Anaerobic Respiration

> Oxygen is needed to convert the hydrogen atoms produced in glycolysis and the Krebs Cycle to water and drive the production of ATP.

> In the absence of oxygen, the Krebs cycle and ETC cannot take place. This leaves only the anaerobic process of glycolysis as a potential source of ATP.

> For glycolysis to continue, its products need to be continually removed, in particular the hydrogen from the reduced NAD must be released in order to regenerate NAD. Without this, the short supply of NAD will all be converted to reduced NAD, leaving no NAD to take up hydrogen newly produced from glycolysis.

> Glycolysis will then stop

> Replenishing NAD is achieved by the pyruvate molecule from glycolysis accepting hydrogen from reduced NAD.

> In eukaryotic cells, only 2 types of anaerobic respiration regularly occur:

    > Pyruvate converted to ethanol & CO2 in plants & microorganisms

    > Pyruvate converted to lactate in animals

> Occurs in organisms such as bacteria & fungi & come cells of higher plants

> Pyruvate molecule produced at the end of glycolysis loses a molecule of CO2 & accepts hydrogen from reduced NAD to produce ethanol:

                                         Pyruvate + reduced NAD --> ethanol + CO2 + NAD

> Means of overcoming temporary shortage of oxygen

> Occurs most commonly in muscles as a result of strenuous exercise (oxygen may be used up more rapidly than it can be supplied = OXYGEN DEBT)

> The muscles continue to work despite lack of oxygen;

     > Glycolysis would usually cease as reduced NAD accumulates

     > This reduced NAD needs to be removed, so each pyruvate molecule produced accepts 2 H atoms from reduced NAD produced in glycolysis to form lactate:

                                    Pyruvate + reduced NAD --> lactate + NAD

> At some point the lactate produced needs to be oxidised back to pyruvate, which can be further oxidised to release energy or converted to glycogen. Happens when oxygen is available again.

Energy from cellular respiration is derived in 2 ways:

   > Substrate-level phosphorylation in glycolysis & the Krebs cycle. Direct linking of inorganic phosphate to ADP to produce ATP.

   > Oxidative phosphorylation in the ETC. Indirect linking of inorganic phosphate to ADP to produce ATP, using the H atoms from glycolysis & Krebs Cycle that are carried on NAD & FAD. Cells produce most of their ATP in this way.

> In anaerobic repiration, pyruvate is converted to ethanol / lactate. Not available for Krebs cycle. Krebs cycle & ETC cannot take place.

> The only ATP that can be produced is by glycolysis > very small amount!