Transcript Redox Reactions and ATP

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 molecules
 Easiest to see in
combustion reactions:
Mr. Jarrell ROCKS!!!
 CH4 (g) + 2O2 (g)  CO2
+ 2H2O + Energy (on the
board)