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Metabolism
Cell Energetics
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Cell do three main kinds of work
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Mechanical – move themselves
Transport – move something else
Chemical – convert stuff to other stuff
Work requires energy
Where does the energy come from and how
do cells use it?
Cell Energetics
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Energy is ______
Metabolism
2 types of metabolism
Two forms of energy
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How do cells use the 2 forms
2 Laws of Thermodynamics
Entropy
2 types of reactions
Cell Energetics
Metabolism = total of all the chemical
reactions taking place in an organism
Metabolism
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Anabolism = ‘build up’ processes;
‘consume’ (store) energy by assembling
macromolecules
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Photosynthesis
Catabolism = ‘break down’ reactions;
release energy by breaking down (lyse)
molecules
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Digestion
Energy
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Energy – the ability to do work
Potential = capacity to do work
(move something); due to
position or stored (chemical
energy; glucose, glycogen)
Kinetic = motion
Equilibrium = energy runs out
Kinetic and potential energy
What does the types of energy have to do with biology?
Thermodynamics
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1st Law – energy cannot be created nor
destroyed
 Energy can be transformed
2nd Law – ‘Law of Entropy’ whenever energy is
transformed, some of it becomes ‘unusable’
Entropy - amount of usable energy decreases
each time it is used
 ‘Lost’ as heat
 Energy is running down, universe is tending
towards disorder
Biological Order and Disorder
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Organisms are open systems
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Use energy to maintain order and organization
Trade organization for heat (increase entropy in
the environment)
Metabolism: Reactions
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Two types of reactions:
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Exergonic, endergonic
Exergonic reaction - release of free
energy
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Less stable, more work
Fire, respiration
Metabolism: Reactions
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Endergonic reaction - energy is
absorbed/stored
 Photosynthesis
Chemical Reactions
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Equilibrium is
eventually reached
in closed systems
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Reduced free energy
No work is done
You’re dead!
What cells do..
Review
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What are the 2 forms of energy?
_____ is the ability to do work
Energy is lost in chemical reactions as __
A reaction that stores/absorbs energy is
said to be _____
A reaction that releases energy is _____
The total of all chemical reactions in an
organism is called ____
Coupled Reactions
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Living systems use coupled reactions
 Endergonic reactions are linked
(coupled) with exergonic reactions
Energy from an exergonic reaction
(respiration) is stored in chemical bonds
Coupled Reactions
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ATP – Adenosine triphosphate
Cyclical
Catabolic pathways drive the regeneration
of ATP from ADP and phosphate
Controlled by enzymes
Uses of Energy
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Mechanical - moving of
cilia/flagella, muscle,
cytoplasm, chromosomes
(mitosis), mousetrap
Transport - H+ ‘pump’, receptors
Chemical – polymerization
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Bioluminescence
• Enzymes control metabolism –
If enzymes are present, reactions
take place, if not, they don’t.
Enzymes speed up reactions by
lowering activation energy
Enzymes
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Biological catalysts
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Accelerate a reaction without being changed
Proteins (700)
Catabolic or anabolic reactions
Enzymes
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All chemical reactions require
activation energy
Activation energy (EA) - the
initial amount of energy needed
to start a chemical reaction
Transition state = reactants have absorbed energy
 Have become unstable
 Reaction takes place
Enzymes
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Some reactions occur
spontaneously due to heat
from the environment (rust)
Cellular T needs to remain
low
Metabolism is too slow at
low T
 Starch to glucose
Enzymes used to reduce
activation energy
(metabolism at lower T)
Enzymes
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Substrate = substance enzyme acts on
Active site = area on the enzyme where
substrate binds
 Verryyy specific
 Groove, pocket = 3d shape
Enzymes
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Lock and key mechanism
Induced Fit = enzyme may change shape to
allow better reaction on substrate
Factors That Affect Enzyme Activity
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Temperature
pH
Inorganic salts –
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Disrupt H bonds, ionic bonds, hydrophobic
interactions
Cofactors
Inhibitors
Temperature
and pH affect
enzyme
activity
Cofactors
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Cofactors - nonprotein enzyme helpers
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Metals – Fe, Zn, Cu
Coenzymes - organic cofactors
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Vitamins
Enzymes
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Inhibitors = substances that inhibit the
actions of enzymes (2 kinds:)
 Competitive inhibitors
 Noncompetitive inhibitors
Competitive inhibitors resemble substrate,
block active site
Neurotoxin, Disulfiram
Enzymes
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Noncompetitive
inhibitors - causes
enzyme to change
shape
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Destroys conformation
(active site)
DDT, nerve gas (DSF)
May be allosteric
regulation
Allosteric Regulation of Enzymes
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Allosteric regulation - a protein’s
function at one site is affected by
binding of a regulatory molecule at
another site
Receptor site located away from
the active site (quatenary
structure)
Allosteric site has to be activated,
(may be inhibited)
Allosteric activator
Allosteric inhibitor
Enzymes
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Cooperativity - one
substrate molecule can
activate all other subunits
of an enzyme
 Induced fit
Only requires a small
concentration of substrate
to activate enzyme
Enzyme Activity Helps Control
Metabolism
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A cell’s metabolic pathways must be tightly
regulated
DNA codes for proteins (enzymes)
Amount of enzyme can determine rate of
reaction
Feedback Inhibition - end product of the
pathway inhibits the pathway
Regulation
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Metabolic pathways – series of enzymes
creates small steps to a final product
Controlling the enzymes (activity or
production) controls the pathway and
product(s)
Feedback Inhibition
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Final product of the
pathway shuts off the
pathway
Feedback inhibition
prevents cells from
wasting resources
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“don’t need gas if you
don’t have a car.”
Isoleucine – allosteric
inhibitor