18.5 Anaerobic Respiration Flashcards
When is anaerobic respiration used?
In the absence of O2
When O2 can’t be supplied fast enough to respiring cells
When there’s lack of oxygen, what does anaerobic respiration act as?
An emergency measure to keep vital processes functioning
What are the 3 categories of organisms based on their oxygen needs?
Obligate anaerobes
Facultative anaerobes
Obligate aerobes
What is the O2 dependency of obligate anaerobes? What type of organism are most obligate anaerobes?
Can’t survive in presence of O2
• Almost all are prokaryotes, but there are some fungi
What are facultative anaerobes? Give an example of this organism
Synthesise ATP by aerobic respiration if O2 is present, but can switch to anaerobic in absence of oxygen
e.g. yeast
What are obligate aerobes? Give an example of this organism.
Only synthesise ATP in presence of oxygen
e.g. mammals
Why can muscle cells of mammals be described as facultative anaerobes? Why aren’t they fully facultative anaerobes?
The cells can supplement ATP by anerobic respiration if O2 conc.s are low. However, eventually O2 is required.
Why are mammals as a whole obligate anaerobes?
When anaerobic respiration is used during low oxygen periods, compounds are produced which have to be broken down when O2 is available again
What is fermentation?
When complex organic compounds are broken down into simpler inorganic compounds w/o use of oxygen or ETC
What type of respiration occurs in fermentation?
Anaerobic
Why does fermentation produce less ATP than aerobic respiration?
Organic compounds (e.g. glucose) aren’t fully broken down
Where does alcoholic fermentation occur?
In yeast and some plant roots
What are the end products of fermentation?
Ethanol (alcohol) and CO2
Where does lactate fermentation occur?
Animal cells
What is the end product of lactate fermentation?
Lactate
What happens when oxygen is no longer available to act as the final electron acceptor at the end of the ETC (in oxidative phosphorylation)?
- Flow of electrons stops - so synthesis of ATP by chemiosmosis stops
- Reduced NAD+FAD are no longer oxidised bc no flow of electrons
• This means NAD + FAD no longer regenerated in Krebs cycle, so decarboxylation and oxidation of pyruvate + in Krebs cycle halts, as there are no coenzymes to accept the H removed
How does lactate fermentation work?
- Pyruvate acts as H acceptor, taking H from reduced NAD , catalysed by lactase dehydrogenase
- Pyruvate is converted into lactate and NAD is regenerated
- This regenerated NAD can be used prevent glycolysis stopping, so small amount of ATP are always synthesised
What is the name of the enzyme which catalyses lactate fermentation?
Lactate dehydrogenase
What is anaerobic respiration supported by?
ATP supplied by aerobic respiration
What’s happening with aerobic respiration during exercise?
ATP from aerobic respiration is still being produced as fast as oxygen can be delivered into the body
What happens to lactic acid once the body gets more O2?
The lactic acid is converted into glucose in the liver. O2 is needed for the conversion of lactate -> glucose
What are the 2 reasons for why lactate fermentation can’t occur endlessly?
- Reduced quantity of ATP produced wouldn’t be enough to maintain vital processes for extended periods of time
- Accumulation of lactic acid decreases pH, leading to denaturing of proteins - respiratory enzymes and muscle filaments are made from proteins and won’t function at low pH
What’s the difference between lactate fermentation and alcoholic fermentation in terms of reactions?
Lactate fermentation is reversible. Alcoholic fermentation is irreversible.
What happens during alcoholic fermentation?
- Pyruvate converted into ethanal, catalysed by pyruvate decarboxylase
- Ethanal accepts a H from reduced NAD and becomes ethanol
