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MCAT

Unit 2: Lesson 1

Foundation 1: Biomolecules

The thermodynamics of ATP hydrolysis in living cells

Problem

The free energy start text, G, end text of a biochemical system quantifies the capacity of the system to do mechanical work. start text, G, end text changes over the course of a chemical reaction. The change in start text, G, end text during a reaction at the biochemical standard state is written delta, start text, G, end text, ’, degrees and is proportional to the standard transformed equilibrium constant start text, K, end text, ’, start subscript, start text, e, q, end text, end subscript, according to the following equation:
delta, start text, G, end text, ’, degrees, equals, minus, start text, R, T, space, end text, l, n, start text, space, K, end text, ’, start subscript, start text, e, q, end text, end subscript
ATP hydrolysis represents one of the main biochemical mechanisms through which the free energy acquired during catabolic cellular metabolism is liberated to power cellular activities.
start text, A, T, P, end text, start superscript, 4, minus, end superscript, plus, start text, H, end text, start subscript, 2, end subscript, start text, O, end text, right arrow, start text, A, D, P, end text, start superscript, 3, minus, end superscript, plus, start text, P, end text, start subscript, start text, i, end text, end subscript, start superscript, 2, minus, end superscript, plus, start text, H, end text, start superscript, plus, end superscript
delta, start text, G, end text, ’, degrees, equals, minus, 30, point, 5, start fraction, start text, k, J, end text, divided by, start text, m, o, l, end text, end fraction
The actual change in free energy for ATP hydrolysis, symbolized by delta, start text, G, end text, varies according to cell type and prevailing physiological conditions. For example, table 1 reports variation in delta, start text, G, end text values for various rat cell types under normal physiological conditions, along with cellular ATP and ADP concentrations.
Table 1. delta, start text, G, end text of ATP hydrolysis, ATP concentration ([ATP]), and ADP concentration ([ADP]) for three different rat cell types under normal physiological conditions.
[ATP][ADP]delta, start text, G, end text of ATP hydrolysis
Hepatocyte3, point, 38, start text, m, M, end text1, point, 32, start text, m, M, end textminus, 34, point, 9, start fraction, start text, k, J, end text, divided by, start text, m, o, l, end text, end fraction
Myocyte8, point, 05, start text, m, M, end text0, point, 93, start text, m, M, end textminus, 41, point, 2, start fraction, start text, k, J, end text, divided by, start text, m, o, l, end text, end fraction
Neuron2, point, 59, start text, m, M, end text0, point, 73, start text, m, M, end textminus, 37, point, 7, start fraction, start text, k, J, end text, divided by, start text, m, o, l, end text, end fraction
Lymphocyte2, point, 62, start text, m, M, end text0, point, 70, start text, m, M, end text?
Which of the following does not represent a possible explanation for the large negative delta, start text, G, end text, ’, degrees for ATP hydrolysis?
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