cellular respiration: pyruvate oxidation and citric acid/krebs cycle

pyruvate oxidation overview

• linking stage between glycolysis (anaerobic) and citric acid/krebs (aerobic)

• oxygen required

• one pyruvate molecule turned into one acetyl group

• acetyl group attaches to coenzyme A (carrier molecule) to be acetyl CoA, used in krebs cycle

• NAD⁺ reduced to NADH

• occurs in intermembrane space to matrix

• stage 2 of cellular respiration

fates of pyruvate

• there are many pathways that pyruvate can take

• very common molecule

• anaerobic yeast: pyruvate decarboxylase, makes alcohol

• aerobic yeast: makes acetyl coA, energy or fat

• other anaerobic substances: makes lactate (sore muscles)

• other aerobic: oxidative decarboxylation of pyruvate into acetyl coA, energy or fat

pyruvate to acetyl-coA formula

2 pyruvate + 2NAD⁺ + 2 CoA → 2 acetyl-CoA + 2 NADH + 2H⁺ + 2 CO₂

krebs cycle overview

• also called citric acid cycle

• stage 3 of cellular respiration

• aerobic

• completes breakdown of glucose

• consists of 8 enzyme catalyzed reactions

• uss acetyl coA to produce energy in the form of NADH, FADH₂, ATP and releases CO₂

• Hydrogen ions and electrons are stripped and loaded onto NAD⁺ and FAD to produce NADH and FADH₂

• 2 cycles per one molecule of glucose

krebs cycle steps

• every step includes an enzyme catalyzed reaction that forms a new molecule

• enrgy released from ^ reaction used to reduce NAD⁺ to NADH

• 2 carbons acetyl coA bond with oxaloacetate form citrate (6 carbon)

• citrate loses carbon and produces CO₂ + NADH, forms 5 carbon molecule

• loses another carbon, prodces CO₂ and NADH, forms 4 carbon molecules

• GDP, similar to adp, forms gtp, = to atp

• FAD reduced to FADH₂, electron carrier similar to NADH

• NAD+ reduced to NADH

• forms oxaloacetate, 4 carbon molecule

• acety coA completly changed to CO₂ and H₂O

end result of krebs cycle

• per 1 molecule of glucose

• two full turns

• 2 atp

• 6 NADH

• 2 FADH₂

• FADH₂ and NADH electron carriers will make abundance of ATP for ETC

what molecule is this?

pyruvate

what molecule is this?

acetyl coA

label

• pyruvate oxidation

• 1: carbon dioxide (1a) is released 

• 2: NAD⁺ (2a) is reduced to NADH (2b) and hydrogen ions are produced (3c)

• 3: coenzyme A (3a) is added 

• 4: cytosol

• 5: pyruvate

• 6: transport protein

• 7: mitochondrion

• 8: acetyl coA

label

• krebs cycle

• 1 = acetyl coA

• 2 = citrate

• 3= NADH

• 4 = CO2

• 5 = NADH

• 6 = CO2

• 7 = GTP, equivalent to ATP

• 8 = FADH₂, similar to NADH

• 9 = NADH

• 10 = oxaloacetate