entropy
what reactions are favourble in terms of entropy
reactions where entropy increases; positve ΔS
symbol for gibbs free energy change
ΔG
what is ΔG
Gibbs free energy change
purpose of gibbs free energy change
to determine whether a reaction can occur or not, considering both entropy and enthalpy.
equation for gibbs free energy change
ΔG = ΔH - TΔS
units of ΔG
kJ/mol
in terms of ΔG, when will a reaction occur spontaneously
when ΔG is negative aka exergonic reaction
in terms of ΔG, when will a reactin NOT occur spontaneously
when ΔG is postive aka endergonic
what is an endergonic reaction
when ΔG is postive - will not occur spontaneously
what is an exergonic reaction
when ΔG is negative - will occur sponatneousl y
is ΔG a fixed value for a reaction?
No -it will change as the reaction proceeds towards equilibrium
when is ΔG zero
at equilibrium
what is ΔG at equilibrium
zero
unit for temperature in ΔG
kelvin
conversion of degrees C to Kelvin
+ 273
25 degrees C = 298 K
what is 25 degrees C in kelvin
298K
what is standard free energy change
ΔG°’
- when concentration of all reactants and products is 1M
- temperature is 25C/298K
- pH = 7 (biological systems)
what is ΔG°’ like for reversible reactions compared to irreversibe reactions
ΔG°’ is much smaller (less negative) in reversible reactions, and so dependign on condtitions, the reaction can go either way.
Irreversible reactions have more negative ΔG°’ and so only one direction is energetically favourable, regardless of condtions
Example of reversible reaction
G6P F6P
G6P -> F6P
In standard conditions, ΔG°’ +1.7kJ/mol and so forward reaction will not spontaneously occur
BUT
In cell condtions, ΔG°’ -2.5kJ/mol and so forward reaction occurs spontaneously
equation for relating ΔG to ΔG°’
ΔG = ΔG°’ + RT ln [AB] / [A][B]
R = gas constant 8.314
T in kelvin
ln = natural log
relating ΔG°’ to equilbrium constant
ΔG°’= - RT lnKa
ΔG = ΔG°’ + RT ln [AB] / [A][B]
at equilbirum, ΔG = 0
ΔG°’ = - RT ln [AB] / [A][B]
KA = [AB] / [A][B]
therefore ΔG°’= - RT lnKA
equilibrium constatn
KA = [AB]/[A][B]
How can energetially unfavourable reactions occur
by coupling them to favourable reactions
example of energetically unfavourable reaction that occurs by coupling
Glutamate + NH4+ -> glutamine + H20, ΔG°’ = +15kJ/mol
ATP + H2O -> ADP + Pi + H+ = -30kJ/mol
Glutamate + NH4+ + ATP -> glutamine + ADP + Pi
ΔG°’ = + 15 + (-30) = -15kJ/mol = favourable
oxidising agent
substance that recieves electrons
reduction =
gain of electrons
reducing agent =
substance donating electrons
E°
redox potential
what is E°
the abilty of a carrier to donate electros to another electron acceptor molecule
symbol for redox potential
E°
where do electrons flow
from a carrier with a negative E° to a carrier with a more postive E°
what are E° relative to
2H+ + 2e- ⇄ H2 which is set at 0.00V
what is the movement of elctrons in relation to 2H+ + 2e- ⇄ H2 if the redox pair has a negative E°
electrons move from the reduced substanct (Mg) to the H+
what is the movement of elctrons in relation to 2H+ + 2e- ⇄ H2 if the redox pair has a positve E°
electrons move from the H2 to the oxidised substance (Mg2+)
half reactions
- half reaction with higher E° will act as the reduction reaction
- half reaction with the lower E° will act as the oxidation reaction
which half reaction will be the oxidation reaction
with lower E°
which half reaction will be the reduction reaction
with higher E°
ΔE°’ =
reduction potention of reduction reaction - reduction potential of oxidation reaction
what is a spontaenous reaction in terms of ΔE°’
ΔE°’ is postive
spontaneous reactions occur downhill to create products containing less free energy than the reactants
condtions of ΔG°’ and ΔE°’ for a spontaneous reaction
ΔG°’ = negative ΔE°’ = positive
releating ΔG°’ to redox potentials
ΔG°’ = -n F ΔE°’
n = number of electrons transferred F = faraday constant, 96485 J/V/mol
