Active transport in the opposite direction is non spontaneous It requires

Active transport in the opposite direction is non

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Active transport in the opposite direction is non- spontaneous. It requires energy input. Entropy influences whether a reaction will occur spontaneously -- membrane example
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Entropy influences whether a reaction will occur spontaneously -- molecule example bigger molecule -more order -less stable smaller molecules -less order -more stable e n e r g y r e l e a s e i n c r e a s e d e n t r o p y G: Gibb’s free energy: = a measure of potential energy = a measure of instability & order = a measure of ability to do work = a measure of tendency to change to a stable state Lots of free energy means you have lots of energy to use for work
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In spontaneous reactions, free energy is reduced G = free energy, S = entropy Big molecule Smaller molecule Starting state hydrolysis Ending state G 1 = H 1 – TS 1 G 2 = H 2 – TS 2 Bigger ordered molecule Less ordered molecule H=stored energy (high) H stored energy is low S=entropy (low) S entropy is high T=temperature (constant) T the same The change in G = the change in H –T(the change in S) Δ G = ΔH –T ( ΔS) Math result: Δ G is a negative number in spontaneous reactions (i.e. reactions in which H decreases and S increases ). At state 2, H (stored energy) is small, S (entropy) is large. Small H – Large S yields a negative number. Change in free energy - Δ G loss of free energy, exergonic reaction (spontaneous, gives off energy) + Δ G gain of free energy, endergonic reaction (requires energy input)
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One more time High H (stored energy) Low S (entropy) Less stable Greater work capacity More potential energy Low H (stored energy) Greater S (entropy) More stable Less work capacity Less potential energy - ΔG An exergonic (spontaneous, energy yielding) reaction Kid Diffusion gradient Molecule
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Energy for cellular work. ATP = Adenosine Triphosphate Adenosine is the same nucleoside found in RNA (the sugar has an OH in the second position) Juxtaposed negatively charged O’s cause very unstable bonds , lots of G (Free Energy). Analogy: A compressed spring ready go—unstable and powerful
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Hydrolysis of ATP is exergonic. The spring is sprung. When a P group is released by ATP, its energy is exerted on the molecule that receives the P group (usually by changing the receiving molecule’s shape). Thus, the receiving molecule ( the phosphorylated molecule ) is energized. Δ G = -7.3 kcal/mole (in vitro) Note the hydrolysis of ATP has a negative Δ G value, meaning a loss of free energy. This is the sign of an exergonic reaction
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ATP’s energy is not lost during a reaction. The released phosphate group is attached to another molecule. ATP’s energy is transferred to the molecule that receives it. The receiving molecule is said to be PHOSPHORYLATED (it now has a P group added to it). The receiving molecule is now energized and reactive. Linkage (joining) of the reactants (Glu & NH 3 ) is thus facilitated There is plenty of free energy from ATP to push the reaction Endergonic Exergonic Exergonic ATP energizing a reaction To build glutamine from glutamic acid and NH3 requires 3.4 kcal/mol of energy input. ATP provides 7.3 kcal/mole of energy to help the reaction
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ATP is recycled ATP is made from ADP (adenosine diphosphate) by: 1. Energy from the sun via photosynthesis 2. Or from energy released during the exergonic breakdown (catabolism) of sugar during respiration ATP is then used to phosphorylate molecules and make them more reactive.
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