Chapter 8

Objectives
○ Distinguish between the following pairs or terms:
catabolic and anabolic pathways; kinetic and
potential energy; open and closed systems;
exergonic and endergonic reactions
○ Explain how the nature of energy transformations is
guided by the two laws of thermodynamics
○ Describe how ATP functions as the universal energy
shuttle in cells
○ Describe the structure of enzyme-substrate
interactions and how enzymes catalyze biological
reactions
Introduction
Characteristics of organisms are all the
end-products of the chemical reactions
that occur in their cells
 The cell is a mini factory

 Roughly 8.64 x 1026 reactions per day
 Chemical reactions carried out for the
purpose of energy transformation or making
necessary substances
Energy-The Capacity to do Work
Energy is described and measured by how it
affects matter
 Two types of energy:

 kinetic-energy of motion
 potential-stored energy because of structure or location
 Example: the energy stored in chemical bonds
Why we are open systems
Laws of Energy Conservation
Thermodynamics = study of energy
transformations
Two laws govern energy transformation:

 First law (energy conservation)
○ total amount of energy in universe is constant
 can be transferred or transformed but cannot
be created or destroyed
 Second law (entropy-disorder- increases)
○ every energy transformation increases entropy
 energy available for doing useful work
decreases with every transformation
Organization of the Chemistry of
Life into Metabolic Pathways

Metabolism transforms matter and energy
 Subject to the laws of thermodynamics
○ Metabolism is the sum of an organism’s
chemical reactions

Metabolic pathway has many steps that
begin with a specific molecule and end
with a product
 Each step catalyzed by a specific enzyme
Catabolic vs. Anabolic

Catabolic: break down complex
molecules into simpler compounds
 Releases energy

Anabolic: build complicated molecules
from simpler ones
 Consumes energy
G = Gibbs Free Energy
(Delta) G = Free energy available to do work in
a cell
 A - G means a rxn gives off energy; it provides
power

A + G means a rxn needs energy; it will not run
unless energy is first added
 Every rxn has a specific G

Energy Relationships in Living Things

Chemical reactions in cells either store or release
energy
 endergonic reactions require input of energy
○ energy input equals difference in potential
energy between reactants and products
exergonic reactions release energy
○ energy released equals difference in potential
energy between reactants and products
 cellular metabolism is sum total of all endergonic and
exergonic reactions in cells
Energy Relationships

ATP is cell’s energy shuttle
 most cell reactions require small amounts of
energy
 food storage molecules contain large
amounts of energy
 energy in food molecules converted to
energy in ATP
○ one food molecule=many ATP (e.g. 1 x
glucose=36 ATP)
Energy Relationships

Hydrolysis of ATP releases energy
 Most energy is located in the covalent bond between
2nd and 3rd phosphate groups
 easily hydrolyzed
 forms ADP and phosphate group
 ATP ADP + Pi ( means PO4 = phosphate)
ATP synthesis
endergonic reactions of cellular respiration
phosphorylate ADP-reforms ATP
 ADP + Pi (PO4 = phosphate) ATP
 More about this in Chapter 9

Enzymes

Enzymes are large protein molecules that act
as biological catalysts

Energy of activation (EA) is “energy barrier”,
amount of energy needed to start a reaction

Enzymes can lower energy barriers = EA

Enzymes cannot lower G!
Enzyme Process

Specific enzymes
catalyze each cell
reaction
 reactant=substrate
 reactant binds to
enzyme active site
 substrate converted
to product
 enzyme unchanged
and releases product
Enzymes and Denaturation

Factors that affect enzyme activity




temperature
pH
salt concentration ( ions)
presence of co-factors
denaturation
 Denaturation = disruption of the
enzyme structure due to adverse
conditions
 Example: PH to high or low
 These factors may lead to
Question: How do you stop enzyme activity but not
destroy the enzyme? Answer: Inhibition
 Inhibitors block enzyme action,
○ competitive inhibitors-bind to active
site
○ noncompetitive inhibitors-bind to
second site on enzyme
○ negative feedback-inhibition by
product of reaction
 some pesticides and antibiotics
function by inhibiting enzymes
 Inhibitors most often work on a
temporary basis
 BUT>>>>>>>
A+BC : G= - 8.6 kcal needs 8.6
kcal to run the reaction
A.
B.
True
False
Checklist









What is energy?
What are the types of energy?
What are the laws of thermodynamics?
Catabolic vs anabolic?
What is ∆G?
+ ∆G means what? - ∆G means what?
What do these look like graphed?
What are enzymes? What do they do?
Do enzymes change the ∆G?