bio chapter 8

metabolism

the totality of all chemical reactions occurring within an organism or cell

metabolic pathway

a series of chemical reactions in which a starting molecule is modified through multiple steps to produce a final product

metabolic intermediate

a molecule produced during one step of a metabolic pathway and used in a subsequent step

enzyme

a biological catalyst, usually a protein, that speeds up a specific chemical reaction by lowering its activation energy without being consumed

bioenergetics

the study of how energy flows through living organisms and how organisms transform energy to perform work

energy

the capacity to cause change or perform work

kinetic energy

energy associated with the motion of an object or particle

thermal energy

the kinetic energy associated with the motion of an object or particle

thermal energy

the kinetic energy associated with the random movement of atoms and molecules

heat

thermal energy transferred between objects or systems because of a temperature difference

potential energy

energy stored because of an object’s position, arrangement, or structure

chemical energy

potential energy associated with the arrangement of atoms and electrons in molecules that can be released or transferred during chemical reactions

thermodynamics

the study of energy transformations and transfers

open system

a system that can exchange both energy and matter with its surroundings; organisms are open systems

isolated systems

a system that exchanges neither matter nor energy with its surroundings

first law of thermodynamics

energy cannot be created or destroyed; it can only be transferred or transformed

conservation of energy

the principle that the total amount of energy remains constant even when energy changes forms

second law of thermodynamics

every energy transfer or transformation increases the total entropy of the universe

entropy (s)

measure of the molecular disorder, randomness, or the disperal of energy within a system

energy transformation

the conversion of energy from one form to another, such as chemical energy into kinetic energy or heat

energy transfer

the movement of energy from one object or system to another

spontaneous process

a process that can occur without a continuous input of energy to drive it; it may occur quickly or slowly

nonspontaneous process

a process that requires an input of energy under the specified conditions

biological order

the organized structure of living systems, from molecules to cells and organisms, maintained through every and matter exchanges with the environment

entropy of the universe

the total entropy of a system and its surroundings; it increases during spontaneous processes

free energy- G

the portion of a system’s energy available to perform work then temp and pressure are uniform

gibbs free energy

another name for free energy, used to predict whether a process is spontaneous under specified conditions

change in free energy (ΔG)

the difference between the free energy of the products and the free energy of the reactants; it indicates whether a reaction releases or requires free energy

free-energy equation

ΔG=ΔH-TΔS
where ΔH is the change in enthalpy, T is absolute temperature in kelvins, and ΔS is the change in entropy.

enthalpy-H

a measure of the total heat content of a system at constant pressure; its change reflects energy absorbed or released as heat under those conditions

free-energy sign rule

a negative ΔG indicates a spontaneous, exergonic process; a positive ΔG indicates nonspontaneous endergonic process; ΔG=0 indicates equilibrium

negative ΔG

indicates that a process releases free energy and is spontaneous under the specified conditions

positive ΔG

indicates that a process requires a net input of free energy and is nonspontaneous under the conditions

ΔG=0

indicates that a system is at equilibrium, with no net change in the reaction

exergonic reaction

a chemical reaction that releases free energy, has a negative ΔG, and is spontaneous under the specified conditions

endergonic reaction

a chemical reaction that absorbs free energy, has a positive ΔG, and requires an energy input

reactants

the starting substances in a chemical reaction

products

the substances formed by a chemical reaction

chemical equilibrium

a state in which the forward and reverse reactions occur at equal rates, so there is no net change in the concentrations of reactants and products

dynamic equilibrium

a state in which opposing processes continue to occur at equal rates, producing no net change

metabolic equilibrium

a condition in which metabolic reactions reach equilibrium; living cells generally avoid this state because they continually exchange matter and energy with their surroundings

free-energy gradient

a difference in free energy that can drive a spontaneous process and potentially provide energy for cellular work

energy coupling

the use of energy released by an exergonic process to drive an endergonic process

cellular work

the energy-requiring activities of cells, including chemical synthesis, transport across membranes and mechanical movement

chemical work

the use of energy to drive endergonic chemical reactions such as synthesizing polymers from smaller molecules

transport work

the use of energy to move substances across membranes against their concentration or electrochemical gradients

mechanical work

the use of energy to produce movement, such as muscle contraction, cilia beating, or motor proteins moving along cytoskeletal tracks

atp adenosine triphosphate

the primary energy transfer molecule in cells; atp hydrolysis can provide free energy to drive cellular work

adenine

a nitrogenous base that forms part of atp

ribose

a five-carbon sugar that combines with adenine to form adenosine in atp

triphosphate group

the chain of three phosphate groups in atp

adp- adenosine diphosphate

a molecule containing adenosine and two phosphate groups; it can be converted back into atp by adding an inorganic phosphate using energy

inorganic phosphate (Pi)

a free phosphate group that can be added to adp to form atp or released during atp hydrolysis

atp cycle

the continuous regeneration and breakdown of atp: energy from exergonic processes is used to form atp and atp hydrolysis supplies energy for cellular work

phosphorylation

the transfer or addition of a phosphate group to a molecule

phosphorylated intermediate

a molecule that temporarily receives a phosphate group, often from atp, becoming more reactive and capable of participating in an otherwise unfavorable reaction

atp-driven transport

the use of energy from atp hydrolysis to change a transport protein’s shape and move substances across a membrane

atp-driven mechanical movement

the use of atp hydrolysis to an endergonic reaction so that the combined reaction has a negative net ΔG

catalyst

a chemical agent that increases the rate of a reaction without being consumed overall

catalysis

the process by which a catalyst speeds up a chemical reaction

activation energy- ea

the initial energy required to bring reactants to a transition state so a chemical reaction can proceed

activation energy barrier

the energy barrier that reactants must overcome before bonds can break and form during a reaction

transition state

the unstable, high-energy state that reactants pass through as old bonds break and new bonds form

bond breaking

the separation of atoms previously held together by a chemical bond, which requires energy input

bond formation

the establishment of a chemical bond between atoms, which generally releases energy

enzyme catalysis

the acceleration of a chemical reaction by an enzyme, which lowers the activation energy without changing the reaction’s overall ΔG

substrate

the reactant molecule upon which an enzyme acts

active sites

the specific region od an enzyme where its substrate binds and the catalyzed reaction occurs

enzyme-substrate complex

the temporary structure formed when a substrate binds to an enzyme’s active site

induced fit

a change in an enzyme’s shape after substrate binding that improves the fit between the substrate and active site and facilitates catalysis

enzyme specificity

the ability of an enzyme to recognize particular substrates and catalyze a particular reaction because of the properties of its active site

enzyme catalytic cycle

the sequence in which a substrate binds to an enzyme, catalysis occurs, products are released, and the enzyme becomes available to catalyze another reaction

enzyme reuse

the ability of an enzyme to catalyze multiple reactions because it is not consumed in the reaction

lowering activation energy

the main way enzymes accelerate reactions, allowing more reactant molecules to reach the transition state at ordinary cellular temperatures

enzyme reaction rate

the amount of substrate converted to product per unit of time

substrate concentration

the amount of substrate available to bind to an enzyme; increasing it generally increases reaction rate until the enzymes become saturated

enzyme saturation

the condition in which essentially all available enzyme active sites are occupied by substrate, so adding more substrate no longer substantially increases the reaction rate

enzyme concentration

the amount of enzyme present; increasing enzyme concentration can increase the maximum reaction rate when sufficient substrate is available

optimal temperature

the temperature at which an enzyme functions most efficiently

optimal pH

the pH at which an enzyme has its greatest activity

denaturation

a change in a protein’s three-dimensional structure that disrupts its function, potentially caused by extreme temperatures or pH

temperature effect on enzymes

increasing temperatures generally speeds up molecular movement and reaction rates up to an optimum; excessive heat can denature an enzyme and reduce its activity

pH effect on enzymes

changes in pH can alter the changes and interactions of amino acids, changing the active site’s shape and reducing enzyme activity

pepsin

a digestive enzyme in the stomach that functions best under highly acidic conditions

trypsin

a digestive enzyme that functions best in more alkaline conditions of the small intestine

thermophilic balance

heat-loving bacteria whose enzymes may be adapted to function at temperatures at much higher than those optimal for typical human enzymes

cofactor

a nonprotein helper required by some enzymes for proper catalytic activity; it may be an an inorganic ion or an organic molecule

inorganic cofactor

a nonprotein helper such as a metal ion, including zinc, iron, or copper, that assists enzyme function

coenzyme

an organic cofactor that helps an enzyme catalyze a reaction

vitamin

an organic nutrient that often serves as a coenzyme or provides the raw materials needed to make coenzymes

enzyme inhibitor

a substance that reduces or prevents an enzyme’s activity

competitive inhibitor

a substance that binds to an enzyme’s active site and competes with the substance for access

noncompetitive inhibitors

a substance that binds at a site other than the active site and alters the enzyme’s shape or function, reducing its catalytic activity

allosteric regulation

the regulation of a protein’s activity when a molecule binds to a regulatory site separate from the active site, causing a functional change

allosteric site

a location on a protein where a regulatory molecule binds to change the protein’s activity

allosteric activator

a regulatory molecule that stabilizes an active form of an enzyme or otherwise increases its activity

allosteric inhibitor

a regulatory molecule that stabilizes an inactive form of an enzyme or otherwise decreases its activity

cooperativity

a regulatory mechanism in which substrate binding to one active site changes an enzyme’s shape, increasing the likelihood that substrates will bind to its other active sites

feedback inhibition

a regulatory process in which the final product of a metabolic pathway inhibits an enzyme acting earlier in that pathway, reducing further product synthesis

metabolic regulation

the control of metabolic pathway activity through mechanisms such as enzyme activation, inhibition, and changes in enzyme production