Monday WK 6

Aerobic Cellular Respiration

2nd Stage: Formation of Acetyl Coenzyme A (COA)

Reactants:

  • 2 Pyruvic acid
  • 2 coenzyme A

Products

  • 2 CO2
  • 2 NADH
  • 2 Acetyl COA

3rd Stage: Krebs Cycle

Reactants

  • 2 Acetyl COA

Products

(Goes through Krebs cycle twice)

  • 3 NADH    x2 = 6 NADH
  • 2 CO2        x2 = 4 CO2
  • 1 ATP         x2 = 2 ATP
  • 1 FADH2   x2 = 2 FADH2

◊ ATP is made by substrate-level phosphorylation during Krebs cycle.

◊ NAD+ (oxidized) can take on H+ and carry them becoming NADH (reduced)

4th Stage: Electron Transport Chain & Chemiosmosis

Reactants

  • 10 NADH
  • 2 FADH2
  • 6O2

Products

  • 34 ATP
  • 6 H2O
  • 10 NAD+
  • 2 FAD

◊ Chemiosmosis – Chemical osmosis. Flow of electrons back down their gradient through ATP synthase. 

◊ (ETC) – Electron Transport Chain – Series of molecules (embedded in cell membranes) that transport/carry electrons through redox RXNs, releasing energy for making ATP. Final electron acceptor is Oxygen. (O, not O2)

Process: the electron transport chain is embedded in the cytoplasmic membrane of bacterial cells or the inner membrane of mitochandria in eukaryotes. The electrons are passes through molecules in Redox RXNs, being pulled towards the oxygen that has the highest electronegativity, where is will finally be accepted. During this process H+ (which are taken from the FADH2 & NADH) are pushed through the membrane and began to buildup against their gradient, the H+ are filtered out through ATP synthase “portals” through the membrane creating ATP (this process is the Chemiosmosis)  in this RXN:          

ADP + P → ATP

3 Types of Electron Carriers in ETC:

  1. Flavoproteins – ex. flavin mononucleotides (FMN)
  2. Cytochromes (contain iron) – ex. Cytochrome C
  3. Ubiquinones – Coenzyme Q (COQ)

Summary table:

Glycolysis:                    4 ATP – 2 ATP used = 2 ATP          2 NADH

COA & KREBS:           2 ATP – 2 ATP used for eukaryotes only = 0 ATP             8 NADH            2 FADH

ETC:                              34 ATP

Net For Prokaryotes = 38 ATP

Net For Eukaryotes = 36 ATP. Note: Eukaryotes glycolysis process (stage 1) takes place in the cytosol, 2 ATP are expended to move the RXN through the membrane.

 

Alternate Pathways for Glycolysis

Pentose Phosphate Pathway

  • produces pentose sugars (for nucleotide synthesis)

Entner-Dourodoff Pathway

  • Glucose catabolized to pyruvate but w/ different enzymes
  • Occurs in a few prokaryotes (but not eukaryotes)
  • ex. Pseudomonas aeruginosa & Enterococcus faecalis

Carbohydrate Catabolism: Fermentation

  • Uses an organic molecule as final electron acceptor (NAD+ → NADH)
  • Does not require O2
  • Produces 2 ATP per glucose molecule
  • Other Products: Various acids such as lactic acid; gases such as CO2; alcohols

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