Bioenergetics Flashcards
What are bioenergetics?
The study the transfer and utilization of energy in living systems
Predicts if a reaction is possible or not
What is energy?
The ability to do work or cause changes ?
How is energy measured?
Measured in joules or calories
State the first law of thermodynamics
Energy cannot be created nor destroyed only converted/transformed from one form to the next
Energy of the universe is constant
State the second law of thermodynamics
Every energy transfer or spontaneous process increases the entropy of the universe
How is the first law of thermodynamics applied to chemistry?
- metabolic reactions obey this law as they release/take heat from surroundings
- enthalpy change🔼H= change in bond energy that occurs during a chemical reaction under constant temperature and pressure
- this is also the max heat released or absorbed during a chemical reaction under constant pressure in a cell
Explain enthalpy change
- enthalpy change🔼H= change in bond energy that occurs during a chemical reaction under constant temperature and pressure
- this is also the max heat released or absorbed during a chemical reaction under constant pressure in a cell
Reactions with a negative value of 🔼H realest heat to surroundings(exothermic)
Reactions with a positive value of 🔼H, remove heat from surroundings (endothermic )
How does the second law of thermodynamics apply to chemistry?
- Entropy measures the degree of randomness (disorder).
- Cells maintain highly ordered structures and obey this law by releasing some energy as heat to the surroundings during metabolism
- heat transferred increases entropy of surroundings
Explain entropy
Entropy measures the degree of randomness(disorder)
Reactions with a negative value of 🔼S have decreased disorder
Reactions with a positive value 🔼S means increased disorder
🔼S of a reaction cannot by itself predict whether a reaction is spontaneous
What is Gibbs Free energy?
The maximum amount of useful energy that is available to do work in a cell
-Predicts the direction of a spontaneous reaction at constant temperature and pressure
Explain the Gibbs free energy formula and it’s interpretations
🔼G = 🔼H- T 🔼S
🔼G= free energy change
🔼H= enthalpy change
🔼S= entropy change
Spontaneous reactions, 🔼G is negative EXERGONIC
Non-spontaneous reactions, 🔼G is positive ENDERGONIC
Predict 🔼G when enthalpy change is negative and. Entropy is positive
When 🔼H is-ve and 🔼S is +ve the 🔼G is -ve and reaction is ALWAYS spontaneous
Predict 🔼G when enthalpy change is negative and Entropy is negative
When 🔼H and 🔼S are negative
🔼G is spontaneous at low temperatures
Predict 🔼G when both 🔼H and 🔼S are both positive
🔼G can be + or -
Spontaneous at high temperature
Predict 🔼G when enthalpy change is positive and entropy change is negative
🔼G is never spontaneous
What are 3xergonic reactions?
🔼G is negative
- Reactions proceeds spontaneously in the direction written A —> B with net release of free energy
- Proceeds toward a state of lower free energy
What is an endergonic reaction?
- 🔼G is positive
- Energy must be added to proceed in the direction written (B—> A)
- Conversion of B —> A is non-spontaneous
- Proceeds toward a state of higher free energy
Contrast exergonic and endergonic reactions
Exergonic - spontaneous, negative 🔼G, releases free energy, increases entropy of universe
Endergonic - non-spontaneous, 🔼G is positive, free energy must be added, decreases entropy of universe
What is 🔼G at equilibrium?
🔼G is zero
Describe spontaneousity achieving equilibrium
-Reactions will proceed spontaneously with a net release of free energy until equilibrium has been established
Describe spontaniety of equilibrium reactions
At equilibrium the reaction is at its lowest state of free energy and has no tendency to change
At equilibrium the free energy change is zero and the net reaction ceases
What does 🔼G depend on?
The initial concentration of reactants and products
What are the symbols in the reaction formula:
🔼G= 🔼G^o + RTln[B]/[A]
🔼G^o= the standard free energy change
R= is the gas constant
T is the absolute temperature (K)
[A] and [B] are the actual concentrations of reactants and products
What does Gibbs free energy change predict?
The direction of a reaction toward equilibrium starting at any concentration of reactants and products
What is the difference in Gibbs free energy in reversible reactions?
In reversible reactions, 🔼G for the forward reaction is equal in magnitude but opposite in sign to the reverse reaction
What is standard free energy change (🔼G^o)?
The free energy change of a reaction under standard conditions when initial reactant and product concentrations are 1M
Standard conditions are _____ concentrations, ______K (______degrees Celsius) and ______ atm
1
298
25
1
What is 🔼G’?
The value of 🔼G^o at pH=7.0, [H2O]= 55M
Why can’t 🔼G^o predict the direction of physiological reactions?
Cannot predict the direction of a reaction under physiological conditions because it is not altered by concentrations of substrates and reactants
🔼G is composed solely of…
The constants R, T and K eq
🔼G^o= -RTlnKeq
What are the chemical conditions of standard Gibbs free energy ?
- under standard conditions
- [B]= [A]= 1M
- 🔼G^o is positive
- Reaction is non spontaneous in the written direction A —> B
- formation of A is favoured
What are conditions of standard free energy and equilibrium?
- Reaction is allowed to establish equilibrium
- At equilibrium more A than B I.e. K eq< 1
- Equilibrium lies to the left
- formation of reactants (A) was favoured
Describe standard free energy change and reaction direction if Keq is above 1
🔼G^o is negative and reaction is forward A —> B
Describe the standard free and direction of the reaction when Keq is below 1
🔼G^o’ is positive
Reverse reaction B—> A
Describe the standard free energy change and direction of the reaction when Keq=1
Reaction at equilibrium
🔼G^o’ =0
How can a reaction with 🔼G^o - 0 proceed spontaneously in the cell?
Under non-standard conditions
-Non-spontaneous reaction made spontaneous by altering concentrations of reactants and products
Apply Le Chatelier’s principle
-[B]<B (forward)
🔼G is negative
What is the additive property of 🔼G and 🔼G^o’
🔼G and 🔼G^o’ of consecutive reactions are additive
- This additive property of free energy changes is very important in biochemical pathways
- As long as the sum of the 🔼Gs is negative, the pathway can proceed as written.
Glucose +ATP —> glucose 6-p + ADP 🔼G^o’= -4kcal/mol
Glucose-6-p —> fructose 6-p 🔼G^o’= +0.4 kcal/mol
Net: glucose-6-p +ATP —> fructose 6-p + ADP 🔼G^o’=-3.6 kcal/mol
What is thermodynamic coupling?
The free energy released by exergonic reactions is used to drive endergonic (unfavorable) processes in the cell
Coupling occurs through common intermediates which can transfer chemical energy between the two reactions
A+B —> C +D
D +X —> Y + Z
- 🔼G^o’ values for the coupled reactions are additive
- The overall process is exergonic with a 🔼G^o’< 0(-ve)
Coupling favorable reactions with an unfavorable reaction might…
Yield an overall favorable reaction
Where is the energy stores in ATP?
In the high energy phosphoanhydride bonds
What is the 🔼G^o’ of ATP hydrolysis?
🔼G^o’= -7.3 kcal/mol
ATP+H2O —> adp+p
What is the 🔼G^o’of ADP hydrolysis?
🔼G^o’= 7.3 kcal/mol
ADP+ H2O—> AMP + P
Why is ATP hydrolysis exergonic?
Hydrolysis of ATP is exergonic because ADP
and P are more stable with less free energy than ATP
Why is ATP unstable?
Instability and high bond energy of the phospho-anhydride bond of ATP arises from repulsion between the negatively charged phosphate groups
Also the free phosphate anion is more stable than it is in ATP due to an increase in resonance and solubility(increased entropy)
Energy released as heat cannot be _______ into energy ________ processes such as biosynthetic reactions or maintenance of ion gradients
Transferred
Requiring
Energy transfer is facilitated by….
Transferring the phosphate group to a reactant or protein generating a common intermediate that is part of the energy requiring process
What are high energy compounds?
Compounds with a free energy of hydrolysis equal to or higher than ATP
Are mainly phosphate or thioester compounds
What is the phosphorylation transfer potential?
🔼G^o’ if hydrolysis
Compounds with higher 🔼G^o’ of hydrolysis than AaTP can…
Be used to make ATP
ATP can be used to form compounds with…
Lower 🔼G^o’ of hydrolysis
The high energy bonds of UTP, CTP and GTP are…
Equivalent to ATP and are synthesized from ATP by nucleoside phosphokinases
Give some examples of substrate phosphorylation
- Succinate thiokinase in TCA cycle
- PFK-1, Glucokinase, Pyruvate kinase, phospoglycerate kinase in glycolysis
What is substrate level phosphorylation?
An enzyme catalyzed reaction where a phosphate group is transferred from a compound with a higher phosphoryl group potential to another compound having a lower phosphoryl group potential
Catalyzed by kinases
What is a low energy state for a cell?
Cells with a low [ATP]/[ADP] ratio is said to be in a low energy state
What is a high energy state for a cell?
Cells with a high [ATP]/ [ADP] is said to be in a high energy state
The free energy change of ATP hydrolysis depends greatly om…
The concentrations of ATP, ADP and P
Describe ATP and energy balance in the cell
In the cell the ATP hydrolysis reaction is kept far from equilibrium by maintaining the [ATP] higher [ADP]
Cells maintain ATP homeostasis using the [ATP]/ [ADP] ratio as a signal to regulate the rate of ATP generation to match its utilization
What processes might use energy utilization?
Muscle contraction
Active transport
Biosynthesis
Detoxification
Thermogenesis
