Download Lab 3: Enzymes

Metabolisms and enzymes
4-11-16
What is a chemical reaction?
• A chemical reaction is a process that forms
or breaks the chemical bonds that hold
atoms together
– Chemical reactions convert one set of
chemical substances, the reactants, into
another set, the products
Chemical energy
• Primary energy source for metabolism is
chemical energy stored in bonds
– In animals = food molecules
– In plants = photosynthesis
• More bonds means
more energy stored
• Why fat is high in
calories
Photosynthesis and cellular
respirantion
• Photosynthesis – generates glucose
– Sun energy transformed to energy carrier molecules
like ATP and NADPH
• Cellular respiration – consumes glucose
– Eating glucose and breathing oxygen uses the energy
in the bonds to generate energy carrier molecules
Types of chemical reactions
• All chemical reactions either release
energy or require a net input of energy
– Exergonic: releases energy
– Endergonic: requires a net input of energy
• The terms exothermic and endothermic relate
to the overall exchange of heat during a process
Exergonic reactions
• Reactants have more energy than products
• Energy is released in these reactions
• Ex: Sugar + O2  CO2 + H2O
• Releases energy and heat
Endergonic reactions
• Reactants have less energy than products
• Synthesizing complex biological molecules
requires energy
Another way of seeing the
reactions
Metabolic pathways
• The sum of all the chemical reactions
inside a cell is its metabolism
• Series of interconnected biochemical
reactions
• Convert a substrate molecule or molecules,
through a series of metabolic
intermediates, into a final product
Initial reactant
Intermediates
End products
PATHWAY 1
enzyme 1
enzyme 2
enzyme 3
enzyme 4
PATHWAY 2
enzyme 5
enzyme 6
Peppermint
Types of pathways
• Anabolic – require an input of energy
– To synthesize complex molecules from simpler ones
• Catabolic – generates energy
– To break down complex molecules to simpler ones
Chemical reactions in the body
• Metabolic reactions are an “uphill
battle”
• Energy must be put in to drive reaction
– True even if energy is released in reaction
Potential energy
• Minimum energy required = activation
energy (Ea)
Chemical reactions in the body
• Ea can be overcome by increasing
temperature
– But we would cook!
• At body temperature, metabolic reactions
proceed too slowly to sustain life
– And yet we live!
• Nature has found a way around this
What are catalysts?
• Catalysts are molecules that speed up the
rate of reaction w/out being used up or
permanently altered
What do catalysts do?
• Catalysts speed up the reaction by
lowering up the activation energy required
for the reaction to begin
Activation energy
• A small amount of energy needed for
exergonic reactions to occur (EA)
• Bonds that will break and release energy
need to get into the correct state
• This contorted state is called the
transition state
– High-energy
– Unstable
What are enzymes?
•
•
•
•
Biological catalysts
Mainly proteins
They speed up only exergonic reactions
The majority catalyze one single reaction
– Leaving similar substrates unchanged
enzyme substrate
enzymeproduct(s
• Video
Enzyme structures allow them
to catalyze specific reactions
• Each enzyme has a pocket called an active
site into which one or more reactant
molecules, called substrates, can enter
Enzyme structures allow them
to catalyze specific reactions
• The amino acid sequence + folding of the
protein chains  distinctive shape and
distribution of electrical charge
Enzyme structures allow them
to catalyze specific reactions
• The distinctive shape of the active site is
both complementary and specific to
the substrate
Enzyme structures allow them
to catalyze specific reactions
• In summary, active site amino acids bind
to the substrate and distort bonds to
facilitate a reaction
Enzymes are proteins, so…
• What is it called when a protein looses its
shape and hence its function?
• What can cause that?
substrates
active site
of enzyme
enzyme
product
Substrates enter
the active site in a
specific orientation
The substrates, bonded
together, leave the enzyme;
the enzyme is ready for a
new set of substrates
The substrates and
active site change shape,
promoting a reaction
between the substrates
Cofactors and coenzymes
• Many enzymes don’t work optimally, or even at all, unless
bound to cofactors or coenzymes
• Binding to these molecules promotes optimal conformation 
proper function
• Cofactors are inorganic ions such as iron (Fe++) and
magnesium (Mg++)
– DNA polymerase requires zinc ions (Zn++) to function
• Coenzymes are organic helper molecules
– The most common sources of coenzymes are dietary vitamins
– Some vitamins are precursors to coenzymes and others are
coenzymes
– Vitamin C is a coenzyme for multiple enzymes when building
collagen
Enzyme activity regulation
• pH
– Enzyme structure is distorted (denatured)
when pH is too high or low
Enzyme activity regulation
• Salt concentration
– Salt ions can bind with key amino acids in
enzymes, influencing three-dimensional
structure and destroying function
Enzyme activity regulation
• Temperature
– Low temperatures slow down molecular
movement
– High temperatures cause enzyme shape to be
altered, destroying function
– Most enzymes function optimally only within
a very narrow range of these conditions
fast
For trypsin, maximum
activity occurs at
about pH 8
For pepsin, maximum
activity occurs at
about pH 2
For most cellular
enzymes, maximum
activity occurs
at about pH 7.4
rate
of
reaction
slow
0
1
2
3
4
5
6
Effect of pH on enzyme activity
7
8
9
10
fast
For most human enzymes,
maximum activity occurs
at about 98.6F (37C)
rate
of
reaction
slow
32
0
104
68
20
40
temperature
140 (F)
60 (C)
Effect of temperature on enzyme activity