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39 Cards in this Set

  • Front
  • Back
What does one call the reaction when the free energy and equilibrium constants are close to zero?
near-equilibrium reaction
Where do most enzymes in a metabolic pathway act?
At equilibrium
Which reactions, when considering enzymes, are irreversible?
exergonic rxns
Living organisms are thermodynamically open or closed living systems?
What sets the flux rate in a pathway?
rate-determining step
What are two major qualities of the rate-determining step?
1. functions far from equilibrium
2. has a large negative free energy change
attatchment of a phosphoryl group
Substrate cyle
two opposing metabolic reactions that function together to hydrolyze ATP, but provide a control point for regulating metabolic flux
Can an equilibrium process perform useful work? (G=0)
What do reactions that function near equilibrium respond rapidly to?
Changes in substrate concentration
What do a series of near-equilibrium reactions downstream from the rate-determining step have in common?
same flux
Allosteric control
enzymes controlled by effectors that can be substrates, products or coenzymes of the pathway
Name four ways cells control metabolic flux.
-Allosteric control
-Covalent Modification
-Substrate cycles
-Genetic control
What type of acid is palmitate?
fatty acid
Why does oxidative metabolism proceed in a stepwise fashion?
So the released free energy can be recovered in a manageable form at each exergonic step
"high energy intermediates"
packets of energy that undergo exergonic breakdown to drive endergonic processes
What are some forms of energy currency that the cell uses?
-phosphorylated compounds like nucleotide ATP
-compounds containing thioester bonds
-reduced coenzymes like NADH
Does ATP occur in all lifeforms?
From what does ATP get its biological importance?
the large free energy change that accompanies cleavage of its phosphoanhydride bonds
What are the two things that can be transferred when these bonds break?
-phosphoryl group transferred leaving behind ADP
-nucleotidyl (AMP) group is transferred leaving pyrophosphate
Phosphoryl group-transfer potentials
measure of the tendency of phosphorylated compounds to transfer their phosphoryl groups to water
Does a favorable free energy change indicate how fast the rxn occurs?
Are ATP and other phosphorylated compounds kinetically stable?
How large does the negative value for free energy have to be for something to be considered high energy?
greater than -25 kJ/mol
Bond energy
energy required to break a covalent bond
What factors are responsible for the "high energy" character of phosphoanhydride bonds like those in ATP?
-resonance stabilization of a phosphoanhydride bond is less than that of its hydrolysis products
- (most important) destabilization effect of the electrostatic repulsions between the charged groups of a phosphoanhydride compared to those of its hydrolysis products
-phosphoanhydride has a smaller solvation energy when compared to those of its hydrolysis products
What is the initial step in the metabolism of glucose?
conversion to glucose-6-phosphate
Hexokinase catalyzes theh formation of what?
glucose-6-phosphate (catalyzes the transfer of a phosphoryl group from ATP directly to glucose)
ATP hydrolysis
phosphoryl group transfer is directly to water
What does it mean when one says ATP hydrolysis is thermodynamically favored but kinetically disfavored? (explain example from book)
the reaction of glucose with ATP that yields glucose-6-phosphate: the activation energy for the nonenzymatic transfer of a phosphoryl group from ATP to glucose is greater than that for ATP hydrolysis, so without hexokinase, the hydrolysis reaciton predominates
ATP breaking down to ADP and Pi
orthophosphate cleavage
ATP breaking down to AMP and PPi
phyrophosphate cleavage
Inorganic pyrophosphatase
cleaves PPi into 2Pi
What drives the pyrophosphate cleavage in the synthesis of an aminoacyl-tRNA to completion?
irreversible hydrolysis of PPi
Through what does ATP drive endergonic reactions?
through exergonic process of phosphoryl group transfer and phosphoanhydride hydrolysis
What is one way ATP can be regenerated?
by coupling its formation to a more highly exergonic metabolic process
Substrate-level phosphorylation
ATP can be formed from ADP by direct transfer of a phosphoryl group from a "high-energy" compound
Oxidative phosphorylation
when ATP is generated indirectly using the energy supplied by transmembrane proton concentration gradients
(in oxidative metabolism)

- called photophosphorylation in photosyntheseis
catalyze the flow of energy from "high-energy" phosphate compounds to ATP and from ATP to "low-energy" phosphate compounds

(the kinases actually transfer the phosphoryl groups