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activation energy
energy necessary for reactions to occur
active site
enzyme's specific region to which the substrate binds
allosteric inhibition
inhibition by a binding event at a site different from the active site, which induces a conformational change and reduces the enzyme's affinity for its substrate
anabolic (also anabolism)
pathways that require an energy input to synthesize complex molecules from simpler ones
ATP
adenosine triphosphate, the cell's energy currency
bioenergetics
study of energy flowing through living systems
catabolic / catabolism
pathways in which complex molecules break down into simpler ones
chemical energy
potential energy in chemical bonds that releases when those bonds are broken
coenzyme
small organic molecule which are required to enhance an enzyme's activity
cofactor
inorganic ion, such as iron and magnesium ions, required for optimal enzyme activity regulation
competitive inhibition
type of inhibition in which the inhibitor competes with the substrate molecule by binding to the enzyme's active site
denature
process that changes a subtance's natural properties
endergonic
describes chemical reactions that require energy input
enthalpy
a system's total energy
entropy (S)
measure of randomness or disorder within a system
exergonic
describes chemical reactions that release free energy
feedback inhibition
a product's effect of a reaction sequence to decrease its further production by inhibiting the first enzyme's activity in the pathway that produces it
free energy
Gibbs free energy is the usable energy, or energy that is available to do work
heat
energy transferred from one system to another that is not work (energy of the molecules' motion or particles)
heat energy
total bond energy of reactants or products in a chemical reaction
induced fit
dynamic fit between the enzyme and its substrate, in which both components modify their structures to allow for ideal binding
kinetic energy
energy type that takes place with objects or particles in motion
metabolism
all the chemical reactions that take place inside cells, including anabolism and catabolism
phosphoanhydride bond
bond that connects phosphates in an ATP molecule
potential energy
energy type that has the potential to do work; stored energy
substrate
molecule on which the enzyme acts
thermodynamics
study of energy and energy transfer involving physical matter
transition state
high-energy, unstable state (an intermediate form between the substrate and the product) occurring during a chemical reaction
acetyl CoA
combination of an acetyl group derived from pyruvic acid and coenzyme A, which is made from pantothenic acid (a B-group vitamin)
aerobic respiration
process in which organisms convert energy in the presence of oxygen
anaerobic
process that does not use oxygen
anaerobic cellular respiration
process in which organisms convert energy for their use in the absence of oxygen
ATP synthase (also F1F0 ATP synthase)
membrane-embedded protein complex that adds a phosphate to ADP with energy from protons diffusing through it
chemiosmosis
process in which there is a production of adenosine triphosphate (ATP) in cellular metabolism by the involvement of a proton gradient across a membrane
citric acid cycle (also Krebs cycle)
series of enzyme-catalyzed chemical reactions of central importance in all living cells for extraction of energy from carbohydrates
dephosphorylation
removal of a phosphate group from a molecule
fermentation
process of regenerating NAD+ with either an inorganic or organic compound serving as the final electron acceptor; occurs in the absence of oxygen
GLUT protein
integral membrane protein that transports glucose
glycolysis
process of breaking glucose into two three-carbon molecules with the production of ATP and NADH
isomerase
enzyme that converts a molecule into its isomer
Citric Acid Cycle (Krebs cycle)
alternate name for the citric acid cycle, named after Hans Krebs, who first identified the steps in the pathway in the 1930s in pigeon flight muscles; see citric acid cycle
oxidative phosphorylation
production of ATP using the process of chemiosmosis in the presence of oxygen
phosphorylation
addition of a high-energy phosphate to a compound, usually a metabolic intermediate, a protein, or ADP
prosthetic group (also prosthetic cofactor)
molecule bound to a protein that facilitates the function of the protein
pyruvate
three-carbon sugar that can be decarboxylated and oxidized to make acetyl CoA, which enters the citric acid cycle under aerobic conditions; the end product of glycolysis
redox reaction
chemical reaction that consists of the coupling of an oxidation reaction and a reduction reaction
substrate-level phosphorylation
production of ATP from ADP using the excess energy from a chemical reaction and a phosphate group from a reactant
ubiquinone
soluble electron transporter in the electron transport chain that connects the first or second complex to the third
absorption spectrum
range of wavelengths of electromagnetic radiation absorbed by a given substance
antenna protein
pigment molecule that directly absorbs light and transfers the energy absorbed to other pigment molecules
Calvin cycle
Light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH
carbon fixation
process of converting inorganic CO2 gas into organic compounds
carotenoid
photosynthetic pigment (yellow-orange-red) that functions to dispose of excess energy
chemoautotroph
organism that can build organic molecules using energy derived from inorganic chemicals instead of sunlight
chlorophyll a
form of chlorophyll that absorbs violet-blue and red light and consequently has a bluish-green color; the only pigment molecule that performs the photochemistry by getting excited and losing an electron to the electron transport chain
chlorophyll b
accessory pigment that absorbs blue and red-orange light and consequently has a yellowish-green tint
chloroplast
organelle in which photosynthesis takes place
cytochrome complex
group of reversibly oxidizable and reducible proteins that forms part of the electron transport chain between photosystem II and photosystem I
electromagnetic spectrum
range of all possible frequencies of radiation
electron transport chain
group of proteins between PSII and PSI that pass energized electrons and use the energy released by the electrons to move hydrogen ions against their concentration gradient into the thylakoid lumen
granum
stack of thylakoids located inside a chloroplast
heterotroph
organism that consumes organic substances or other organisms for food
light harvesting complex
complex that passes energy from sunlight to the reaction center in each photosystem; it consists of multiple antenna proteins that contain a mixture of 300 to 400 chlorophyll a and b molecules as well as other pigments like carotenoids
light-dependent reaction
first stage of photosynthesis where certain wavelengths of the visible light are absorbed to form two energy-carrying molecules (ATP and NADPH)
light-independent reaction
second stage of photosynthesis, through which carbon dioxide is used to build carbohydrate molecules using energy from ATP and NADPH
mesophyll
middle layer of chlorophyll-rich cells in a leaf
P680
reaction center of photosystem II
P700
reaction center of photosystem I
photoact
ejection of an electron from a reaction center using the energy of an absorbed photon
photoautotroph
organism capable of producing its own organic compounds from sunlight
photon
distinct quantity or "packet" of light energy
photosystem
group of proteins, chlorophyll, and other pigments that are used in the light-dependent reactions of photosynthesis to absorb light energy and convert it into chemical energy
photosystem I
integral pigment and protein complex in thylakoid membranes that uses light energy to transport electrons from plastocyanin to NADP+ (which becomes reduced to NADPH in the process)
photosystem II
integral protein and pigment complex in thylakoid membranes that transports electrons from water to the electron transport chain; oxygen is a product of PSII
pigment
molecule that is capable of absorbing certain wavelengths of light and reflecting others (which accounts for its color)
primary electron acceptor
pigment or other organic molecule in the reaction center that accepts an energized electron from the reaction center
reaction center
complex of chlorophyll molecules and other organic molecules that is assembled around a special pair of chlorophyll molecules and a primary electron acceptor; capable of undergoing oxidation and reduction
reduction
gain of electron(s) by an atom or molecule
spectrophotometer
instrument that can measure transmitted light and compute the absorption
stoma
opening that regulates gas exchange and water evaporation between leaves and the environment, typically situated on the underside of leaves
stroma
fluid-filled space surrounding the grana inside a chloroplast where the light-independent reactions of photosynthesis take place
thylakoid
disc-shaped, membrane-bound structure inside a chloroplast where the light-dependent reactions of photosynthesis take place
thylakoid lumen
aqueous space bound by a thylakoid membrane where protons accumulate during light-driven electron transport
wavelength
distance between consecutive points of equal position (two crests or two troughs) of a wave in a graphic representation; inversely proportional to the energy of the radiation