Thermodynamics of Metabolism Flashcards

1
Q

What must be true for reactions to be easily reversed by changing the ratio of products to reactants?

A

The reaction must be a near-equilibrium reaction

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2
Q

What will happen when the concentration of reactants in a reaction is greater than the equilibrium concentration of reactants?

A

The reaction will move in the forward direction until equilibrium is attained.

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3
Q

What are the rates of near-equilibrium reactions regulated by?

A

The relative concentration of reactants to products

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4
Q

What types of reactions are most metabolic reactions?

A

Near-equilibrium reactions

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5
Q

What is the implication for highly exergonic metabolic reaction (delta G is much less than 0)?

A

The reaction is irreversible and goes to completion.

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6
Q

What effect does a highly exergonic reaction have on a pathway that it is a part of?

A

Confers directionality on the pathway (makes the entire pathway irreversible).

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7
Q

What does every metabolic pathway have that commits a pathway to completion?

A

A committed step (usually near the beginning of the pathway

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8
Q

What is required for the reverse reaction of a highly exergonic pathway?

A

A different pathway for at least one of the reaction steps (or the existence of independent interconversion routes).

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9
Q

What does the existence of independent interconversion routes for a forward reaction and its reverse reaction allow?

A

Independent control of the two processes

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10
Q

What type of control would be impossible without independent interconversion routes for a forward reaction pathway and its reverse reaction pathway?

A

Being able to shut off one reaction while turning on the other, depending on whether product or reactant is required.

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11
Q

What remains constant in a pathway?

A

The concentration of metabolites

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12
Q

What step in a reaction determines flux (the rate of flow)?

A

The RDS (the slowest step or steps)

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13
Q

What is true of the RDS of a reaction pathway?

A

Its delta G is negative and large, so it operates far from equilibrium.

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14
Q

Why is the delta G of the RDS large and negative?

A

Because the RDS is slow, its product is used in the next reaction before it can equilibrate back to the reactants of the previous step.

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15
Q

What is true of all near-equilibrium reactions that are downstream from an RDS?

A

They all have the same flux

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16
Q

How can flux control points be identified in practice?

A

They have a large delta G and are relatively insensitive to concentration variations

17
Q

What do reaction steps with large negative delta G permit?

A

The establishment of steady flux for a pathway.

18
Q

What are four mechanisms that cells use to control flux through rate determining steps?

A

1) Allosteric control
2) Covalent modification
3) Substrate cycles
4) Genetic control

19
Q

What type of flux control mechanism controls the concentration of enzyme through protein biosynthesis?

A

Genetic control

20
Q

What type of flux control mechanism works by phosphorylating/dephosphorylating specific enzyme sites?

A

Covalent modification

21
Q

What type of flux control mechanism can increase flux by increasing the forward reaction and slowing the reverse?

A

Substrate cycles (reactions catalyzed by two different enzymes, one forward and one reverse)

22
Q

Which is more sensitive to allosteric effectors, single, unopposed non-equilibrium reactions or substrate cycles (reactions whose forward and reverse reactions are catalyzed by different enzymes)?

A

Substrate cycles

23
Q

Which control mechanism for flux involves use of substrate, products, co-enzymes, or negative feedback?

A

Allosteric control