Intro to biochemistry
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Transcript of Intro to biochemistry
Biochemistry 461 Fall, 2015 Lecture 1
Introduc<ons & Review of some chemistry
Reading & Problems: Please see the syllabus
Helpful site for review: hHp://www.biology.arizona.edu/
biochemistry/
Hyponatremia in Athletes
The Goal of Biochemistry: Understanding biology at the chemical
level.
Biochemistry in the Grand Scheme Anatomy & Physiology
Cell Biology
Biochemistry
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Organism
Organ
Cell
Organelle
Biochemistry: Structure & Func<on of Macromolecular Complexes and
Macromolecules
Transfer RNA Glucokinase Lipid Cellulose
Nucleosome Ribosome
Chemistry
Chemistry
General Structure Specific Example
STRUCTURE & NONCOVALENT BONDS
THERMODYNAMICS:What is possible?
The power of thermodynamics lies in its ability to provide informa<on about
what is possible. ΔG provides informa<on about
spontaneity ΔG<0-‐Favorable Process, exergonic
ΔG>0-‐Unfavorable Process, endergonic
Energy Flow in Organisms
Energy
Enthalpy
Entropy
Gibbs free energy comes in two forms
• ΔG=ΔH-‐TΔS
• ΔH-‐enthalpy: heat transferred at constant pressure
For our purposes this means the energy of bond breakage and forma<on
• ΔS-‐entropy: a measure of disorder
• Temperature is also important
Example:Why does NaCl readily dissolve in Water?
Halobacteria: Can live in 5M salt
hHp://www.brasdelport.com/wp-‐content/gallery/halobac1/halobact1.jpg
Likes 4M salt!
Why does sodium chloride dissolve so readily in water?
• Salt crystals are very stable with strong inter-‐ionic interac<ons:
Bond Exchange in Dissolving a Salt
For NaCl the ΔHsoln=+3.87 kJoule/mol in water at 25oC
SO WHY DOES NaCl DISSOLVE SO EASILY IN WATER?
Entropy Rules!
The sodium and chloride ions have more disorder when dissolved.
Spontaneity is determined by both enthalpy and entropy
ΔG=ΔH-‐TΔS
Mul<ple possible combina<ons of enthalpy and entropy can result in a spontaneous reac<on. Measurements of the enthalpy and entropy can provide clues about the structural origins of the favorable free energy.
Units of Energy typically used in Biochemical Thermodynamics
• Energy unit: 1 cal = 4.184 J: so 1 kcal/mol = 4.184 kJoule/mole
• Enthalpy: kcal/mol or kJ/mole • Entropy: cal/mol-‐K or J/mole-‐K
• Cal: calorie • J:Joule (named for James PrescoH Joule) • K-‐Temperature in Kelvin
Energy and Chemistry Standard Free Energy Changes for
Chemical Reac<ons, ΔGo, at equilibrium
• Gibbs: ΔGo = -‐RT ln Keq • Rewrite: Keq = exp(-‐ΔGo/RT)
• Keq is equilibrium constant; formula depends on reac<on type
• For aA + bB → cC + dD, Keq = ([C]c[D]d)/([A]a[B]b)
• For Biochemical reac<ons the standard state ΔG’o and K’eq refer to pH7.0 and [H2O]=55.5M, 25oC, and ini<al concentra<ons of each component at 1M.
Example
• ATP + H2O ADP + Pi ΔG’o=-‐7.3 kcal/mol -‐30.5 kJ/mol
• What is the equilibrium constant?
Role of Reactant Concentra<ons
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ΔG = ΔG'o +RT ln [C]c[D]d
[A]a[B]b
How does the reac<on proceed if the quo<ent of the reactant and product concentra<ons are far from equilibrium?
What happens when equilibrium is reached?
• Dependence of ΔG on Concentra<ons
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ΔG = ΔG'o +RT ln [C ]c[D]d
[A]a[B]b
Q =[C ]c[D]d
[A]a[B]b
[Reactants]>>[Products], ΔG<ΔG’o
[Reactants]<<[Products], ΔG>ΔG’o
Think about how in the cell the Gibbs Free Energy for a reac<on can be made more favorable.
Coupled reac<ons ;An unfavorable reac<on can be driven by a favorable
reac<on.
The favorable or exergonic movement of the large weight pays for raising the smaller weight.
Chemical Example
A Brief Word about Kine<cs: Thermodynamics may indicate that a process is possible. However, it mat be very slow-‐or have a very large
barrier associated with it.
Enzymes Speed up Reac<ons by Lowering the Energe<c Barrier that separates reactant Reactant from Product