BIOL 103 Lecture Notes - Lecture 23: Santa Barbara City College, Adenosine Triphosphate, Exergonic Reaction
Attia
Santa Barbara City College
Biol 103
Cell Biology
● Coupling reactions
○ ATP – adenosine triphosphate
■ Used for the capture, transfer and storage of energy
■ ATP ADP + Pi is exergonic
● The energy of the P-O bond in ATP is much higher than the O-H
bond in the ADP that forms following hydrolysis
● Phosphate groups are negatively charged and repel each other.
Therefore, the formation of ATP requires energy to overcome this
repulsion and form a covalent bond between phosphate groups.
Breaking this bond releases a lot of energy
■ ATP can also transfer energy by donating a phosphate group
(phosphorylating)
○ dG values are additive when coupling reactions
● As a reaction proceeds, the concentration of the reactants and the products change. This
affects the dG
○ In general, most reactions are reversible. The direction in which reactions proceed
is dictated by the concentration of the reactants and the products. For a reaction A
B, adding more A speeds up the forward reaction
○ At equilibrium dG = 0 and the forward rate = the reverse rate
● **dG predicts the spontaneity, not the RATE of reaction. AND the rate of reaction does
not affect the equilibrium
● For an exergonic reaction to proceed, an energy barrier, the activation energy, must be
overcome and this explains the slow speed of the reaction
● Enzymes are biological catalysts. They increase the rate of reaction by decreasing the
activation energy
○ Kinase: an enzyme that transfers a phosphate group from a donor to an acceptor
○ Phosphatase: an enzyme that removes a phosphate group
○ Phosphorylase: an enzyme that catalyzes the addition of a phosphate group from
an inorganic phosphate
○ Mechanism of action:
■ Enzymes bind the substrates of the reaction at their active site
■ Catalysis takes place at the active site and is mediated by
● Orienting substrates in the proper conformation to facilitate the
interaction
● Inducing strain in the substrates and facilitate reaction
● Temporarily adding chemical groups to substrates
■ Some enzymes require other molecules to function, termed cofactors
■ At low concentrations of the substrate, the addition of an enzyme increases
the rate of the reaction significantly
Document Summary
Used for the capture, transfer and storage of energy. Atp adp + pi is exergonic. The energy of the p-o bond in atp is much higher than the o-h bond in the adp that forms following hydrolysis. Phosphate groups are negatively charged and repel each other. Therefore, the formation of atp requires energy to overcome this repulsion and form a covalent bond between phosphate groups. Breaking this bond releases a lot of energy. Atp can also transfer energy by donating a phosphate group (phosphorylating) Dg values are additive when coupling reactions. As a reaction proceeds, the concentration of the reactants and the products change. The direction in which reactions proceed is dictated by the concentration of the reactants and the products. B, adding more a speeds up the forward reaction. At equilibrium dg = 0 and the forward rate = the reverse rate. **dg predicts the spontaneity, not the rate of reaction.
