8/8/2019 Fermentation and Anaerobic Respiration

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Fermentation and Anaerobic Respiration. 

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Fermentation: If oxygen is absent, many cells are still able to use glycolysis to produce ATP.Two ways this can be done are through fermentation and anaerobic respiration. Fermentation isthe process by which the electrons and hydrogen ions from the NADH produced by glycolysis

are donated to another organic molecule.

The point of fermentation 

The reason this is done is to produce

 NAD+ which in tern is needed to keepglycolysis going. Remember, that unless

the cell has some sort of electron

transport system, the NADH is notusable. At the same time NAD+ isneeded for glycolysis and its much less

expensive in terms of energy for the cellto simply take the NADH that would

normally go to the mitochondrion anduse it to regenerate the NAD+. This is

shown in the figure for ethanolfermentation in yeast.

 Notice that the NADH produced by

glycolysis donates it's hydrogen ionsand electrons that in aerobic respiration

would have ended up powering electron transport phosphorylation.

Other fermentation pathways 

There are a number of fermentation pathways that different cells use. Yeast cells produce ethyl

alcohol by fermentation. Certain cells of our body, namely muscle cells, use lactic acidfermentation, while depending on the organism some of the other products of fermentation

include acetic acid, formic acid, acetone and isopropyl alcohol.

Fermentation and running 

In our bodies certain muscle cells, called fast twitch muscles, have less capability for storing andusing oxygen than other muscles. When you run and these muscles run short of oxygen, the fast

twitch muscles begin using lactic acid fermentation. This allows the muscle to continue tofunction by producing ATP by glycolysis.

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The muscles get enough ATP for quick spurts or shall we say sprints, but quickly becomefatigued as their stores of glycogen are used up. Eventually you cramp. This is in part because

the muscles lack sufficient ATP to continue contracting. Also, lactic acid builds up and must bemetabolized by the liver. Runners who sprint actually have more muscle cells specialized for 

lactic acid fermentation than do long distance runners.

White meat and dark meat 

If you want to see what these muscles are like, when you eat chicken or turkey the white meat isfast twitch muscle. The dark meat is what is called slow twitch muscle. This meat is dark 

 because it contains an oxygen holding protein called myoglobin. Note that the slow twitchmuscles tend to be wing and leg muscles where long term endurance is required. The fast twitch

muscles tend to be more common in the breast where quick response but not necessarilyendurance is needed. Also, wild animals tend to have more slow twitch muscle than their 

domestic counterparts.

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 pgd revised 02/20/00