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Anaerobic Respiration in Humans

Could anyone kindly explain the process of anaerobic respiration in humans, please? I'm guessing only a simplified knowledge of the process is required, however pyruvic acid and lactic acid both have been mentioned by the teacher.

This is what I have managed to grasp, but I'm not really sure about it, so please correct me if I'm wrong!
Okay, so muscles produce pyruvic acid when they respire anaerobically. So the equation would be:
Glucose ----> Pyruvic acid + carbon dioxide + energy
Somehow this acid is converted to lactic acid (how, why and where does this happen?) ... then what happens to this lactic acid?

Any help would be very much appreciated! Word equations would be particularly useful, too!

Many thanks!

Reply 1

Keira Larkin

Original post by PepperPeppermint

So during aerobic respiration, glucose is converted into pyruvic acid via many steps. Then it would convert this pyruvic acid into acetyl coenzyme A. Acetyl coenzyme A would be converted to something else in a series of many complex steps that I won't go into.

During anaerobic respiration, the cell cannot convert pyruvic acid into acetyl coenzyme A because of the lack of oxygen. So it instead converts pyruvic acid into lactic acid using lactate dehydrogenase. The equation you gave seems to indicate that carbon dioxide is released but this is not the case. I would suggest you use this word equation instead:

Glucose --> Lactic acid

Are you doing your GCSE's? If so then you probably don't need all this detail and the equation I've written above will suffice. Also, respiration in yeast is different from respiration in mammalian cells.

Reply 2

username2888406

I'm doing the IGCSE Human Biology so what I need to know for the syllabus may differ for you, so keep that in mind. We need to know the word and chemical equation for anaerobic respiration.

Glucose --> Lactic acid (+ some energy)
C6 H12 O6 --> 2 molecules of C3 H6 O3 (+ some ATP)

Anaerobic respiration is less efficient than aerobic respiration, for every glucose molecule: Anaerobic = 2 molecules of ATP, Aerobic = up to 38 molecules of ATP. ATP is the form or currency of energy that is useable by cells.

Lactic acid builds up in the muscles during anaerobic respiration causing pain meaning this type of respiration can only be sustained for a short period, like when you're sprinting. Oxygen is needed to oxidise or break down the lactic acid that remains in the muscles. The amount of oxygen needed to break down the lactic acid so that the body returns to its original state is known as oxygen debt. This is why you breathe heavily after intensive exercise, the body is taking in lots of oxygen to oxidise the lactic acid. For our syllabus we don't need to know how this oxidisation occurs.

This video goes into detail on cellular respiration, but I don't think you need to know all this at GCSE level, we don't for our syllabus: https://youtu.be/00jbG_cfGuQ

Reply 3

HateOCR

Pyruvate ——(lactate dehydrogenase)——> lactate

NADH2->NAD

Reply 4

PepperPeppermint

Original post by Keira Larkin

Thank you

Yes, I am currently doing what is equivalent to the GCSEs (I'm not from the UK). Our syllabus is very similar to the biology GCSE syllabus, so I'm guessing that if little detail is required for the GCSE, then little detail is what I need to know.

As regards *aerobic* respiration, we didn't even mention pyruvic acid. The equation we were given was this one:
C6H12O6 + 6 O2 ---> 6 CO2 + 6 H2O + 2830kJ of energy (ATP)

Then, when we learnt about *anaerobic* respiration, pyruvic acid seemed to come out of nowhere. I guess that's what confused me.

Might I ask what happens to the lactic acid produced, please?

Thank you for your help, much appreciated :smile:

Reply 5

macpatgh-Sheldon

The lactic acid, as mentioned by one member above, accumulates in the muscles during the period of oxygen debt. When oxygen supply is sufficient again (usually after stopping the exercise), the lactic acid itself is oxidised, and because it contains carbon and hydrogen, the end products are H2O and CO2 [as with aerobic respiration], and these are excreted by exhalation in the lungs, where they diffuse from the blood [taken to the lungs in the pulmonary arteries] into the alveoli, whence they are breathed out.

M

Reply 6

Keira Larkin

Original post by PepperPeppermint

Thank you

Several different things can happen to the lactic acid:

The liver can convert it into CO2 and H2O which macpatelgh has said
Or it can be converted back into pyruvic acid. Then this pyruvic acid can either be converted to acetyl coenzyme A (as I described earlier) or to glycogen.

https://www.livestrong.com/article/552457-can-you-stop-the-production-of-lactic-acid/

The webpage that I have linked explains what I've written in more detail.