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Chapter 6 - An Introduction to Metabolism


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the totality of an organism’s chemical processes; an emergent property of life that arises from specific interactions between molecules within the orderly environment of the cell
Catabolic pathways
Degradative processes in which complex molecules are broken down into simpler molecules; one major component of catabolism is cellular respiration, in which sugar glucose is broken down into carbon dioxide and water
Anabolic pathways
Processes that consume energy to build complicated molecules from simpler ones (e.g. synthesis of proteins from amino acids)
Energy coupling
the use of an exergonic process to drive an endergonic process
the study of how organisms manage their energy resources
the capacity to do work; the ability to rearrange a collection of matter
Kinetic Energy
the energy of motion
Potential Energy
the energy that matter possesses because of its location or structure
Chemical Energy
a form of potential energy; stored in molecules because of the structural arrangement of the atoms in those molecules
the study of energy transformation that occur in a collection of matter
First law of thermodynamics
states that the energy of the universe is constant; energy can be transferred and transformed, but it can be neither created nor destroyed
Second law of thermodynamics
every energy transfer or transformation increases the entropy (disorderliness) of the universe; an organism takes in organized forms of matter and energy from the surroundings and replaces them with less ordered forms; when a spontaneous process occurs in a system, the stability of that system increases (e.g. when water flows downhill, its system increases in stability)
Free energy
the portion of a system’s energy that can perform work when temperature is uniform throughout the system; free energy (G) = the system’s total energy (H) – temperature Kelvin (T) x entropy (S)
Exergonic Reation
a reaction that proceeds with a net release of free energy; spontaneous reactions
Endergonic Reaction
a reaction that absorbs free energy from the surroundings; nonspontaneous reactions
ATP (Adenosine triphosphate)
molecule used to power cellular processes; closely related to one type of nucleotide found in nucleic acids; bonds between phosphate groups can be broken by hydrolysis to yield energy and ADP (adenosine diphosphate)
Phosphorylated intermediate
through the help of enzymes, the free phosphate ion from ATP is transferred to another molecule within the cell; this avoids loss of the free energy and is the key to energy coupling within the cell; this intermediate is more reactive than the original molecule
catalytic proteins
a chemical agent that changes the rate of a reaction without being consumed by the reaction
Activation energy
the energy required to break the bonds in the reactant molecules; initial investment of energy for starting a reaction
the reactant an enzyme acts on
Active site
typically a pocket or groove on the surface of the protein; a limited region of the enzyme that actually binds to the substrate; usually formed by only a few of the enzyme’s amino acids, with the rest of the protein molecule providing a framework that reinforces the configuration of the active site
Induced fit
an induced change in the conformation of the enzyme that allows it to bind more snuggly to the substrate; brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction
nonprotein helpers required by some enzymes for catalytic activity; may be bound tightly to the active site as permanent residents, or they may bind loosely and reversibly along with the substrate; some of these are inorganic compounds
organic cofactors are more specifically called coenzymes
Competitive inhibitors
inhibitors that closely resemble the normal substrate molecule and compete for admission into the active site; reduce the productivity of enzymes by blocking the substrate from entering active sites; this is reversible by increasing the amount of substrate
Noncompetitive inhibitors
inhibitors that do not directly compete with normal substrate at the active site; impede enzymatic reactions by binding to another part of the enzyme; causes enzyme to change its conformation, rendering the active site unreceptive to substrate or leaving the enzyme less effective at catalyzing the conversion of substrate to product
Allosteric site
a site remote to the active site where regulatory molecules can bind to an enzyme and change its shape and function
Feedback inhibition
the switching off of a metabolic pathway by its end-product, which acts as an inhibitor of an enzyme within the pathway
if an enzyme has two or more subunits, this interaction with one substrate molecule triggers the same favorable conformational change in all other subunits of the enzyme; amplifies the response of enzymes to substrates
an enzyme that is devoid of its necessary cofactor and is thus catalytically inactive
an enzyme that contains its necessary cofactor and is thus catalytically active
an enzyme that is secreted in an inactive form; cleaved under certain physiological conditions to the active form of the enzyme

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