From last class From last class… ΔG = ΔH – TΔS  The reactions of metabolism are

enzyme catalyzed and all reversible.

If the ΔG is negative then the forward reaction is spontaneous and the reverse reaction needs a free energy input.

If the ΔG is positive then the forward reaction needs a free energy input and the reverse reaction is spontaneous.

When an equilibrium is reached between the forward and reverse reactions the ΔG is 0 and the cell is dead!

Cells prevent this by undergoing a series of reactions in a chain, so that the products of one reaction are the reactants in another and therefore cannot go in reverse.

ATP ATP is the primary source of free

energy in cells.

Notice in the diagram of ATP that it is a nucleic acid composed of adenine (nitrogenous base), ribose (pentose) and three phosphate groups (P groups).

  The reaction that creates the

free energy for the cell is the removal of the terminal phosphate group from ATP by ATPase forming ADP and an inorganic phosphate group. This reaction produces 31 KJ/mol of free energy in a lab setting. In a living cell the amount of free energy is closer to 54 KJ/mol.

ATP ADP + P Cycle

ATP ADP + P Cycle The breaking of ATP into ADP

+ P is an exergonic process since ATP is not as stable as the products.

The cell uses the energy to drive endergonic processes.

  The free energy released by the

removal of the terminal phosphate is not given off as heat or else the cell would die. Instead it is immediately coupled with an endergonic reaction which uses the energy in the P-bond. The attachment of the phosphate group is called phosphorylation.

  An example of this process is in

active transport, ATP’s phosphate group is removed and then phosphorylated to protein carriers, changing their shape and letting ions into or out of the cell against the concentration gradient.

Oxidation-Reduction Reactions (Redox)

Oxidation: A process in which an atom loses one or more electrons.

Reduction: A process in which an atom gains one or more electrons.

  Redox Reactions: A reaction in

which one atom transfers an electron/electrons to another atom. Oxidation and reduction both occur.

  Oxidizing Agent: The substance

that gains an electron; so called because it forces another atom to become oxidized.

  Reducing Agent: The substance

that loses an electron; so called because it forces another atom to become reduced.

Very Easy to see in Ionic reactions

Very Easy to see in Ionic reactions

More difficult in covalent interactions

The atoms being oxidized and reduced are harder to determine when dealing with covalently bonded molecules.

In these reactions, the unequal sharing of electrons in a polar bond is thus considered to be a loss or a gain of electrons.

Redox with Covalent moleculesEasiest to see in

combustion reactions:

CH4 (g) + 2O2 (g) CO2 + 2H2O + Energy (on the board)

Mr. Jarrell ROCKS!!!