Rate my answer regarding fermentation.

[1MileCrash]

I have been given a bonus question prior to the test.

Compare the end products and total energy yield for glycolysis and respiration with fermentation in muscle cells. What problem does fermentation solve? What problem does fermentation create? What is oxygen debt?

Glycolysis & Respiration differs from Fermentation in many ways. A unique feature of mammalian muscle cells when compared to other types of cells is the ability to switch from Glycolysis & Respiration to Fermentation when circumstances require. Muscle cells will only switch to fermentation when oxygen is scarce because respiration yields much more energy than fermentation. Respiration yields 36 (theoretical) net ATP per glucose molecule, much greater than the yield of fermentation, which is 2 net ATP per glucose molecule.

Glycolysis reduces NAD+ to NADH, but due to the limited amount of NAD+ within the cell, NADH must be "recycled" by being oxidized back into NAD+, which is normally done via an electron transport chain in cellular respiration. However, this process can only work in the presence of oxygen because it is the final electron acceptor of the ETS.

During vigorous activity, the circulatory system cannot keep up with the cellular demands for oxygen. This becomes a problem for glycolysis, as the NADH can no longer be oxidized back into NAD+ through respiration.

Fermentation solves this problem of oxygen deficiency and allows glycolysis to continue. Rather than NADH being reduced by the ETS, NADH and the Pyruvate created by the initial splitting of glucose enter a Redox reaction. The oxidation of NADH recycles it into NAD+, allowing glycolysis to continue; the reduction of pyruvate yields an organic acid known as lactic acid.

However, the problem with fermentation is the accumulation of lactic acid, which interferes with muscle function. After vigorous activity has stopped, the accumulated lactic acid is catabolized into CO2 and water. This process also requires additional oxygen. The amount of additional oxygen needed to catabolize the accumulated lactic acid is termed the oxygen debt.

 

[epenguin]

I know what you mean and I could see nothing factually wrong. My only criticism/opinion would be stylistic - that it could only be understood by someone who knows what you mean.

For a good communication you could afford to expand this by as much as half again - try to get into mind of someone who does not know what you are talking about. Try to condense the essentials of this succinctly in your own mind with a time limit, I realize it could take forever if you let it.

E.g. you are asked the products - I wonder if it would be a good idea for a reader to say these at the start with some overall equations, instead as part of the consequences of your explanations. It is excellent to know everything as a whole; the trouble is when you explain it it has to become a sequence. By the way you did not answer the question what is product of fermentation? (showing off, as well as alcoholic fermentation there is also lactic fermentation - quite an industry!)

Optionally a fact related to lactate and exercise I only learned a short time ago is here https://www.physicsforums.com/showpost.php?p=3189582&postcount=5 if you choose to show off - but then make sure you can answer if you are asked questions that would reveal whether you have read the article in question!

 

[1MileCrash]

Thank you, I need all the help I can get. Last exam I was asked the origin of eukaryotic cells ( by prokaryote symbiosis theory ) and I thought my answer was superb, I put a lot into it and got 9 points out of 10.

 

[bobze]

Pretty good. I'd add a couple of things though. You may want to talk about the speed that ATP becomes available through each cycle. Its not necssarily the lack of oxygen that fuels the lactate cycle, rather sometimes the energy demand placed upon muscle cells.

Doing substrate level phosphorylation via glycolysis generates ATP much faster for the cell, than does doing oxidative phosphorylation via the cell's mitochondria. Its also why muscle cells keep a nice supply of creatine phosphate (phosphocreatine) around--To quickly generate energy when needed (like a fight or flight response).

I'd also add how the lactic acid is dealt with (its sent to the liver, where it gets converted, via gluconeogenesis, to glucose for the muscles to use to restore energy balance--They go into a sort of "energy debt" during vigorous exercise).

You may also want to add in something short about how glucose is stored in muscle (glycogen) and how that becomes available for glycolysis during activity and then if you really want to show off, put in some quips about how these processes can go wrong with a disease example (like glycogen storage diseases, McArdle's is a good one to illustrate the differences between oxidative and non-oxidative energy production).

Edit: Or maybe that is way to in depth for the level of class you are in :P. Can you tell us what class this is for the general level you are studying these topics?

 

[1MileCrash]

Biology 155, and lab. The very first biology that biology majors take. I'm a physics major but it's required.

I didn't get to read your post before taking the exam though. I don't believe in holding back because the class is introductory, right is right.

Thanks.