Download Metabolism

Chapter 8
An Introduction to Metabolism
Remember These!
I. Identify forms of energy and energy transformations.
II. Recognizes the laws of thermodynamics
III. Recognize that organize live at the expense of free energy
IV. Relate Free-energy to metabolism
V. Identify exergonic and endergonic reactions. Define catabolism
and anabolism and relate them to metabolism
VI. Explain the structure and hydrolysis of ATP
VII. Recognize how ATP works and is coupled to metabolism
VIII.Recognize how ATP is regenerated
Metabolism
• Metabolism:
•
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The totality of an organism’s chemical processes
From food to energy.
• Concerned with managing the material and energy
resources of a cell
Metabolism
• Organization of living life into Metabolic Pathways.
Catabolism vs. Anabolism
• Catabolic Pathways:
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Release energy by breaking down complex molecules to simpler
ones
Example: cellular respiration
• Anabolic Pathways:
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Consume energy to build complicated molecules from simpler
ones
Example: Synthesis of a protein from AAs
Bioenergetics
• Bioenergetics:
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The study of how
organisms manage
their energy resources
• Energy = the capacity
to do work
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Kinetic energy: the
energy of motion
Potential energy: stored
energy
Laws of Thermodynamics
• 1st Law of Thermodynamics:
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Energy can be transferred and transformed, but it can be neither
created nor destroyed.
• 2nd Law of Thermodynamics:
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Every energy transfer or transformation increases the entropy of
the universe.
Energy
• Spontaneous process:
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A change that can occur without outside help
• Free energy:
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The portion of a system’s energy that can perform work when
temperature is uniform throughout the system, as in a living cell
Called “free” because it is available to do work
Exergonic vs. Endergonic Reactions
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Exergonic Reactions
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Proceed with a net release of free energy
“downhill”
Occur spontaneously
Example: cellular respiration
Endergonic Reactions
•
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Reactions that absorb free energy from their surroundings
“uphill”
Do NOT occur spontaneously
Example: photosynthesis
Exergonic vs. Endergonic Reactions
ATP
•
•
All cellular work requires ATP!
Triphosphate tail is unstable
•
•
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3 phosphate groups attached to the ribose
Bonds between phosphate groups are unstable and are broken by
hydrolysis
ADP + P is more stable than ATP
•
Therefore, this is a downhill (exergonic) reaction!
ATP has to be regenerated…
•
Cellular respiration!
ATP
Enzymes
• Enzymes
•
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Catalytic proteins
Catalyst = a chemical agent that changes the rate of a reaction
without being consumed by the reaction
Enzymes
• Activation Energy
•
•
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The energy required to
break the bonds in the
reactant molecules
Heat helps… but cannot be
used in cells
Why not?
• Enzymes can only speed
up reactions that would
eventually occur anyways
Selectivity of Enzymes
• Enzymes are VERY selective
• Substrate = the reactant an enzyme acts on
•
Enzyme binds to the substrate(s) and converts the substrate(s)
to the product(s)
• Enzymes can distinguish its substrate from closely related
compounds so each type of enzyme catalyzes a particular
reaction
Enzyme Structure
• Active site:
•
The part of the enzyme that actually binds to the substrate
• Induced Fit:
•
As a substrate enters the active site, it induces the enzyme to
change its shape slightly so that the active site fits even more
snugly around the substrate
Enzymes
Enzymes
• How they speed up a reaction…
•
•
Put 2 substrates together (blind date)
Create a microenvironment conducive to a particular reaction
(ie. Low pH)
Enzyme Rate of Reaction
• Rate of Reaction:
•
Partly a function of the initial concentration of a substrate
•
•
More substrate = more frequently access active sites of enzyme
There is a limit to this…
• Sometimes all enzymes are “busy”
• Enzyme is said to be “saturated”
•
Every enzyme has an optimal temperature and pH level
Enzymes
• Cofactors:
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Nonprotein helpers required along with enzymes for catalytic
activity
•
zinc, iron, copper, vitamins, etc.
Enzymes
•
Enzyme Inhibitors:
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Certain chemicals selectively inhibit
the action of specific enzymes
Competitive inhibitors:
•
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Mimics that compete with
normal substrate molecules for
admission into the active site
Noncompetitive inhibitors:
•
Impede enzymatic reactions by
binding to a part of the enzyme
away from the active site,
thereby making the enzyme
change its shape
Enzymes
•
Allosteric site:
•
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A specific receptor site on some part of the enzyme molecule remote
from the active site to which the molecules that naturally regulate
enzyme activity bind
Act as valves that control rates of key reactions in metabolic pathways
On/Off switch
Enzymes
• Cooperativity
•
•
One substrate molecule
primes an enzyme to
accept additional
substrate molecules
Favorable
conformational change
in one subunit of an
enzyme changes all the
others too
Enzymes
• Feedback Inhibition:
•
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A metabolic pathway is
switched off by its end
product, which acts as
an inhibitor of an
enzyme within the
pathway
Thermostat