01.08 Cellular Energy Conversion

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  1. Cellular Respiration- a controlled set of enzymatic reactions that convert glucose into ATP
    1. Aerobic Respiration- occurs in the presence of oxygen (the final electron acceptor) Most efficent 1 gluose yields 36-38 ATP
      1. 5 main Events
        1. Glycolysis- oxidation of glucose into 2 pyruvates (occurs in cytoplasm) and reduction of NAD+ to NADH
        2. Link Reaction- combines pyruvates with CoEnzymeA (occurs across mitochondrial membrane) to make Acetyl CoA which enters the Krebs Cycle.
        3. Beta Oxidation-when fatty acids that enter across the mitochondrial membrane are converted in Acetyl CoA which also can enter the Krebs Cycle.
        4. Krebs Cycle- Each Acetyl CoA through a series of enzymatic reactions produces 1 ATP, 3 NADH, 1 FADH2 for a total of 2 ATO, 6 NADH and 2 FADH2
        5. Oxidative Phosphorylation- The energy molecules produced from the above products fuel the flow electrons across the ETC which builds up an [H+] gradient and with oxygen as the final electron acceptor this electron flow produces ATP.
    2. Anaerobic Respiration- in the absence of oxygen, cells can usually regenerate NAD+ from NADH through the use of an organic molecule using the prcess of fermentation.
      1. Two tyoes of fermentation
        1. Alcoholic fermentation: Pyruvic acid → CO2 + acetaldehyde + NADH → ethanol + NAD
        2. Lactic Acid Fermentation: Pyruvic acid + NADH ↔ lactic acid + NAD+


Hold on tight today as we discuss the process of cellular respiration!

Respiration is not just physiological breathing… its the process of taking that oxygen we breathe and allowing our cells to do a fantastic job of converting sugar into ATP.

So cellular respiration literally strips glucose of its energy worth, just as car thieves steal older model cars to strip it of its parts for resale. Both hold a lot of value/energy and can be released of such value over time.

So we will start with cells doing this when there is oxygen on board. BTW the most efficient way. And this image shows an overview of the main steps. Glycolysis, a hidden link, the Krebs Cycle and the ETC (which is also oxidative phosphorylation.)

So here we begin with the cell splitting glucose (glycolysis). It Occurs in Cytoplasm , there’s no use of oxygen, When it splits glucose it makes 2 Pyruvates, 2 NADH -used at the end and nets 2 ATP-used at the end. I like to think of NAD+ as an electron taxi…. and glycolysis fills it!

Next we have the hidden (a go-between reaction) link that occurs on the outer mitochondrial membrane and basically modifies the 2 pyruvates into Acetyl CoA….which is needed in the next step.

Further in the mitochondria (matrix) those acetyl CoA are gonna be used to drive the Krebs cycle. This will give us 2 ATP, 6 full taxis (NADH), and  2 FAD2 (another electron taxi).

And finally, those taxis shuttle those electrons stripped from glucose to the inner membrane where the will flow across the ETC and pump H+ ions in order to drive production of ATP. Those electrons can keep on coming as oxygen keeps accepting them and the electron flow keeps the ATP factory flowing.  1 sugar can give a cell up to 38 ATP!!!

In contrast…… a cell minus oxygen quite frankly stinks at making ATP… but it can be done. Glycolysis can remain at work as long as fermentation kicks in. With either (alcoholic or lactic acid) basically your keeping the glycolysis in action and the rest doesn’t occur. Yeast cells do this well and make carbon dioxide gas and ethanol as byproducts. An animal cell does this (not sustainably) and this results in lactic acid which causes our muscles to fatigue.

In summary, cell respiration converts glucose into ATP. Glycolysis splits sugar into 2 pyruvates, the link reaction modifies those pyruvates so they can spin the Krebs cycle and ultimately what was done was energy was methodically released from glucose in order to make ATP.

And when cells run out of oxygen… there are options to keep only glycolysis running… but your 1) not gonna make a lot of ATP, 2) if your a yeast cell your gonna burp a lot of CO2 and possibly get an ethanol hangover and 30 if your an animal cell your muscles are gonna feel the burn thanks to lactic acid fermentation.

Thank you for allowing us to share with you a fun and insightful look at how cells convert energy. Now go out and be your best self today and happy nursing!