Theme 2 – Topic B Review – Metabolism
Why is ATP considered the energy currency of the cell?
* high potential energy because it posses what is called high-energy phosphate bonds.
* Bonds are unstable (easy to break)
* Much of the potential energy of ATP is associated with the arrangement of the three phosphate groups.
* Bonds - Negative charges strongly repel each other, making them unstable
* Removal of one or two of the three phosphate groups is a spontaneous reaction that releases large amounts of energy.
* ATP HYDROLYSIS is the break down of ATP to ADP and inorganic phosphate Pi.
* ATP Hydrolysis is exergonic so it releases energy and is spontaneous
How is the energy of ATP used to drive Metabolic reactions?
If you dissolve ATP in water in a test tube, the hydrolysis reaction simply releases free energy that simply warms the water.
Within a cell, energy coupling occurs. ATP is brought in close contact with a reactant molecule involved in an endergonic reaction and when ATP is hydrolyzed, the terminal phosphate group is transferred to the reactant molecule. (phosphorylated).
An enzyme is required to bring ATP and reactant molecule into close association.
Exergonic Catabolic pathways give us ATP (e.g. cellular respiration)
Exergonic reaction hydrolyzes ATP. This energy is then used to drive endergonic anabolic pathways in the cell.
It cycles back. Syntehsis of ADP and Pi is an energy-requiring endergonic process that requies energy of exergonic break down of complex molecules that contain free energy (glucose, proteins, etc.).
How do enzymes lower the activation energy required for reactions to take place?
Activation Energy – initial energy investment required to start a reaction
Transition State – molecules that gain the necessary EA occupy this state where bonds are unstable and are ready to be broken
Catalyst – chemical agent that speeds up the rate of a reaction without itself...