Lecture 3a:Cellular Respiration
Lecture 3a:Cellular Respiration
Cellular Respiration
This is the reason you breathe
How cells make ATP from carbohydrates
Essentially the reverse of photosynthesis
Helper molecules
Coenzymes: nonprotein helpers that move electrons and H around
NAD+ and FAD+ become NADH and FADH
4 PhasesGlycolysis: Occurs in cytoplasm
Produces 2 ATP and NADH
Breaks glucose in half into 2 pyruvate
Prep reaction: Occurs in matrix
Produces NADH
Breaks pyruvate into 2-carbon acetyl group
Releases CO2
4 PhasesCitric acid cycle: occurs in matrix
Produces more NADH and FADH2
Releases CO2
Produces 2 ATP
Electron transport chain: Occurs in crista
NADH and FADH2 release electrons
Energy released
Produces water
Glycolysis
Occurs outside the mitochondria
Uses 2 ATP, but makes 4, so total gain of 2 ATP per glucose broken
Makes 2 pyruvate from 1 glucose
Preparatory Reaction
Occurs in matrix of mitochondria
Each pyruvate is broken into CO2 and C2 acetyl group, which binds to coenzyme A to produce acetyl CoA
NADH is produced
Citric Acid Cycle
Occurs in matrix of mitochondria
Acetyl CoA is oxidized to CO2
NADH and FADH2 are produced
ATP is produced
Electron transport chainOccurs in cristae of mitochondria
Series of carriers that pass electrons from one to the next
NADH and FADH2 are the sources of the electrons, but the chain does not accept the H+, only the e-
Final acceptor for electrons is the O2 that we breathe in!
Electron transport chain
Energy released as electrons move down the chain is used to make ATPs
NAD and FAD are recycled to be used again
Electron transport chainWhat about the H+?
The energy released by the ETC is used to pump H+ into the inter-membrane space, between inner and outer membranes of mitochondria
This creates a gradient- more H+ in inter-membrane space than in matrix
Electron transport chainLike in photosynthesis, this gradient results in potential energy that can be used
ATP synthase exists in cristae
H+ flows back into matrix through synthase, which makes ATP from the energy
Electron transport chain
Produces 34 ATP from each glucose that originally entered the cycle
ETC ATP plus ATP made earlier= 38 ATP per glucose
This is about 40% of energy in glucose, the rest is lost as heat
FermentationCellular respiration requires O2 as the final acceptor in the electron transport chain, but what if no O2 is available?
Pyruvate is reduced to make lactate, H+ comes from NADH
Only makes 2 ATP- what is the point?
Fermentation
Regeneration of NAD keeps glycolysis going, instead of stalling (=death)
Can create short bursts of energy
Why you are sore after strenuous work
Yeasts use fermentation and generate ethyl alcohol instead of lactate