slide 8 Flashcards
Metabolism
The Energy of Life
The living cell
• Is a miniature factory where thousands of
reactions occur
• Converts energy in many ways
Metabolism
- Includes all of an organism’s chemical reactions
- Is a network of pathways
- Arises from interactions between molecules
An organism’s metabolism transforms
matter and
energy subject to the laws of thermodynamics
A metabolic pathway has many steps
These begin with a specific molecule or
molecules and end with a specific product
Each step is facilitated by a specific catalyst
A catalyst
is a substance that accelerates the rate of a chemical reaction without affecting the products of the reaction and without itself being altered or consumed by the reaction.
enzymes.
The catalysts in living
organisms are proteins called
enzymes
Metabolic pathways balance supply and demand.
• Speed up reactions when not enough product is present
• Slow down reactions when a surplus of product is present
• Products in one set of reactions are the starting molecules
in other sets of reactions.
Catabolic pathways
• Break complex molecules into simpler ones
• Release energy
e.g. hydrolysis
reactions
Anabolic pathways
• Build complicated molecules from simpler ones
• Consume energy
e.g. dehydration
reactions
Energy
– Is the capacity to cause change
– Exists in various forms, some can perform work
Kinetic energy
– Is the energy associated with motion
Potential energy
– Is stored in the location of matter
– Includes chemical energy stored in molecular
structure (chemical bonds)
There are many forms of energy
(light, heat, chemical, electrical,
etc.) but only two states:
Potential energy is stored energy
Kinetic energy is the energy
present in the motion of a body
1st law of thermodynamics
- energy is neither
created or destroyed, but can be transformed
from one form to another
2nd law of thermodynamics -
physical systems
tend to proceed to a state of greater disorder
(entropy)
Energy enters a biological system
is spent, transformed, and lost as heat.
Gibbs free energy is the energy available for
work in a system at uniform temperature.
Josiah Willard Gibbs
1839-1903
The free-energy change of a reaction tells us
whether the reaction occurs spontaneously.
During a spontaneous change free energy
decreases and the stability of a system increases
Spontaneous change:
- The free energy of the system decreases - The system becomes more stable - The released free energy can be harnessed to do work
exergonic reactions.
The majority of the reactions in living cells release
free energy and are called exergonic reactions.
endergonic reactions.
Many important reactions in cells, however,
require the addition of energy and are called
endergonic reactions
equilibrium,
Reactions in a closed system eventually reach
equilibrium, and can do no more work.
Equilibrium and Metabolism
Cells in our body experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium
Cellular metabolism
is an open, multi-step process
Entropy (disorder)
is decreased in living organisms
by metabolic processes, but this results in increased
entropy of the larger system.
Entropy (disorder)
is decreased in living organisms
by metabolic processes, but this results in increased
entropy of the larger system.
• Just because a reaction is exergonic, and therefore
occurs spontaneously, does not mean it occurs rapidly.
• Even exergonic reactions require destabilization of
chemical bonds through the input of activation energy
Enzymes catalyze
reactions
by lowering the EA barrier
enzyme’s substrate.
The reactant that an enzyme acts on is
called the enzyme’s substrate.
enzyme-substrate complex
The enzyme binds to its substrate, forming
an enzyme-substrate complex.
The active site
is the region on the enzyme
where the substrate binds
The active site can lower an EA barrier by
- Orienting substrates correctly
- Straining substrate bonds
- Providing a favorable microenvironment
- Covalently bonding to the substrate
Each enzyme has an optimal temperature
in which it can function properly
Each enzyme has an optimal pH
in which it can function properly
Cofactors
are nonprotein enzyme helpers
Cofactors may be
inorganic (such as a metal
in ionic form) or organic
coenzyme
An organic cofactor is called a coenzyme
Coenzymes include vitamins.
Competitive inhibitors
bind to the active site of
an enzyme, competing with the substrate.
Noncompetitive inhibitors
bind to another part
of an enzyme, causing the enzyme to change
shape and making the active site less effective.
Allosteric regulation
occurs when a regulatory
molecule binds to a protein at one site and affects
the protein’s function at another site.
Metabolism can be regulated by switching
on or
off the genes that encode specific enzymes or by
regulating the activity of enzymes
Cooperativity
is a form of allosteric regulation
that can amplify enzyme activity
Cooperativity
is a form of allosteric regulation
that can amplify enzyme activity
One substrate molecule primes
an enzyme to act
on additional substrate molecules more readily.
Allosteric regulators are attractive drug
candidates for enzyme regulation because of
their specificity
Inhibition of proteolytic enzymes called caspases
may help management of inappropriate
inflammatory responses
In feedback inhibition,
the end product of a
metabolic pathway shuts down the pathway
Feedback inhibition prevents a cell from wasting
chemical resources by synthesizing more product
than is needed
Location of Enzymes
Structures within the cell help bring
order to metabolic pathways.
Some enzymes act as structural
components of membranes
In eukaryotic cells, some enzymes
reside in specific organelles.
Changes (mutations) in genes lead to changes
in amino acid composition of an enzyme
Altered amino acids in enzymes may alter their
substrate specificity
Lab experiments have been successful in
altering the function
of β–galactosidase from
the bacterium E. coli.
