Stimulation and Inhibition

• cells control cellular respiration by feedback inhibition of ATP or citrate on the phosphofructokinase (PFK) enzyme in glycolysis and pyruvate dehydrogenase complex (PDC) when it gets oxidized

• PFK can be stimulated by ADP when ATP levels are low

• PDC is inhibited by acetyl-CoA, NADH, and ATP while pyruvate & ADP activate it

Anaerobic Pathways

• the electron transport chain & chemiosmosis are able to work because of oxygen as a final electron acceptor

• still 2 ways for eukaryotes to make ATP (though they’re less effective)

Fermentation

• uses an organic molecule as the final electron acceptor (instead of oxygen)

• not considered respiration

• even without oxygen, glycolysis can have a net gain of 2 ATP → just need a way to oxidize NADH back to NAD+

• 2 types: alcohol & lactate fermentation

• depending on the organism, this can be a primary/secondary pathway

Alcohol Fermentation

• ethanol fermentation

• done by bacteria & yeasts

• normal glycolysis followed by decarboxylation of pyruvate into acetaldehyde

• acetaldehyde then oxidizes NADH back into NAD+ while being converted into ethanol

• only 2 ATP produced

Lactate Fermentation

• supplementary system in eukaryotes occurs in our muscles

  • due to not getting enough oxygen to produce sufficient ATP to meet our demands

• excess pyruvate is converted into lactate through the oxidation of NADH to NAD+

• lactate is transferred to the liver where it is converted back into pyruvate & then into glucose

• only 2 ATP produced

Anaerobic Respiration

• many prokaryotes can use SO₄⁻², NO₃⁻⁻ and Fe³⁺ as electron acceptors in their electron transport chains in order to live in environments without oxygen

Excess Sugar Molecules

• if ATP is not needed and glycolysis is inhibited the sugar molecules can be stored as glycogen or fats

Glucose Alternatives

• cellular respiration can run on proteins & fat as well as carbohydrates

• different enzymes break these molecules down so they can enter the process at different places

• proteins need to have the nitrogen removed before they can be used for energy - this is called deamination

• fats are broken into glycerol & fatty acids as a first step

Protein Deamination

• each amino acid needs a different enzyme to remove the amino group

• ammonia is a waste product that gets converted to urea and excreted in urine

• the Nitrogen needs to be dealt with in breaking the protein down

Amino Acids in Respiration

• different amino acids enter the respiration process at different points once the amino group is removed

• the place where the amino acid enters depends on how many carbons it has