13. Bioenergetics Flashcards
what is bioenergetics
the quantitative analysis of the capture, transformation, storage, and utilization of energy in organisms
state the first law of thermodynamics
for any physical change, the total amount of energy in the universe remains constant
state the second law of thermodynamics
the universe always tends towards disorder (entropy)
what is enthalpy
the heat content of a reacting system. It reflects the number and kinds of chemical bonds in the reactants and products
what are the units for enthalpy
Joules/mol
what variable is used for enthalpy
delta H
what is negative enthalpy
the reaction releases heat (exothermic)
what is positive enthalpy
the reaction requires heat input (endothermic)
what is entropy
the quantitative expression for the randomness/disorder in a system
what are the units for entropy
Joules/mol x Kelvin
what is variable is used for entropy
delta S
what is negative entropy
products are less disordered; loss of entropy
what is positive entropy
products are more disordered; gain of entropy
what is gibbs free energy
the amounts of energy capable of doing work
what variable is used for gibbs free energy
delta G
what is negative gibbs free energy
energy is released from the system (exergonic)
what is positive gibbs free energy
energy is gained by the system (endergonic)
what equation is used to relate G H and S
deltaG = deltaH - TdeltaS
what is the gas constant (R)
R=8.315 J/mol x K
describe the rates of a reaction at equilibrium
the forward and reverse rates are equal
describe the concentrations of reactants and products at equilibrium
the reactants and products have a specific, constant concentration
T or F: at equilibrium, there will be no further net change in the system
true
what does Keq measure
measures the ratio of products to reactants at equilibrium
describe the composition of a reacting system not at equilibrium
the composition will change until equilibrium is reached
how can we measure the magnitude of a driving force towards equilibrium for a reaction not at equilibrium
delta G
what does delta G close to zero mean
closer to zero= closer to equilibrium
what is ∆G’o
the biochemical standard free energy under the conditions of: pH 7, 1M, 25 degrees C, and 1 atm
T or F: ∆G’o is constant for each chemical reaction
true
T or F: ∆G’o and K’eq are heavily linked
true
describe the relationship between ∆G’o and K’eq when ∆G’o is negative
when it’s negative, the products have less free energy than the reactions, making the reaction spontaneous. Therefore the products are favored, so we have a large Keq
what equation connects ∆G’o and K’eq
∆G’o = -RTlnK’eq
where T is temp in Kelvin, and R is the gas constant
T or F: small changes in ∆G’o produce large changes in K’eq
true; for each tenfold change in Keq, the delta G only increases by 5.7 kJ/mol
describe the amount of standard free energy produced in hydrolysis of acid anhydrides
hydrolysis of acid anhydrides produces large decreases in standard free energy as compared to hydrolysis of other compounds
how is ∆G different from ∆G’o
∆G is the actual free energy change in GIVEN cellular conditions, not STANDARD cellular conditions
what equation links ∆G and ∆G’o
∆G=∆G’o + RTln(Q)
what is Q
known as the mass action ratio. It’s the ratio of products over reactants
why do we use Q instead of Keq
because Keq is only at equilibrium
what are the units of Q
ALWAYS M (must convert to M before plugging into the equation)
describe the relationship between ∆G and ∆G’o when: [reactant]=[product]
they’re equal
describe the relationship between ∆G and ∆G’o when: [reactant]>[product]
∆G is smaller than ∆G’o
describe the relationship between ∆G and ∆G’o when: [reactant]
∆G is larger than ∆G’o
ln(1)=
0
ln(fraction)=
negative number
ln(integer)=
positive number
what are the two different driving forces for a reaction
enthalpy and entropy
describe an enthalpy driven reaction
delta S is negative (more order produced), delta H is negative (very exothermic), then delta G is also negative
describe an entropy driven reaction
if delta H is positive (endo.) but delta S is very positive, then delta G can still be negative
T or F: in reactions near equilibrium, Q and Keq are very far apart
false; they’re near each other
describe the size of delta G absolute value when the reaction is near equilibrium
the absolute value of delta G is small
T or F: near equilibrium, free energy changes are small and the reactions are easily reversible
true
T or F: near equilibrium, the direction of the reaction can switch easily
true
T or F: at reactions far from equilibrium, Q and Keq are very close together
false; Q and Keq are very far apart
describe the size of delta G when the reaction is far from equilibrium
the delta G absolute value is very large
T or F: far from equilibrium, free energy changes are large so the reactions are not easily reversible
true
how are reactions far from equilibrium regulated
regulated by modulation of enzyme activity
describe ΔG’o in a sequential reaction
each reaction has its own characteristic standard free energy: ΔG’o1 and ΔG’o2. These are additive
T or F: the standard free energy values for a sequential reaction are additive
true
what does the additive nature of gibbs free energies in sequential reactions explain
explains how a thermodynamically unfavorable reaction (+ΔG) can be driven in the forward direction by coupling it to a highly exergonic reaction (large -ΔG) through a shared intermediate
in coupling/sequential reactions, what is often the shared intermediate
Pi or H2O
what are many cellular reactions coupled to
the highly exergonic ATP hydrolysis reaction
state the ATP hydrolysis formula
ATP + H2O = ADP + Pi + H
describe the ATP turnover rate
the turnover rate in our body is HUGE because we go through so much ATP so we need to generate a bunch as well
describe the linkage types in nucleoside triphosphates
one phosphate ester and two phosphoanhydrides
in nucleoside triphosphate, describe the phosphate ester
its formed by a linkage of the a-phosphoryl group to the 5’-oxygen of ribose
in nucleoside triphosphate, describe the two phosphoanhydrides
they’re formed by the a/B and B/y linkages between phosphoryl groups
what is the charge on ATP
very negatively charged
what is the role of Mg2+ in ATP
the positive charge stabilizes ATP by shielding some of the negative charges (either in aqueous solution or in the active site of enzymes)
list the 3 reasons large amount is energy is released during ATP hydrolysis
- electrostatic repulsion between neg charged O’s of phosphoanhydride groups is less after hydrolysis
- hydrolysis products are better solvated than ATP itself
- resonance stabilization of the product inorganic phosphate (Pi)
T or F: we can assume ∆G is actually more negative than ∆G°’
true
when talking about ATP hydrolysis, what value do we use for ∆G°’
-30.5 kJ/mol
what does it mean to have a large negative ∆G’o
there’s lots of energy being held, and when cleaved the energy is released. The products are stabilized
what is PEP
phosphoenol pyruvate
how are the products of PEP hydrolysis stabilized
there are two possible constitutional isomers
what is 1,3BPG
1,3-bisphosphoglycerate
how are the products of BPG hydrolysis stabilized
ionization and resonance
how are the products of phosphocreatine hydrolysis stabilized
resonance
how are the products of thioesters hydrolysis stabilized
resonance
what is acetyl CoA
a thioester
which molecules have their hydrolysis products stabilized by alleviation of electrostatic repulsion
ATP
which molecules have their hydrolysis products stabilized by ionization
ATP, BPG, thioesters
which molecules have their hydrolysis products stabilized by resonance
ATP, BPG, thioesters, phosphocreatine
which molecules have their hydrolysis products stabilized by isomerization
PEP
how do BPG, PEP, and phosphocreatine interact with ADP
they’re all able to phosphorylate ADP into ATP
which molecules are able to synthesize ATP
BPG, PEP, phosphocreatine
why does a lot of biochemistry involve phosphorylation
to increase the free energy of that compound so that the compound has more free energy to give up in subsequent reactions. Phosphorylation primes the compound for future catabolic reactions
why is it important that ATP have an intermediate level of delta G’o and not a super negative or small negative value?
ATP can carry energy from a high energy phosphoryl group donor produced by catabolism (ie PEP) to a low energy phosphoryl acceptor compound (ie glucose)
This converts the low energy compound into a more reactive species with better leaving groups
