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TOPIC 7
Learning Objectives
THE WORKING CELL
After studying this topic you should be able to:
 Define the terms energy, kinetic energy, the
principle of conservation of energy, and
potential energy.
 Explain how ATP drives work in chemical
reactions in cells.
 Define the terms metabolism, enzyme,
activation energy, substrate, and active site.
 Explain how enzymes are able to speed up
chemical reactions.
 CEB Textbook Chapter 5, pages 74-82
Mastering Biology, Chapter 5
Metabolism
 The total of all the
chemical reactions in an
organism.
Adenosine triphosphate
ATP AND METABOLISM
Chemical Reactions in the
body produce and use
energy
Can you think of any?
Types of Energy
Energy
 What is energy?
- The capacity to perform work, or to move matter
in a direction it would not move if left alone.
Energy makes things happen!
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LAW OF CONSERVATION
Kinetic
OF ENERGY
Light
Energy can not be created
Heat
or destroyed, converted
from one form into another
Sound
Magnetic
Electrical
Nuclear
What types
Elastic
of energy are
used in our
Gravitational Potential
bodies?
Chemical Potential
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Potential Energy
Potential Energy
 Any form of stored energy is called
potential energy
What does ‘potential’
mean?
 Potential means an ability
to do something that
hasn’t been used yet.
 Potential energy means the
ability to release energy.
 Stored chemical energy is
called…
 Chemical potential energy
 There are two other forms of
potential energy…
Potential Energy
 All living things get
their energy from food.
Food has a store of
energy called chemical
potential energy.
 Fuels like coal, charcoal,
gas, oil, diesel
and petrol also have
stores of chemical
potential
energy.
Gravitational potential
energy (GPE)
 Gravitational
potential energy is
energy an object has
because it is high up.
 It only releases this
energy when it falls
down.
 What kind of energy
has it transferred to?
Elastic potential energy
(EPE)
 This is stored in elastic materials such as rubber,
metal springs and elastic.
How does our body transfer
energy?
ATP
Adenosine
Triphosphate
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ATP is a molecule made in the
Mitochondria of cells
ATP and Metabolism
 About 40kg of ATP is
made in cells in the
mitochondria every
day and used almost
immediately.
 You may make up to
0.5kg a minute
 At any one time you
probably have only
about 5g in your
body.
 ALL living cells make ATP
 It is the energy currency
of the cell.
 ATP is made almost
continuously and
probably lasts for less
than a minute before it is
broken down again.
ATP and metabolism
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Chemical Structure of ATP
ATP consists of:
The sugar ribose
The adenine
And three phosphate groups
 It is very similar to the
nucleotide of a nucleic acid
Structure of ATP - Simplified
How does ATP store energy?
ATP
ADP
+ Pi
When covalent bond is broken the chemical
potential energy stored in the bond is
released as a different type of energy e.g.
KINETIC
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The Covalent Bonds in ATP Store
Chemical Potential Energy
ALittle
Little
littlebit
bit
Energy
bit
Energy
of
Energy
A LOT
of
Energy
Formation of ATP
 http://www.biologyinmotion.com/atp/index.htm
l
Say that again?
ATP and metabolism
 When a cell needs energy it hydrolyses ATP
 This produces ADP and inorganic phosphate.
 In extreme circumstances ADP can be hydrolysed to
AMP
ATP in action - Active
Transport
 http://www.brookscole.com/chemistry_d/te
mplates/student_resources/shared_resources
/animations/ion_pump/ionpump.html
ATP and metabolism
 ATP is an “energy
currency” because
like money it is
constantly “recycled”
 Carbohydrates and
fats act as energy
stores (banks), while
ATP is energy
currency (money).
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ATP and metabolism
 Advantage of ATP is it
produces energy in small
‘packets’.
 A single molecule of ATP may
be enough to supply the
energy needs of a single
chemical reaction.
 ATP is constantly been used
and recycled by every living
cell.
 ATP is used in ACTIVE
TRANSPORT
Now that we have
examined a molecule
which is used to
transfer energy in
chemical reactions, lets
look at a molecule used
to reduce energy needed
for chemical reactions
to occur
Timeline of enzyme discovery
Enzymes – Biological
Catalysts
 Define the terms
metabolism, enzyme,
activation energy,
substrate, and active
site.
 Explain how enzymes
are able to speed up
chemical reactions.
1835:
Breakdown of starch to sugar by malt
1877:
Name enzyme coined to describe chemicals in yeast that ferment sugars
1897:
Eduard Buchner extracted enzyme from yeast and showed it could work outside cells
1905:
Otto Rohm exyracted pancreatic proteases to supply enzymes for tanning
1926:
James B Sumner produced first pure crystalline enzyme (urease)
and showed enzymes were proteins
1930-1936:
Protein nature of enzymes finally established when digestive enzymes
crystallised by John H Northrop
1946: Sumner finally awarded Nobel prize
What is an Enzyme?
Enzymes are specifically shaped
globular proteins, which speed
up/catalyse chemical reactions.
They are produced from glandular
tissue, which is found all over the
body.
Properties of enzymes
 All are proteins
 All are highly specific
 All are re-usable
CATALYST = a chemical agent
that changes the rate of a
reaction without being consumed
by the reaction
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Enzymes are named with the suffix “ase”
Enzyme that helps degrade cellulose (cellulase)
Enzyme that catalyses the breakdown of sugar
(sucrase).
Enzyme that makes ATP (ATP synthase)
Enzyme that makes DNA from nucleotides
(DNA polymerase).
Enzyme that turns lactose into sugar (lactase).
Enzymes in Reactions
 Normally, chemical
reactions in your body
are so slow that the cell
would die, if they were
not sped up.
 Enzymes can increase
rate by a factor of
between 108 to 1026
 An enzyme reacts on a
substrate. For
example, pepsin acts on
proteins and urease acts
on urea.
What do they look like?
Reverse transcriptase (HIV)
Naming enzymes:
 Intracellular enzymes
Work inside cells eg.DNA polymerase
 Extracellular enzymes
Secreted by cells and work outside cells eg.
pepsin, amylase
 Recommended names
Short name, often ending in ‘ase’ eg.
creatine kinase
 Systematic name
Describes the type of reaction being
catalysed eg.
ATP:creatine phosphotransferase
 Classification number
Eg. 2.7.3.2
Lock and Key?
 The ‘lock and key’ model of
enzyme operation supposes
that each enzyme has an
active site, which is
determined by its shape.
 If this shape is changed
(denatured), the enzyme
will not work.
 The active site is where all
the enzyme activity takes
place and this is specific to a
particular substrate.
More enzyme structure
DNA topoisomerase II (yeast)
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Lock and Key??
Enzymes are Proteins with a
Specific Shape
 It is thought to work like a lock and key does.
 Each key will only work on a unique lock.
Its about shape
Lock & Key model
Two molecules are bonded together at the active site and leave as
something different.
 Two molecules of a
specific shape, bind to the
active site of the enzyme.
 In doing this, bonds
between the molecules
form and a new molecule
is created, which leaves
the enzyme.
 The enzyme is now free to
join two more molecules.
E
Active site
Dehydration
Anabolic Reaction
Enzymes form an enzyme/substrate complex
Lock & Key model
Substrate + Enzyme
P1
E
E
S
E
P2
S
Enzyme/substrate complex
Enzyme/product complex
Active site
Product + Enzyme
Dehydration
Anabolic Reaction
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Lock & Key model
Lock & Key model
One molecule binds to the active site and leaves
as something different.
P1
E
E
S
S
E
E
P2
Active site
Active site
Hydrolysis
Catabolic Reaction
Hydrolysis
Catabolic Reaction
Enzyme co-factors
In anabolic reactions enzymes
bring the substrate molecules
together.
Some enzymes need co-factors to work.
Carboxypeptidase with Zinc
Glucose oxidase with FAD
In catabolic reactions the
enzyme active site affects the
bonds in substrates so they are
easier to break
Co-factors and how they work
Without the co-factor the enzyme cannot function.
Co-factors and how they work
Without the co-factor the enzyme cannot function.
E
E
Active site
Active site
After the co-factor has bound to the active site, the enzyme
can work as before.
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Co-factors and how they work
Induced fit model
a variation on the lock & key model
The enzyme changes shape, so that it can accommodate the
substrate, which can fit into the active site as a result.
E
E
Without the co-factor, the active site cannot join the
substances together. Add the co-factor and the substances
can be joined.
Induced fit model
a variation on the lock & key model
The enzyme changes shape, so that it can accommodate the
substrate.
Once this is complete, the enzyme returns to its original shape.
Activity vs inhibitors
Inhibitors = small molecules or ions that
bind to an enzyme and inhibit its
activity
•Nature's way to control and regulate
enzyme activity in biological systems
•Many drugs are enzyme inhibitors:
•e.g. HIV produces an enzyme
called protease which is required for
the activation of other viral proteins
The substrate can fit into the active site with the new shape
of the enzyme. The enzyme works on the substrate in this
form and once this is complete, it returns to the original shape.
HIV protease &
inhibitor (red)
•Protease inhibitor is a potent drug
against AIDS
Two types of enzyme inhibitor
Competitive
Non-competitive
Inhibitor binds to
active site
Prevents enzyme from reacting
with substrate
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Inhibitor binds to
active site
Inhibitor is beaten
to the active site
because there are
more substrate
particles
Prevents enzyme from reacting
with substrate permanently
by bonding with the enzyme.
A summary of inhibitors
• If binds at the active site: competitive inhibitor
• If binds elsewhere: non-competitive inhibitor
Inhibitor binds to the
enzyme and changes
the shape of the active site,
rendering it in-operable.
Enzymes lower activation energy by forming
an enzyme/substrate complex
Substrate + Enzyme
Enzyme/substrate complex
What is the deal?
ENZYME ACTIVITY
Enzyme/product complex
Product + Enzyme
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Characteristics of enzymes
 Rate of enzyme action is dependent on number of substrate
Enzymes are proteins which catalyse
reactions
molecules present
Enzymes lower Ea, the activation energy of
the reaction
Rate of Reaction (M)
Vmax = maximum rate of reaction
Vmax approached as all
active sites become filled
Some active sites free at
lower substrate
concentrations
Substrate concentration
Enzymes lower the activation energy of a reaction
Energy levels of molecules
What does enzyme activity depend on?
Initial energy state
of substrates
Activation energy
of enzyme catalysed
reaction
Activation energy
of uncatalysed
reactions
Final energy state of
products
1.
2.
3.
4.
5.
pH
Temperature
Presence of co-factors
Presence of inhibitors
Enzyme regulation
Progress of reaction (time)
Environmental conditions
are important for enzyme function
You can change the reaction
conditions like pH and
temperature. This can be
difficult for a cell which
operates under very close
tolerances. Generally, over
evolutionary time, the
enzymes are optimized to the
specific conditions.
Environmental conditions
•Proteins (and enzymes, too) are sensitive to their
chemical environment.
•Increasing temperature gives the molecules more
kinetic energy so they bump into each other more often.
•At a point, a protein will denature (lose its structure) if
too much heat is applied. Weak bonds in the enzyme will
be broken by the heat.
Cells do have several kinds of
organelles that serve as
highly environmentally tuned
compartments to perform
chemical reactions
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Enzymes denature at 60oC
Activity vs temperature
• low temperature  low kinetic energy
 substrates and enzymes less likely to
"bump" into each other and react.
Optimum temperature
Rate of reaction
• high temperature  too much kinetic
energy  enzymes "jiggle" too much
and become denatured (permanently lost
activity)
Enzyme denaturing and
losing catalytic abilities
Rate doubles
every 10oC
• most enzymes function best/optimally
at 37°C in our body
• Enzymes from different organism have
different optimal temperature (depends
on the habitat)
Temperature
Some thermophilic bacteria have enzymes with optimum
temperatures of 85oC
Denaturation
Enzymes
If a protein denatures it no longer has a
specific shape and can no longer fit the
substrate and catalyse the reaction
Enzymes work best in certain conditions:
Enzymes are
denatured
beyond 40OC
Enzyme
activity
400C
pH affects the formation of hydrogen bonds and
sulphur bridges in proteins and so affects shape.
trypsin
cholinesterase
Rate of Reaction (M)
pepsin
2
4
6
pH
8
Temp
Could be
pepsin/protease
(found in the
stomach)
Could be amylase
(found in the
intestine)
pH
pH
Changing the pH can change how well the chemical
mechanism works.
Trypsin is an enzyme that cleaves peptide bonds. It is an
intestinal digestive enzyme that works best in alkaline
conditions – too acidic it denatures.
Pepsin is an enzyme that cleaves peptide bonds. It
works well in the low pH conditions inside the stomach –
too alkali it denatures.
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Enzymes in medicine
Limitations of enzymes
Glucose oxidase + peroxidase + blue dye on dipsticks to detect
glucose in urine:
 All are denatured by heat
Glucose
Glucose oxidase
 They are affected by some
poisons (inhibitors)
Hydrogen peroxide
 They are affected by pH
peroxidase
 Some only function in the
presence of co-factors or
co-enzymes.
Dye: Blue---Green---Brown
Dye changes according to
amount of glucose
Enzyme-linked immunosorbent assays (ELISAs) detect
antibodies to infections.
Summary - Characteristics of Enzymes
1) Enzymes are CATALYSTS meaning they only change the rate of
reaction (not any of the reactants or products, they don’t get
used up either!).
Define the following terms:
1.
Anabolic reactions:
Reactions that build up molecules
2.
Catabolic reactions:
Reactions that break down molecules
3.
Metabolism:
Combination of anabolic and catabolic
reactions
4.
Catalyst:
A substance that speeds up reactions without
changing the produced substances
5.
Metabolic pathway:
Sequence of enzyme controlled reactions
6.
Specificity:
Only able to catalyse specific reactions
7.
Substrate:
The molecule(s) the enzyme works on
8.
Product:
Molecule(s) produced by enzymes
2) Each enzyme has an ACTIVE SITE
3) Enzymes are very SPECIFIC
4) Enzymes are RECYCLED. They are present in only very SMALL
AMOUNTS due to high molecular activity:
e.g. Turnover number = number of substrate molecules
transformed per minute by one enzyme molecule
Catalase turnover number = 6 x106/min
Characterictics of Enzymes Video
http://www.youtube.com/watch?v=XTUm-75-PL4
Key Words
Homework
 Chapter 5 Mastering Biology Website
- All Membrane Function Activities
- Fill in Bioflix study sheet for membrane
transport
 Mastering Biology Activities (minimum)
- Energy Transformations
- The Structure of ATP
- How Enzymes Work
 Read Bill Bryson Excerpt in study notes
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Energy
Kinetic Energy
Potential Energy
Metabolism
Enzyme
Induced Fit
Respiration
Breathing
ATP (Adenosine Triphosphate)
ADP (Adenosine Diphosphate)
 Revise for Test A Topics 1-6
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