Topic 2 Enzymology Essential
Chapter 5 The Working Cell
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
2012 Pearson Education, Inc.
Lecture
edited
by Harttini
N.
Lecture
by Edward
J. Zalisko
Learning outcome
1. Explain how energy is transformed during life
processes
2. Explain how a chemical reaction can either
release energy or store energy
3. Describe ATP and explain why it is considered to
be the energy currency of a cell
4. Define enzyme and explain how enzymes cause
a chemical reaction to speed up
5. Discuss the specificity of enzymes
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ENERGY AND THE CELL
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5.11 Chemical reactions either release or store
energy
___________________is a chemical reaction that
release energy.
These reactions release energy in covalent bonds of the
reactants.
Burning wood releases energy in glucose as heat and
light.
Cellular respiration releases energy slowly and uses
some of the released energy to produce ATP.
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Potential energy of molecules
Reactants
Amount of
energy
released
Energy
Products
Exergonic reaction, energy released
5.11 Chemical reactions either release or store
energy
An ______________________ requires an input of energy
and yields products rich in potential energy.
Endergonic reactions
begin with reactant molecules that contain relatively little potential
energy
end with products that contain more chemical energy.
Eg. photosynthesis that produced energy-rich sugar molecules
from energy in sunlight.
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Potential energy of molecules
Products
Energy
Reactants
Endergonic reaction, energy required
Amount of
energy
required
5.11 Chemical reactions either release or store
energy
A living organism carries out thousands of
endergonic and exergonic chemical reactions.
The total of an organisms chemical reactions =
___________________.
A _________________a series of chemical
reactions that either
builds a complex molecule
breaks down a complex molecule into simpler
compounds.
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5.11 Chemical reactions either release or store
energy
_______________ uses energy released from
exergonic reactions to drive endergonic reactions
usually using the energy stored in ATP molecules.
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5.12 ATP drives cellular work by coupling
exergonic and endergonic reactions
______, adenosine triphosphate consists of
nitrogenous base adenine
five-carbon sugar ribose
three phosphate groups
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5.12 ATP drives cellular work by coupling
exergonic and endergonic reactions
Hydrolysis of ATP releases energy by transferring
its third phosphate from ATP to some other
molecule in a process called _________________.
Most cellular work depends on ATP energizing
molecules by phosphorylating them.
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ATP:
Adenosine Triphosphate
Phosphate
group
P
Adenine
Ribose
Hydrolysis
P
ADP:
H2O
Hydrolysis of ATP
releases energy by
transferring its third
phosphate from ATP to
other molecule in
phosphorylation
Energy
Adenosine DiphosphateThe structure and hydrolysis of ATP
5.12 ATP drives cellular work by coupling
exergonic and endergonic reactions
3 main types of cellular work driven by ATP:
1. chemical
2. mechanical
3. transport
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Chemical work
Mechanical work
Transport work
ATP
ATP
ATP
Solute
P
Motor
protein
P
P
Reactants
Membrane protein
P
P
P
Product
Molecule formed
ADP
Protein filament moved
ADP
P
How ATP powers cellular work
Solute transported
ADP
5.12 ATP drives cellular work by coupling
exergonic and endergonic reactions
ATP is a renewable source of energy for the cell.
In the ATP cycle, energy released in an exergonic
reaction, such as the breakdown of glucose,is used
in an endergonic reaction to generate ATP.
ATP
Energy from
exergonic
reactions
ADP P
The ATP cycle
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Energy for
endergonic
reactions
Gp. Disc.: ATP
ATP can be broken down or synthesized
Does AMP ADP require or release energy? *Why?
Is ADP ATP an exergonic or endergonic reaction? *Why?
Which can be
represented by the
graph:
ADP ATP?
OR
ADP AMP?
Which can be
represented by the
graph:
ADP ATP?
OR
ADP AMP?
E.g., Glycolysis
Is energy is used up
or released when a
phosphate group is
removed from a
molecule?
ADP ATP: energy
is used up or
released?
Glycolysis (Later)
Is energy is used up or
released when ATP is
broken down to ADP?
Is energy is used up or
released to transfer
phosphate to glucose?
HOW ENZYMES FUNCTION
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5.13 Enzymes speed up the cells chemical
reactions by lowering energy barriers
Although biological molecules possess much potential
energy, it is not released spontaneously.
An energy barrier must be overcome before a chemical reaction
can begin.
This energy is called ________________________.
Reactant
Enzyme
Energy
Energy
Activation
energy barrier
Reactant
Products
Without enzyme
The effect of an enzyme in lowering EA
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Activation
energy
barrier
reduced by
enzyme
Products
With enzyme
5.13 Enzymes speed up the cells chemical
reactions by lowering energy barriers
Enzymes
function as biological catalysts by lowering the EA
needed for a reaction to begin
increase the rate of a reaction without being consumed
by the reaction
are usually proteins, although some RNA molecules can
function as enzymes
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Animation: How Enzymes Work
Right click on animation / Click play
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The graph illustrate the course of a reaction with and without an enzyme.
1. Which curve represents the enzyme-catalyzed reaction?
2. What energy changes are represented by the lines a, b and c?
Energy
a
b
Reactants
Products
Progress of the reaction
5.14 A specific enzyme catalyzes each cellular
reaction
An enzyme
is very selective in the reaction it catalyzes
has a shape that determines the enzymes specificity.
The specific reactant that an enzyme acts on is
called the enzymes ____________.
A substrate fits into a region of the enzyme called
the ______________.
Enzymes are specific because their active site fits
only specific substrate molecules.
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Enzyme available
with empty active
site
Active site
1. Sucrase starts with an
empty active site
Enzyme
(sucrase)
The catalytic cycle of an enzyme
Enzyme available
with empty active
site
Active site
Substrate
(sucrose)
2
Substrate binds
to enzyme with
induced fit
Enzyme
(sucrase)
2. Sucrose enters the active site.
The active site changes shape
slightly to embrace substrate
more snugly (induced fit)
The catalytic cycle of an enzyme
Enzyme available
with empty active
site
Active site
Substrate
(sucrose)
2
Substrate binds
to enzyme with
induced fit
Enzyme
(sucrase)
3. The strained bonds react
with water, and the substrate
is converted to products
H2O
Substrate is
converted to
products
The catalytic cycle of an enzyme
4. The enzyme
releases the
products and
emerges
unchanged
Enzyme available
with empty active
site
Active site
Substrate
(sucrose)
2
Glucose
Substrate binds
to enzyme with
induced fit
Enzyme
(sucrase)
Fructose
H2O
4
Products are
released
3
Substrate is
converted to
products
5.14 A specific enzyme catalyzes each cellular
reaction
For every enzyme, there are optimal conditions
under which it is most effective.
Temperature affects molecular motion.
An enzymes optimal temperature produces the highest
rate of contact between reactants and enzymes active
site.
Most human enzymes work best at 3540C.
Optimal pH for most enzymes is near neutrality.
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Temperature
Increasing temperature causes molecules to ___________________
Weak bonds break first: H-bonds, hydrophobic interactions
Stronger bond break later: ionic bonds
Structure and surface configurations (including active site) are altered
Enzyme losses its catalytic functions
Enzyme is said to be denatured
When the structure of the enzyme is fully destroyed, no catalysis
takes place
1. Every enzyme has an optimum temperature that usually
reflects the environment where the enzyme is naturally
found
2. Reaction rate is highest at the optimal temperature
pH
Changes in pH changes the concentration of _______in the medium
As [H+] changes, charges on the R groups change
This causes the ____________between charged R groups to break
as the charges are _____________________
The 3-dimensional structure is then destroyed
The enzyme loses all catalytic activities and is completely denatured.
Every enzyme has an optimum pH that usually reflects the
environment where the enzyme is naturally found
Maximum rate
Maximum rate of
of reaction
reaction pepsin
trypsin
Rate of reaction
trypsin
pepsin
Optimum pH
(pepsin)
4
pH
Optimum pH
(trypsin)
10
c.
b.
a.
d.
f.
e.
You should now be able to
1. Explain how energy is transformed during life
processes
2. Explain how a chemical reaction can either
release energy or store energy
3. Describe ATP and explain why it is considered to
be the energy currency of a cell
4. Define enzyme and explain how enzymes cause
a chemical reaction to speed up
5. Discuss the specificity of enzymes
2012 Pearson Education, Inc.
