Cellular Respiration
Harvesting Chemical Energy
Harvesting stored energy
•	Glucose is the model
•	catabolism of glucose to produce ATP
How do we move electrons in biology?
•	Moving electrons in living systems
•	electrons cannot move alone in cells
•	electrons move as part of H atom
•	move H = move electrons
“OIL RIG”
•	Oxidation Is Lost.
•	Reduction Is Gained 
•	(when you gain negative electrons, you reduce the charge on the atom)
Moving electrons in respiration
•	Electron carriers move electrons by 
shuttling H atoms around “SHUTTLES”
•	NAD^+ → NADH (reduced)
•	FAD^+2 → FADH_2 (reduced)

Glycolysis 
•	Breaking down glucose 
•	“glyco – lysis” (splitting sugar)

									
•	ancient pathway which harvests energy
•	where energy transfer first evolved
•	transfer energy from organic molecules to ATP
•	still is starting point for all cellular respiration
•	but it’s inefficient 
•	generate only 2 ATP for every 1 glucose
•	occurs in cytosol
Evolutionary perspective
•	Prokaryotes
•	first cells had no organelles
•	Anaerobic atmosphere
•	life on Earth first evolved without free oxygen (O_2) in atmosphere
•	energy had to be captured from organic molecules in absence of O_2
•	Prokaryotes that evolved glycolysis are ancestors of all modern life
•	ALL cells still utilize glycolysis
Overview
10 reactions
•	convert 
glucose (6C) to 
2 pyruvate (3C) 
•	produces: 
4 ATP & 2 NADH
•	consumes:
2 ATP
•	net: 
2 ATP & 2 NADH
Substrate-level Phosphorylation
•	In the last steps of glycolysis, where did the P come from to make ATP?
•	the sugar substrate (PEP)
Is that all there is?
•	Not a lot of energy… Only 2 ATP!
•	for over a 1 billon years^+ this is how life on Earth survived!!
•	no O_2=  slow growth, slow reproduction
•	only harvest 3.5% of energy stored in glucose
•	more carbons to strip off = more energy to harvest
We can’t stop there!
•	Going to run out of NAD^+
•	without regenerating NAD+, 
energy production would stop!
•	another molecule must accept 
H from NADH
How is NADH recycled to NAD^+?
Another molecule must accept H from NADH
Pyruvate is a branching point
Pyruvate
Cellular Respiration
	Stage 2 & 3:
		Oxidation of Pyruvate
		Krebs Cycle
Mitochondria — Structure
•	Double membrane energy harvesting organelle
•	smooth outer membrane
•	highly folded inner membrane
•	cristae
•	intermembrane space
•	fluid-filled space between membranes
•	matrix
•	inner fluid-filled space
•	DNA, ribosomes
•	enzymes
Mitochondria – Function
Pyruvate oxidized to Acetyl CoA 

Energy accounting of Krebs cycle 
Net gain	=	2 ATP
 		=	8 NADH + 2 FADH_2
Cellular Respiration
	Stage 4: 
		Electron Transport Chain
There is a better way!
•	Electron Transport Chain 
•	series of molecules built into inner mitochondrial membrane
•	along cristae
•	transport proteins & enzymes 
•	transport of electrons down ETC linked to pumping of H^+ to create H^+ gradient
•	yields ~34 ATP from 1 glucose!
•	only in presence of O_2 (aerobic respiration)
Electron Transport Chain
Stripping H from Electron Carriers
•	NADH passes electrons to ETC
•	H cleaved off NADH & FADH_2
•	electrons stripped from H atoms → H^+ (protons)
•	electrons passed from one electron carrier to next in mitochondrial membrane (ETC)
•	transport proteins in membrane pump H^+ (protons) across inner membrane to intermembrane space
We did it!
•	Set up a H^+ gradient
•	Allow the protons 
to flow through ATP synthase
•	Synthesizes ATP

ADP + P_i → ATP
Chemiosmosis
•	The diffusion of ions across a membrane
•	build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP
Cellular respiration