10. Bioenergetics Flashcards
photosynthetic autotrophs
use the energy of sunlight to convert low -G (energy) and H2O into energy-rich complex sugar molecules
photosynthesis equation and notes
6 CO2 + 6H2O –> (CH2O)6 + 6O2
the reaction has a large positive ΔH and large negative ΔS (the products have more enthalpy and are more ordered than the reactants)
heterotrophs
extract the chemical potential energy stored in sugars and other organic compounds to release CO2 and H2o
equation for glycolysis and notes
(CH2O)6 + 6 O2 –> 6CO2 + 6H2O
-reaction has a large negative ΔH and large positive ΔS (the products have lost energy and are less ordered)
-the G is released slowly in many steps using several metabolic pathways
equation for ΔG?
ΔG = -RTln(Keq)
(T= temp in K, R = 8.31 J/molK)
what is the formula for ΔG°? what does it mean?
ΔG° = -RTln(Keq)
-under “standard” conditions (25° C, 55 M H2O, [reactant] = 1M)
what does ΔG’° mean?
correcting the pH to pH=7
if K’eq = 19 at 25°C, then ΔG’°= -(8.315)(298)(ln19) = -7296 J/mol
what does it mean if K’eq if positive? negative? =1?
Negative: ΔG’° is negative, spontaneous rxn
positive: ΔG’° is positive, non-spontaneous
=1: ΔG’° is 0, rxn at equilibrium
what does it mean if ΔG’° is negative? positive?
negative: the products contain much less energy than the reactants (spontaneous)
positive: the products contain more energy than the reactants (non-spontaneous)
what is the equation for the actual ΔG under non standard conditions?
ΔG - ΔG’° + RTln([C][D]/[A][B]
notes on bioenergetics
- both ΔG and ΔG’° are theoretical maxima. some G is always lost as heat
- even if ΔG’° is positive, the reaction can go forward if ΔG is negative
- ΔG’s of sequential reactions are additive because ΔG is path-independent (used to drive the next reaction; overall negative even if some steps are positive)
what is the common intermediate between catabolism and anabolism?
ATP (product of one, used to drive the other)
what is the equation for synthesis/hydrolysis of ATP
ATP + H2O —> ADP + Pi
explain how the synthesis of ATP can be a spontaneous reaction
-the synthesis of ATP is highly endergonic (non-spontaneous)
-however, it is coupled with ATP hydrolysis, which is highly exergonic (spontanous)
-the OVERALL reaction is exergonic, allowing ATP synthesis to occur spontaneously
-this is a very common method used in bioenergetics
explain relief of charge repulsion in ATP hydrolysis
one molecule with four negative charges is converted into two molecules with two negative charges each
-this reduces the charge repulsion, which is partly why ATP hydrolysis is so exergonic (relieves repulsion)
this is done by:
1. hydrolosis of a phosphate group from ATP (to make ADP)
2. deproponating the phosphate group to create resonance (e- distributed evenly throughout the oxygen atoms)
explain how there is an entropy increase due to ATP hydrolysis
there are more resonance forms of ADP + Pi than of ATP, which creates an entropy increase
(products are more stable than reactants; more ways to order itself)
solvation
the process of solvent molecules surrounding solute particles
explain the hydrolysis of 1,3 bis-phosphoglycerate, and say what it is used for
used in glycolysis and photosynthesis
-a phosphate is removes to alleviate charge, just like in ATP hydrolysis
equation:
1,3 bis-phosphoglycerate + H2O –> 3-phosphoglycerate + Pi
-overall reaction is exergonic
explain the hydrolysis of phosphoenolpyruvate into pyruvate
removes a phosphate to alleviate charge and form a more stable molecule (just like in ATP hydrolysis)
-phosphoenolpyruvate is a VERY energetically rich molecule, meaning the energy released can be used to synthesize ATP
explain how ATP is used to convert Glu + NH3 into Gln (endergonic process)
- the phosphate from ATP is transferred to an enzyme (or a substrate) which becomes activated
-ex: the energy of Glu is raised by phosphorylation
(hydrolysis of ATP provides energy to convert Glu into Gln) - the reaction is completed by displacement of the Pi by NH3+, which is an exergonic reaction
(replaces the phosphate with an amino group)
if ATP has so much energy, then why does it not spontaneously decompose?
although the reaction is spontaneous, it is very slow because it has a HIGH ACTIVATION ENERGY
-therefore, enzymes are used to lower the activation energy and allow the release of energy
PPi
inorganic pyrophosphate
-it is the product of hydrolyzing TWO phosphates off of ATP (AMP leftover)
-can then hydrolyze PPi to create two inorganic molecules (releases even more energy)
thioester bonds
-has a SULFUR attached instead of ozygen
used as another type of energy storage
-thioesters are less stable than oxygen esters, and therefore release more energy when broken
explain how Acetyl-CoA is used to drive reactions
-has a high-energy thioester bond which can be broken in order to drive endergonic reactions
-breaking the bond releases energy and creates more stability in the product
what is the equation of Zn in the solution? Cu?
Zn –> Zn 2+ + 2e-
Cu 2+ + 2e- –> Cu
maltate dehydrogenase
an enzyme that removes electrons from L-Maltate to produce oxaloacetate and reduce NAD+ to NADH
-maltate is dehydrogenated and oxidized (loses two e- in the form of 2H)
-NAD+ accepts H - and becomes reduced
-this releases a proton
how to find the overall redox reaction between two molecules?
- find both of their redox reactions, and find which one has the higher E’° value
- flip the reaction of the species with the more negative E’° (the one that is giving up its e-)
- cancel out intermediates to find the overall reaction
- add together the E’° values to find the overall value
note: can also flip the sign of the E’° value of the oxidation rxn then add the values
how can ΔG be calculates from redox reactions?
from the difference in emf
equation:
ΔG’° = -nFΔE’°
(F= faraday constant = 96.48 kJ/volt*mol)
