Bio 380 Bioenergetics

Energy definition

Energy is the capacity to do work, or the capacity to cause specific chemical or physical changes. Some changes that need energy are synthetic work, mechanical work, concentration work, electrical work, generation of heat and generation of light.

Thermodynamics deals with the ___ of a system, and is ___ of the pathway of any change between system states. It depends on the ___ at any moment, NOT on the ____ paths from one state to another,

State, independent. Status, transition.

Exchange of energy between a system and its surroundings occurs as either ____ or ____.

Heat, work.

____ is the use of energy to drive a process other than heat flow, and it’s biologically the more useful form of energy transfer.

Work

Three important state variables

Temperature, pressure and volume. They’re relatively constant in most biological systems.

The focus of our system is called the _____, and everything that’s not in the ______ is the ______. The ______ + _______ = the ________ (everything that exists).

System, system, surroundings. System, surrounding, universe.

If a reaction is spontaneous then it ___ happen if they ____ the entropy of the Universe or if they ____ Gibbs free energy of teh system.

can, increase, decrease.

The Second Law of thermodynamics states:

..in every spontaneous physical or chemical process, teh entropy of the Universe increases.

Spontaneous processes move from the ___ probable states to ____ probable states.

less, more.

The second law tells us which direction a process ____ go in.

CAN

Exergonic

Delta G is neg, and the system releases free energy.

Endergonic

Delta G is pos, and the system absorbs free energy.

If delta G is 0, then a reaction is at _____.

Equilibrium.

Spontaneity;

The term spontaneous means that a reaction can take place in the direction indicated. It doesn’t determine that it will take place or how fast it will occur (rate). For a reaction to occur, there must be a delta G < 0 and a favorable path for the reaction to occur.

Synthetic work

Changes in chemical bonds. he work of biosynthesis results in the formation of new chemical bonds and the synthesis of new molecules. biosynthesis is required for growth and maintenance of cells and cellular structures

mechanical work

directional changes in the location or orientation of a cell or a subcellular structure. cytoplasmic streaming or movement of organelles and vesicles along microtubules

concentration work

moving molecules across a membrane against a concentration gradient.

electrical work:

moving ions across a membrane against an electrochemical gradient

generation of heat

Eeleasing heat, generally as a by-product of chemical reactions. While living organisms do not use heat as energy to drive other processes, producing heat is a major use of energy in endotherms.

Systems can be…

isolated, closed, or open

Cells are ____ systems, which means that they exchange _______ with the surroundings>

open, matter and energy.

E = ??

Internal energy; the total energy stored within a system. ΔE = ΔEf - ΔEi or ΔE = ΔEprod - ΔEreactants

The relationship between internal energy and enthalpy is ___. This enthalpy is the energy from ___ converted to ____.

H = E + PV. chemical bonds, heat

If enthalpy (H) is negative..

the reaction is exothermic

If the enthalpy (H) is positive…

the reaction is endothermic

Gibbs Free energy (G)

the measure of the system alone that determines spontaneity. ΔG = ΔH - TΔS.

Spontaneity depends on two competing factors:

1) the enthalpy change (does reaction release or absorb heat?) and

2) the entropy change (does reaction increase or decrease system disorder?), weighted by temperature

A reaction that is endothermic ___ entropy and is ____ spontaneous.

decreases, never.

Equilibrium constant Keq

is the ratio of product concentrations to reactant concentrations for a reaction at equilibrium. Keq= [B]eq / [A]eq

A molar ratio (products to reactants: [B]/[A]) less than Keq means that the reaction will proceed to the ___ to generate more ____.

right, product.

A molar ratio greater than Keq means that the reaction will proceed to the ____ to generate more ____

left, reactant.

Standard free energy change (ΔG°’)

The free energy change under standard temperature, pressure, and concentrations. This applies to conditions that would never occur in biological systems.

ΔG′ provides a measure of how far from equilibrium a reaction is

under the ___ conditions, such as conditions ___.

Specified, in a cell. It is the most useful measure of thermodynamic spontaneity in actual living systems – it is based on the prevailing concentrations of reactants and products.

Thermodynamic spontaneity

A measure of whether or not a reaction or process CAN occur. Entropy (S) and Gibbs Free energy (G) are two alternative means of determining thermodynamic spontaneity.

Kinetic considerations

Kinetics determine the rate of a reaction. If a reaction, product X has lower free energy than substrate Y, so Y —> X is spontaneous and can occur but the path from Y to X goes through a transition state that is at a higher free energy than Y. SO only the subset of.Y molecules that have enough energy to reach the transition state can get over the hurdle and complete the reaction. The rate of the reaction depends on the propotuion of Y that has enough energy at any given time.