Substrate-level phosphorylation

 

review oxidation

          typical redox reaction

 

   substrate - level phosphorylation (SLP)

          - a molecule of ADP acts as a substrate on an enzyme

          - phosphate donor sits on the enzyme as well

          - enzyme catalyzes the transfer of a phosphate group from the donor to ADP

 

   When the reaction is completed, the intermediate (minus its Pi) and ATP

   are released from the active site

 

                 intermediate - P_i + ADP ® intermediate + ATP

                    reactants                             products

 

Step nine

 

Phosphoenolpyruvate -> Pyruvate

 

  DG^0' = -14 kcal/mole + 7.5 kcal/mole = -6.5 kcal/mol

  Enzyme: Pyruvate Kinase

 

 

   Aerobic respiration

overview1

overview 2

 

   In eukaryotic cells, in the presence of oxygen, pyruvate diffuses into the

   mitochondrion to undergo further oxidation.  The pyruvate is converted

   to three molecules of carbon dioxide which will diffuse from the cell as a

   waste product.  Remember where things happen, in what sequence, the

   ATP yield, and the purpose of the reaction or pathway.

 

   The conversion of pyruvate

 

NB: for each glucose entering the cell TWO pyruvate are formed in glycolysis

 

o       pyruvate is converted to acetyl CoA in the mitochondrial matrix

o       CoA is a coenzyme that feeds 2C fragments into the next step

o       carbon dioxide is released

o       NADH is formed

o       treat this step separately from the next stage

 

   Pyruvate + CoA + NAD⁺ ®acetyl CoA + carbon dioxide + NADH

               reactants                                             products

 

 

   Krebs cycle

overview

 

o       acetyl CoA donates the acetyl (2C) fragment to  the first enzyme of the Krebs cycle

o       CoA is then ready to pick up  more 2C fragments from pyruvate or other fuel molecules

o        each turn of the cycle spins off 2 carbon dioxide, 3 NADH, 1 FADH₂  (another high-energy

     electron carrier) and 1 ATP (SLP)

o       carbon dioxide is released from the cell as a waste product

o       at the end of this cycle, all that remains are the electron carriers

 

DO NOT FORGET THAT ATP IS FORMED IN THE KREBS CYCLE THROUGH SLP

 

In class: what you need to know about the Krebs cycle

 

 

   Electron transfer chain

ETC in mitochondrion (animation)

ATP synthesis

ATP synthesis

 

·          a series of redox reactions where the electron carriers are oxidized and oxygen is reduced

·          electrons donated to the ETC lose energy at each transfer

·          ETC is situated in the inner membrane of the mitochondrion

·          as the electrons travel, protons (H⁺) are pumped from the matrix into the intermembrane space

 

   The inner membrane is impermeable to ions, so the protons accumulate in this space

creating a concentration gradient and an electrochemical gradient.

 

There is only one escape valve: ATP synthase.