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  

Next  slide  

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  

€

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  

€

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