Chapter 6 Metabolism 6.1

ATP is hydrolyzed into ADP

ATP is hydrolyzed into ADP

Entropy

An important concept in physical systems is that of order and disorder (also known as randomness). The more energy that is lost by a system to its surroundings, the less ordered and more random the system is. Scientists refer to the measure of randomness or disorder within a system as entropy.

Living Cells are highly ordered

As a system becomes more disordered, the lower its energy and the higher its entropy become.

Entropy

High entropy means high disorder and low energy

Transition state

However, to get them into a state that allows the bonds to break, the molecule must be somewhat contorted. A small energy input is required to achieve this contorted state. This contorted state is called the transition state, and it is a high-energy, unstable state.

Endergonic

If a chemical reaction requires an input of energy rather than releasing energy, then the ∆G for that reaction will be a positive value. In this case, the products have more free energy than the reactants. Thus, the products of these reactions can be thought of as energy-storing molecules. An endergonic reaction will not take place on its own without the addition of free energy. They are non spontaneous.

exergonic reactions

Reactions that have a negative ∆G and consequently release free energy are called exergonic reactions. Think: exergonic means energy is exiting the system.

Activation energy

The activation energy of a particular reaction determines the rate at which it will proceed. The higher the activation energy, the slower the chemical reaction will be. The example of iron rusting illustrates an inherently slow reaction

Substrate

The chemical reactants to which an enzyme binds are the enzyme's substrates.

Heat energy

Thermodynamically, heat energy is defined as the energy transferred from one system to another that is not doing work. For example, when an airplane flies through the air, some of the energy of the flying plane is lost as heat energy due to friction with the surrounding air.

Activation energy

This small amount of energy input necessary for all chemical reactions to occur is called the activation energy (or free energy of activation) and is abbreviated

equilibrium

This state of equilibrium is one of the lowest possible free energy and a state of maximal entropy. Energy must be put into the system to push the reactants and products away from a state of equilibrium. Either reactants or products must be added, removed, or changed. If a cell were a closed system, its chemical reactions would reach equilibrium, and it would die because there would be insufficient free energy left to perform the work needed to maintain life.

Heat energy

Where does the activation energy required by chemical reactants come from? The source of the activation energy needed to push reactions forward is typically heat energy from the surroundings.

active site

active site specific region of the enzyme to which the substrate binds

ATP

adenosine triphosphate, the cell's energy currency

phosphoanhydride bond

bond that connects phosphates in an ATP molecule

denature

denature process that changes the natural properties of a substance

exergonic

describes chemical reactions that release free energy

induced fit

dynamic fit between the enzyme and its substrate, in which both components modify their structures to allow for ideal binding

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

Heat

energy energy transferred from one system to another that is not work (energy of the motion of molecules or particles)

ATP

energy-releasing reactions are powered by...........?

The rusting of iron is an

example of a spontaneous reaction that occurs slowly, little by little, over time.

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

cofactor

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

metabolic pathway

is a series of interconnected biochemical reactions that convert a substrate molecule or molecules, step-by-step, through a series of metabolic intermediates, eventually yielding a final product or products

ATP

is a small, relatively simple molecule (Figure), but within some of its bonds, it contains the potential for a quick burst of energy that can be harnessed to perform cellular work. This molecule can be thought of as the primary energy currency of cells in much the same way that money is the currency that people exchange for things they need. ATP is used to power the majority of energy-requiring cellular reactions.

entropy (S)

measure of randomness or disorder within a system

Catabolic

pathways involve the degradation (or breakdown) of complex molecules into simpler ones. Molecular energy stored in the bonds of complex molecules is released in catabolic pathways and harvested in such a way that it can be used to produce ATP

Anabolic

pathways require an input of energy to synthesize complex molecules from simpler ones. Synthesizing sugar from CO2 is one example

Thermodynamics

refers to the study of energy and energy transfer involving physical matter. The matter and its environment relevant to a particular case of energy transfer are classified as a system, and everything outside of that system is called the surroundings. For instance, when heating a pot of water on the stove, the system includes the stove, the pot, and the water. Energy is transferred within the system (between the stove, pot, and water). There are two types of systems: open and closed. An open system is one in which energy can be transferred between the system and its surroundings. The stovetop system is open because heat can be lost into the air. A closed system is one that cannot transfer energy to its surroundings.

coenzyme

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

thermodynamics

study of energy and energy transfer involving physical matter

bioenergetics

study of energy flowing through living systems

If energy is released during a chemical reaction

then the resulting value from the above equation will be a negative number. In other words, reactions that release energy have a ∆G < 0. A negative ∆G also means that the products of the reaction have less free energy than the reactants, because they gave off some free energy during the reaction.

kinetic energy

type of energy associated with objects or particles in motion

competitive inhibition

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

substrate

which the enzyme acts