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Energy, Enzymes,
and
Chemical Reactions
Defining Energy
 Potential energy is the
capacity to do work.
 Kinetic energy is the energy
of motion.
Chemical energy
Potential energy of molecules
Thermal (heat) energy
Energy that is not given off as kinetic
energy ; is considered “wasted energy”
Laws of Thermodynamics
 First law –Energy is not created or
destroyed only transferred between
forms.
 The total amount of energy in the
universe remains constant.
 Second law -- No energy
conversion can ever be 100%
efficient.
 Energy always flows from more
useful forms of energy to forms
that are less useful.
Endergonic reaction
 Energy is put
Energy of a reaction over time
into the reaction
40
 Uphill reaction
Energy (Joules)
35
30
25
20
Series1
15
10
5
0
1
2
3
4
5
6
Time (s)
 For example:
Glycolysis
7
8
9
Exergonic reaction
Energy is
released during
the reaction
Downhill reaction
Energy (Joules)
Energy over time in a reaction
60
40
Series1
20
0
1
2
3
4
5
6
7
Time (s)
Example: The Kreb’s
cycle and
electron transport
system
ADENOSINE TRIPHOSPHATE
--Is the cell’s energy source
Is
a nucleotide consisting of three
phosphate groups, a five-carbon
sugar (ribose), and the nitrogen
base (adenine).
Adenosine
Adenine
Ribose
3 Phosphate groups
IMPORTANCE OF ATP
Cells
transfer energy from food to
ATP
ATP delivers energy where ever
energy is needed.
movement
 chemical reactions
 growth

HOW IS ENERGY RELEASED?


When a phosphate group is removed (energy is
released when the bonds that hold the phosphate
groups together are broken).
Results –

ATP becomes ADP (Adenosine
Adenosine
Ribose
Diphosphate)
2 Phosphate groups
• ADP is changed into ATP when a phosphate
group is added.
Chemical Reactions
Indicators of chemical reactions
Release of light or heat
Formation of a gas
Formation of a precipitate
Color change
Release of odor
All chemical reactions:
Have two parts
1.Reactants - the substances you
start with
2.Products- the substances you end
up with
The reactants turn into the products.
Reactants  Products
Symbols used in equations


indicates a reversible reaction.
or
indicates the direction
in which a reaction occurred.
Reaction Energy
All chemical reactions are accompanied
by a change in energy.
Exothermic - reactions that release
energy to their surroundings (usually in
the form of heat)
Endothermic - reactions that need to
absorb heat from their surroundings to
proceed.
What is a catalyst?
 A substance that decreases the
activation energy needed to start a
chemical reaction and increases the
rate of the chemical reaction.
 Are not changed or used up during a
chemical reaction.
Enzyme Structure & Function
 Enzymes – catalysts that
speed up the rate of a
reaction.
 Equilibrium - when a reaction
is running at the same rate
forward as well as in reverse.
Four shared features
1. Enzymes don’t make anything
happen that could not happen on
its own, it just makes it happen
faster.
1. Enzymes can not be
permanently changed or used up.
3 The same type of enzyme
usually works whether the
reaction is occurring in a
forward or reverse motion
3 Each type of enzyme is very
picky
Enzyme-Substrate interactions
 Substrates attach to enzymes at the
enzyme’s active site.
 Enzymes have one or more active
sites
 Active site-A specific shape that will
only fit a specific substrate.
Active Site
 A specific shape that will only
fit a specific substrate. (Like a
lock & Key).
 When the substrate locks into
the active site, the reaction
begins with lower activation
energy because of weaker
bonds within the molecule.
Enzyme
Lock–and–Key Model
1 A substrate (reactants) attaches
to an enzyme’s active site.
2 Enzyme- Substrate Complex
The enzyme reduces the
activation energy of the reaction.
3 The enzyme is NOT changed by
the reaction. A new product is
formed.
Factors influencing enzyme activity
 Temperature
 pH
 Salinity
 Feedback Inhibition