Chapter 3 - Thermodynamic of Biological Systems

Isolated system

no exchange of matter or energy with surrounding environment

Closed system

no exchange of matter, but can exchange energy with environment

Open system

exchange of both matter and energy with the environment is possible

What letter represents the internal energy of a system

E

Equation for change of internal energy of a system (E)

ΔE=Ef-Ei or ΔE=E2-E1

Equation for internal energy of a system under normal conditions

ΔE=q+w

q - heat flow

w - work flow

Equation for work (w)

w= -PΔV

- pressure

- change in volume

Ultimate equation for change in internal energy of a system under normal conditions

ΔE=q-PΔV

Enthalpy (H)

The heat content of a system at constant pressure

Equation for enthalpy (H)

ΔH=ΔE+PΔV

Equation for enthalpy at constant pressure (P=0, therefore PΔV=0)

q=ΔH

Expl. q-PΔV=ΔH

Entropy (s)

randomness/disorder of a system

Equation for entropy (s)

s=Kln(w)

w - # of micro states

K - Boltzman constant - 1.38 x 10^-23 J/K

Entropy equation for energy dispersion

S=dq/T

dq - heat transfer

T - absolute temperature

Standard states

Physical states under standard conditions

1 M concentration

1 atm P

at specific T

Three laws of thermodynamics

1) energy of an isolated system remains constant

2) law of entropy - the entropy of the universe tends to a maximum

3) entropy of a perfect crystal at 0K is 0.

Gibbs free energy equation

ΔG = ΔH - TΔS

What is ΔG°?

standard conditions - change in Gibbs free energy

° indicates standard

ΔG equation under nonstandard conditions?

ΔG=ΔG° + RT ln [B]/[A]

What is the Keq equation for free energy under nonstandard conditions?

Keq = e ^ (-ΔG°/RT)

Every factor of 10 for ΔG° is approximately what?

5.7 KJ/mol, can be used in estimating Keq

If an equation is A-> B + H+, what is the Keq for the system?

Keq = [B-][H+]/[A]

Biological systems are buffered for a pH of

7, or H+ = 10^-7 M

Reactions that produce H+ in biology are more favorable by _ and why?

Biological systems are buffered for a pH of 7, resulting in and ultimate ΔG°' of -40KJ/mol lower than that of a chemical system

What is the symbol ΔG°'? [apostrophe and degrees]

specific standard conditions for biology or biochemistry

KJ/mol for biological systems that consume acid?

+ 40 KJ/mol

KJ/mol for biological systems that produce acid?

- 40 KJ/mol - much more favorable

What does it mean for a molecule to be "high energy"

in biology - favorable to hydrolyzing

NOTHING about bond strength itself !!

What is the isoelectric point?

The pH at which there is no net charge and a molecule is electrically neutral

How do you calculate isoelectric point?

(pK1 + pK2)/2

- average the pkas of the carboxy and amino groups

Which two pkas are used to determine isoelectric point?

Draw out dissociations starting with lowest pka and going to highest, the pkas on either side of the molecule that is NEUTRAL CHARGE are used