Energy yielding schemes

Aerobic respiration

C₆H₁₂O₆ + 6O₂ ==> 6CO₂ + 6H₂O + energy (ATP +heat)

 

Organic compounds + oxygen ==> carbon dioxide + water + energy

Glycolysis

Tricarboxylic acid cycle (Krebs cycle)

Electron transport system (ETS)

-----------------------------------------------------------------------

Glycolysis (Embden-Meyerhof-Parnas pathway)

Oxidation or breakdown of glucose into two molecules of pyruvic acid

Occurs in the cytoplasm of all cells.

It is the most commonly used sequence of reactions for the conversion of glucose into pyruvate

Produces 2 ATP's, 2 NADH's and 2 H₂0 molecules

Does not require oxygen

-------------------------------------------------------------------------------

Tricarboxylic acid cycle (TCA) or Krebs cycle

 

Discovered by Egleston and Krebs

Occurs in the cytoplasm of procaryotes and in mitochondria of eucaryotes

Process the final 2-C molecule (Acetyl-CoA) coming from pyruvic acid obtained from the degration of glucose (6C) via glycolysis

Cycle has 8 steps, reduces 2 FAD and 8 NAD’s, releases 2 CO₂ and produces 2 ATP’s by substrate level phosphorylation
Fig. 8.23

 

 

---------------------------------------------------------------------------

Electron transport system (ETS)

 

Occurs in cell membrane of procaryotes and in mitochondria of eucaryotes

Made of a chain of special redox carriers that received electrons from reduced carriers

Produces 34 ATP's and 6 H₂0 molecules

In aerobic metabolism, oxygen is the final electron acceptor and combines with H ions (protons) to form water.

In anaerobic metabolism, other ions may act as final electron acceptors

 

--------------------------------------------------------------------------

Chemiosmotic theory

Explains the origin and maintenance of electro-potential gradients across a membrane that leads to ATP synthesis, by ATP synthase (oxidative level phosphorylation)
(Figs. 8.22, 8.23 and 8.24)

The energy obtained is used to regenerate up to 38 ATP (this number may vary among microbes) for each glucose molecule catabolized (Table 8.4)

-------------------------------------------------------------------------------
Anaerobic respiration

Fermentation

The anaerobic enzymatic conversion of pyruvic acid to organic acid or alcohol or other organic compounds producing energy in the form of ATP

Incomplete oxidation of glucose or other carbohydrates in the absence of O₂

Organic molecules can serve as final electron acceptors

Inorganic salts can also serve as electron acceptor: NO_3^-, SO₄^-2, CO₂, ATP, organic cids, H₂S, CH₄

2 ATP’s maximum per glucose molecule

25% of the energy of glucose transferred to ATP

-----------------------------------------------------------------------------

Occurs in facultatives anaerobes, aerotolerant, strict anaerobes

Allows independence from O₂ and allows colonization of anaerobic environments

Enables microorganisms with a versatile metabolism to adapt to variations in the availability of oxygen

Bacteria that digest cellulose in the rumen of cattle are largely fermentative providing the animal with glucose, a source of energy

The phosphogluconate pathway is an alternative anaerobic pathway

-----------------------------------------------------------------------------
Fermentor

A large tank used in industrial microbiology to grow mass quantities of microbes that can synthesize desired products

These devices are equipped with means to stir, monitor and harvest products such as a variety of organic acids and alcohols in very large quantities

---------------------------------------------------------------------------------
Textbook: Foundations in Microbiology. K.Park Talaro. 6th edition. McGraw Hill.

Remember to read your textbook, study tables, graphs and illustrations.
Develop a strategy to administer your time so that when exams come you do not have to cram.
Attend lectures and ask questions.

Lecture notes are posted BEFORE lecture is given thereafter they will be removed.