An Introduction to
Metabolism
Flow of energy through life
Life is built on chemical reactions
Chemical Reactions of Life
•
Metabolism
–
Is the
of an organism’s chemical
rxns
–
Forming bonds
between molecules
•
Dehydration synthesis
•
reactions
–
Breaking bonds
between molecules
•
Hydrolysis
•
reactions
Examples
•
Dehydration synthesis
•
Hydrolysis
Examples
The Law of Energy Transformation
•
is the study of energy
transformations
•
A closed system, such as that approximated by
liquid in a thermos, is isolated from its
surroundings
•
In an open system, energy and matter can be
transferred between the system and its
surroundings
•
Organisms are
FIRST LAW OF THERMODYNAMICS
•
According to the
,
the energy of the universe is constant:
–
Energy can be transferred and transformed, but it
cannot be created or destroyed
•
The first law is also called the
SECOND LAW OF THERMODYNAMICS
•
During every energy transfer or
transformation, some energy is unusable, and
is often lost as heat
•
According to the
:
–
Every energy transfer or transformation increases
the
(disorder) of the universe
(a) First law of thermodynamics
(b) Second law of thermodynamics
Chemical
energy
Heat
CO
2
H
2
O
+
Chemical reactions & energy
•
Some chemical reactions
–
Exergonic
–
spontaneous
–
Digesting polymers
–
Hydrolysis = catabolism
–
•
Some chemical reactions
require energy
–
Endergonic
–
Non spontaneous
–
Building
–
Dehydration synthesis = anabolism
–
Products
Endergonic vs. exergonic reactions
Energy & life
•
Organisms require energy to live
•
Energy comes from
–
Coupling
with
–
Example: photosynthesis
–
Usually halves of coupled
rxns
occur in different places
so energy
•
Accomplished with carrier molecule such as ATP
Spontaneous Reactions?
•
If reactions are “downhill”, why don’t they just
happen spontaneously?
–
Because
Activation energy
•
Breaking down large molecules
–
Activation energy
–
Large biomolecules are stable
–
Must
Activation energy
•
•
Usually is
•
Most
reactions occur readily at higher temp.
–
Moves the reaction
High
Low
Energy
content of
molecules
Reducing Activation Energy
•
Catalysts
–
Reduce
Catalysts
•
A cell reduces activation energy by using enzymes
Enzymes
•
Biological catalysts
–
Proteins (very specific shape)
–
Facilitate
•
Increase
•
Reduce
•
Don’t change free energy (
Δ
G
) released or required
–
–
Highly specific
•
–
Control reactions
–
Enzyme activity
Enzymes & substrates
•
Substrate
–
Reactant which
–
Enzyme
-
substrate
complex:
•
Product
–
End
result of
reaction
Enzymes and substrates
•
Enzyme + substrate
Product
–
Sucrase
•
Enzyme breaks
down
•
Binds to sucrose &
breaks disaccharide
into
–
DNA polymerase
•
Enzyme builds
•
Adds nucleotides to
a growing
Lock and Key Model
•
Specific shape of the
and catalyze specific reactions
•
Active Site
–
Enzyme
–
Pocket or groove
–
Substrate (= reactant molecule)
Induced Fit
•
When substrate
,
both substrate
and active site change shape
–
Amino acids
–
Electrical charges distort
•
New product is
expelled and enzyme
can go on and accept
Properties of enzymes
-
Specificity
•
Reaction
Specific
–
Each enzyme is
•
Due to fit between
–
Substrates held in
»
H bonds
»
Ionic bonds
–
Enzymes named for reaction they catalyze
•
Sucrase
breaks down sucrose
•
Proteases
break down proteins
•
Lipases
break down lipids
•
DNA
polymerase builds DNA
•
Pepsin
breaks down polypeptides
Properties of enzymes
-
Reusable
•
Not consumed in reaction
–
Single enzyme molecule can
–
Enzymes
Factors affecting enzymes
–
enzyme
concentration
•
Effect on rates of enzyme
activity
–
As
conc
of enzyme increases,
•
More enzyme = more
–
Reaction rate
•
Substrate becomes
•
Not all enzyme
Factors affecting enzymes
–
substrate
concentration
•
Effect on rates of enzyme
activity
–
As conc. of substrate increases,
•
More substrate =
•
Reaction rate levels off
–
all enzymes have
–
Enzyme
–
Maximum rate of reaction
Factors affecting enzymes
–
temperature
•
Effect on rates of enzyme
activity
–
Optimum Temp
•
Greatest
•
Human enzymes = 35
-
40
º C (body
temp = 37º C)
–
Increase beyond optimum Temp
•
Increased
–
H and ionic bonds = weak bonds
–
Denaturation
=
–
Decrease Temp
•
Molecules
•
Decrease
Factors affecting enzymes
–
temperature
•
Different enzymes function at different
temperatures in different organisms
How do ectotherms do it?
Factors affecting enzymes
–
pH
•
Effect on rates of enzyme
activity
–
Protein shape (conformation)
•
Attraction
–
pH changes
•
Changes charges
•
Disrupt bonds,
–
Most human enzymes are active
at pH 6
-
8
•
Depends
•
Pepsin (stomach)
•
Trypsin
(
Factors affecting enzymes
–
salt
concentration
•
Effect on rates of enzyme
activity
–
Protein shape
(conformation)
•
Depends
–
Salinity changes
•
Change
•
Disrupt bonds,
–
Enzymes intolerant of
extreme salinity
•
Dead Sea is called dead for a
reason!
Factors affecting enzymes
–
Activators
•
Compounds
•
Cofactors
–
Non
-
protein,
•
Mg, K,
Ca
, Zn, Fe, Cu
•
Coenzymes
–
Non
-
protein,
•
Bind temporarily
–
Many vitamins
•
NAD
•
FAD
•
Coenzyme A
Factors affecting enzymes
–
Inhibitors
•
Regulation of enzyme activity
–
Certain chemicals
•
Selective inhibition and
activation
–
Competitive inhibition
–
Noncompetitive inhibition
–
Irreversible inhibition
–
Feedback inhibition
Factors affecting enzymes
–
Competitive
Inhibitors
•
Effect
–
Inhibitor resembles the shape of the
normal
•
Ex
. Penicillin blocks
–
Overcome
by
•
Saturate solution with substrate so it
out
-
competes
Factors affecting enzymes
–
Noncompetitive Inhibitors
•
Effect
–
Inhibitor binds to
•
Allosteric site
•
Called allosteric inhibitor
–
Ex. Some anti
-
cancer drugs inhibit
& therefore in building of
DNA= stop DNA production,
•
Causes
enzyme to
•
Renders
Factors affecting enzymes
–
Irreversible
Inhibitors
•
Inhibitor permanently binds to enzyme
–
Competitor
•
Permanently
–
Allosteric
•
Permanently
•
Ex. Nerve gas,
sarin
, many insecticides (
malathion
,
parathion…)
–
Cholinesterase inhibitors
Factors affecting enzymes
–
feedback
inhibition
•
Regulation & coordination of
production: the end
product of a metabolic pathway shuts down the
pathway
–
Product is
–
Final product is
•
Allosteric inhibitor of earlier enzyme
•
Feedback inhibition
–
No unnecessary accumulation of product
Factors affecting enzymes
–
feedback
inhibition
•
Example
–
Synthesis of amino
acid isoleucine
from amino acid
threonine
Action of Allosteric Control
•
Inhibitors and activators
–
Regulatory molecules
–
Inhibitor keeps enzyme
–
Activator keeps enzyme
Cooperativity
is a form of allosteric regulation that can
amplify enzyme activity
•
Substrate acts as an activator
–
Substrate causes
•
Induced fit
–
Favors binding
–
Makes enzyme
•
Ex. hemoglobin
Metabolic pathways
•
Chemical reactions of
life are organized in
pathways
–
Divide chemical
•
Efficiency
•
Control = regulation
Efficiency
•
Groups of enzymes organized
–
If enzymes are embedded in
membrane
•
Link endergonic
& exergonic
reactions
Industrial Uses of Enzymes
•
Enzymes have long been used for industrial purposes
–
•
Proteases are used to soften hides and remove hair
–
•
Enzymes in barley grains at germinations are used to convert
stored starch to sugars that can be fermented by yeast
–
•
Enzymes are frequently used in genetic engineering
–
•
Some people are “lactose
-
intolerant” (do not produce lactase
in pancreatic juices)
–
cannot digest milk and milk products
–
Lactase is obtained from bacteria
–
Milk and milk products are treated with lactase before
consumption to remove lactose
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