AP Biology Unit 3: Cellular Energetics Key Terms

activation energy

energy necessary for reactions to occur

active site

specific region of the enzyme 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 affinity of the enzyme for its substrate

anabolic

pathways that require an input of energy to synthesize complex molecules from simpler ones

ATP (adenosine triphosphate)

the cell's energy currency

bioenergetics

study of energy flowing through living systems

catabolic

pathways in which complex molecules are broken down into simpler ones

chemical energy

potential energy in chemical bonds that is released when those bonds are broken

coenzyme

small organic molecule, such as a vitamin or its derivative, which is required to enhance the activity of an enzyme

cofactor

inorganic ion, such as iron and magnesium ions, required for optimal regulation of enzyme activity

competitive inhibition

type of inhibition in which the inhibitor competes with the substrate molecule by binding to the active site of the enzyme

denaturation

process that changes the natural properties of a substance

endergonic

describes chemical reactions that require energy input

energy coupling

process during which energy released by one reaction is used to drive another reaction

enthalpy

total energy of a system

entropy (S)

measure of randomness or disorder within a system

exergonic

describes chemical reactions that release free energy

feedback inhibition

effect of a product of a reaction sequence to decrease its further production by inhibiting the activity of the first enzyme in the pathway that produces it

free energy

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 motion of molecules 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

type of energy associated 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

type of energy 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 respiration

process in which organisms convert energy for their use in the absence of oxygen

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

series of enzyme-catalyzed chemical reactions of central importance in all living cells

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

the 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

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

oxidative phosphorylation

production of ATP using the process of chemiosmosis and 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 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 300-400 chlorophyll a and b molecules as well as other pigments like carotenoids

light-dependent reactions

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

a distinct quantity or "packet" of light energy

photosystem

a 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

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