How Cells Make ATP                              
   by PHOSPHORYLATION...    adding a phosphate to ADP
                 ADP   +   P    ------>    ATP
   
         a) substrate level phosphorylation...
                 where a substrate molecule ( X-p ) donates its P to ADP making ATP
  

         b) chemiosmosis - [Oxidative Phosphorylation of Krebs cycle & ETC]...
                 food substrates donate e- & protons to acceptor molecules [NADH], i.e., oxidation.
                      NADH gives up electrons & protons are pumped out of mitochondria
                                   (or the chloroplasts in photosynthesis);
                      protons
diffuse back into mito thru an enzyme - ATPase,
                      the ATPase enzyme makes ADP + P  -->  ATP                                  figure * 
                                                                                                                               

         c) photophosphorylation....
                 e- of light energy, instead of food covalent bonds, are captured by chlorophylls
                      to make a proton gradient across the chloroplast membranes...        figure* 
66.gif (249 bytes)               protons move through a chloroplast ATPase enzyme to make ATP


 

 

 

 

   
 
Oxidative Metabolism...  (cell respiration)
          
occurs in heterotrophic organisms that consume foods
                            ... we say organisms oxidize (consume) foods (often glucose) to make energy
                                            because they remove & capture electrons...
                            ... where is energy in foods?     it's in the covalent bonds (e-)
             Thus - METABOLISM is cells capturing e- via REDOX reactions
     

        REDOX   REACTION...    
                             e- passed from one molecule to another [PGAL --> NAD+] in a chemical rx
                             energy is transferred into the new molecule (a redox couple) by holding  e-
  

        OXIDATION  =    removal of electron &/or proton from food covalent bond
  

        REDUCTION   =   gaining electron &/or proton; adds an electron to an acceptor molecule
 
67.gif (173 bytes)        

 

 

 

 

a model redox reaction... 
   
   A-H   +  B-O   
<--->   A  +   B-O-H

       donor            acceptor            (:H)       acceptor          donor
         PGAL                       NAD+                            1,3-bisphosphoglycerate      NADH
  

     reducing           oxidizing                         becomes            becomes
       agent                agent                            oxidized            reduced

   Oxidation state* and energy relationship - more reduced = more energy 

          an example using acceptor coenzyme (redox couple)   NAD+  <-->  NADH* 
  

        Thus : metabolism becomes the stepwise oxidation of foods

  
                           if aerobic - requires oxygen as electron acceptor
     
                           if anaerobic - requires no oxygen (uses other e- acceptors)  

   69.gif (256 bytes)       

 

 

 

 

 

 

 

 

 
  Cell RESPIRATION...   is                    Concept Activity 9.1  - Overview of Cellular Respiration     
                                                                                   
Investigation chapter 9.1  -  How Rate of Respiration is Measured
                                                                          

             1.  oxidation of GLUCOSE --> CO2 + H2O
       &    2.  reduction  O2  to  H2O
     

                     C6H12O6 + 6O2   <---->   6 CO2 + 6 H20    + e- --->    36-38 ATP
                                           
  DG  =  -686 Kc/mole                                263Kc  = 38%

                                called oxidation...  because e- are removed from glucose
                 

                                called reduction...  because e- passed to O2 making water
       &    3.  phosphorylation of ADP  (thus oxidative phosphorylation)          
 70.gif (264 bytes)

 

 

 


 
a more complete definition of cell respiration :
 
    -  series of enzyme rx's (biochemical pathways) in the cytoplasm & mitochondria that,
  
    -  remove e- (oxidation) from covalent bonds of substrates (as glucose), and
  
    -  pass e- to acceptor molecules [coenzymes] such as NAD+ & FAD*
                   which become reduced [ NADH  & FADH2 ]
  
    -  the reduced coenzymes [ NADH & FADH2 ]  pass e- to other acceptors...
                   a series of protein electron carriers called cytochromes,
  
    -  the electron carriers [cytochromes] pass e- to O2   --reduction-->   H2O
  
    -  cytochromes also pump protons [H+]  out of mitochondria into peri-mito space,
  
    -  protons move back into mito thru a special enzyme (ATPase*)  &  make ATP

71.gif (292 bytes)

 

 

 

 

 

         

 
   
the 
Enzyme Pathways* of Cell Respiration...
 
   
 
      Glyco-lysis :  converts   1 glucose (C6) to 2 pyruvate (C3)
           produces :  2 pyruvate,   2 NADH,   &   2 ATP (net)
           occurs in :  cytoplasm  [anaerobic]
           may include :  alcoholic fermentation     =   glucose --> alcohol
                                lactic acid fermentation  =   glucose --> lactic acid
  
Glucose
      KREBS Cycle :  oxidizes :          2 pyruvate  to   CO2  +  H2O
                              produces :         8 NADH,   2 ATP,    2 FADH2
                              releases :          6 CO2  
                              occurs in the mitochondria  [aerobic]
     
      ETC - Electron Transport Chain :
                         passes   e- & H+  from  NADH & FADH2  to  O2  to make H2O
                         generates a proton gradient (chemiosmosis) across the inner mitochondria membranes
  
  &  ATPsynthase :          the enzyme of the inner mitochondrial membrane
 72.gif (228 bytes) end                        that lets  H+  back into mitoplasm & makes ATP directly


     

  

 
                      

 

 

 

 

Glycolysis...                          don't memorize the pathway, but learn the...
           KEY REACTIONS of GLYCOLYSIS...                      
Concept Activity 9.2 - Glycolysis
                   1.  substrate level phosphorylation* [occurs twice in glycolysis]
                   2.  redox reaction   step 6*  involving   NAD+   
                
3.  reactions -->    investment phase*  &  payoff phase*  -  Summary of glycolysis* 
                                                            
Quicktime movie animation of glycolysis
*view for homework 

FATE of NADHneed to regenerate NAD+: mito membranes is impermeable to NADH
        alcoholic fermentation*          "history of wines
        lactic acid fermentation*         also called anaerobic respiration
        shuttles*  malate shuttle        (liver, kidney, heart) =   NADH c --> NADH m 
                       glycerol-P shuttle  (muscle/brain)          =   NADH c --> FADH2m
        Purpose:  to move electrons captured in cytosolic NADH c into mitochondria

Alcohol

  FATES of PYRUVATE   (figure*)                                       Concept Activity 9.5 -  Fermentation
                      if    anaerobic    alcoholic fermentation  &   lactic acid respiration
 77.gif (328 bytes)              if    aerobic        pyruvate dehydrogenase  +  Krebs Cycle

 

 

 

 


  

       
SUMMARY GLYCOLYSIS   figure*

              -  2 ATP to initiate

              -  2 substrate level phosphorylation steps  =  4 ATP gross


                thus Glycolysis makeswhat goes in & come out*
                          2   ATP (net),
                          2   NADH, and
                          2   PYRUVATES

                               remember the role of the ...  Fermentations & Shuttles 

76.gif (316 bytes)

 

 

 

 

 

   
 Heterotrophic Metabolism in Aerobic Organisms...
   
   Krebs Cycle [Sir Hans Krebs]                                      the Fate of Pyruvate* 

    PYRUVATE DEHYDROGENASE Reaction...    
            in mitoplasm (Fig 9.10)*  oxidizes  PYR --> acetyl-CoA
            a multienzyme complex of 60 proteins and 5 coenzymes 
            involves CoASH*    ----->     acetyl coenzyme A          [Fritz Lippman]
            reactions:   1.  decarboxylation (-CO2),  
                              2. reduction of NAD+ 
-->  NADH,
                              3. acylation & synthesis of AcoA
*

                                                                                                                                                                           
    KEY Reactions of KREBS CYCLE                          
            1.   NAD+ is reduced  (NADH)   and   FAD is also reduced (FADH2)
            2.   substrate level phosphorylation occurs  (GTP <--> ATP)
            3.   decarboxylation occurs   [-COOH]
            4.* an acylation reaction via coenzyme-A  (forms Acetyl-coA) 
                                                                                 
                 SUMMARY Reactions:  [Krebs Cycle Quicktime Movie*]    Summary figure    full cycle*
  75.gif (329 bytes)         --> how many actual ATP have we made so far?      Activity 9.3- The Citric Acid (Krebs) Cycle


                                                                                               




                                            

 

     

 

            



 OXIDATIVE PHOSPHORYLATION   &   ELECTRON TRANSFER CHAIN...
                                              
                                                                                                   Concept Activity 9.4 - Electron Transport*
        the coupling of oxidation of substrates (-e) to the phosphorylation of ADP to make ATP
   
µ remember, most of the energy of glucose's bonds is now carried in NADH & FADH2  
                  e- passed from NADH/FADH2  to  O2 via "carrier molecules"*     names*  
        these series of electron carrier proteins occur in 4 membrane subunits  fig 9.16*   
               I)      NADH Reductase,                II)    Succinate Dehydrogenase
               III)  Cytochrome Reductase,         IV)    Cytochrome Oxidase
   
 CHEMIOSMOSIS
  (fig 9.16*)    &     ATP Synthase    (fig 9.14*  &  EM)
           creation of a hydrogen ion gradient (H+)  by  e- flow thru the ETC 
                        -  some e- carriers release protons to outside (into perimitochondrial space)
                        -  H+ diffuse back into mitoplasm thru ATP synthase ---> ATP via a molecular motor*
                        -  ATP synthase animation of mechanism by D. Nicholson*  Boyer hypothesis
                        -  bacteriorhodopsin* provides experimental proof of H+ gradient making ATP
  

                          µ   A rule of thumb for amount of ATP made per e- pair                        
                                    (P/O ratio)
*    -->    NADH3 ATP       FADH22 ATP
74.gif (215 bytes)  
                    john kyrk's animation of mitochondria   &        Biovisions ATPsynthase animation*

   

 

 

 

     
  

 
OVERVIEW of Cell Respiration*...

        How much ATP is made per Glucose* ?     based on 3 ATP per NADH  &  2 ATP per FADH2
                                                                     idealized = 36 to 38 ATP 
     
        What can serve as substrates for aerobic metabolism?*
                            carbohydrates, proteins, lipds... can serve as substrates
     

        Aerobic metabolism intermediates are precursors for other molecules*
  

        How is heterotrophic metabolism regulated?*  
                1.  stiochiometric substrate concentration levels is main controls
                2.  allosteric controls include:  +AMP/ADP stimulates  &    +ATP inhibits
                3.  Key Enzyme :   PHOSPHOFRUCTOKINASE
                                                  feedback inhibition
                                                  allosteric regulation   
74.gif (215 bytes)  

 

 

 

 

 

    
SUMMARY
- Heterotrophic Metabolism - Cell Respiration

    1. Substrates = sugars,   amino acids acids,   fatty acids

    2. Glyco-lysis,  Krebs Cycle,  &  ETC are Universal to all cells

    3. Products = C02, H20, and energy as  NADH,   FADH2, &   ATP

    4. part of process is Anaerobic (-02 ; GLYCO-LYSIS)
                          alcohol & lactate fermentations    (... anaerobic respiration)
                    & part is  Aerobic  (+02glycolysis &   Krebs Cycle)

    5. Reactions include:
                 oxidation, reduction, decarboxylation, phosphorylation,
                            acylation  &   hydrolysis  (or dephosphorylation)
72.gif (228 bytes)

 

 

 

 

 

    
    6. Energy capture is via   electron transfers   &   proton pumps  [ATP synthase*]

    7. Regulation is by:
                feedback inhibition   &   allosteric modulation 
                of key enzyme:  phosphofructo-kinase

    8. Intracellular compartmentation:
                glycolysis is in the cytoplasm
                Krebs Cycle is mostly in the mitoplasm of mitochondria
                ETC is in the cristae membranes of mitochondria

    9. is central KEY* to all Metabolic pathways in Cells
                                   
IUBMB-Nicholson Metabolic Pathways Chart

    73.gif (208 bytes)        next lecture* - photosynthesis                    a paradigmKey Concepts*

 

 

 

 

 

 

 If you have comments or suggestions, email me at  cmallery@miami.edu

          University of Miami Home Page  |  Biology Home Page
          Dr. Mallery's Home Page            |  On-Line Testing Center.
          copyright c2007,
          Charles Mallery, Department of Biology, University of Miami, Coral Gables, FL 33124

          Last Update -June 04, 2008

 

 


 

 

-   Individual reaction steps of glycolysis