1. Cellular Respiration Stage 2:Oxidation of Pyruvate Stage 3: Krebs Cycle Stage 4: ETC

2. Cellular respiration

3. Mitochondria Structure
Double membrane
highly folded inner membrane called cristae
Importance: increases surface area
Fluid filled interior called “matrix”
DNA, ribosomes, enzymes
Site of the Krebs Cycle
intermembrane
space
inner
membrane
outer
matrix
cristae
mitochondrial DNA

4. Mitochondria – Form fits Function
Divide like bacteria
Supports endosymbiosis
Membrane-bound proteins
passive & active transport
Almost all eukaryotic cells have mitochondria
there may be 1 very large mitochondrion or 100s to 1000s of individual mitochondria
number of mitochondria is correlated with aerobic metabolic activity
more activity = more energy needed = more mitochondria
What cells would have a lot of mitochondria?
Active cells:
• muscle cells
• nerve cells
Internal folds
Advantage = more surface area

5. Stage 2: Oxidation of pyruvate
Pyruvate enters mitochondria
Pyruvate OXIDIZED and forms acetyl CoA
releases 1 CO2
reduces 2 NAD+  2 NADH [ 2x ]
pyruvate    acetyl CoA + CO2 3C
NAD 2C 1C
CO2 is fully oxidized carbon == can’t get any more energy out it
CH4 is a fully reduced carbon == good fuel!!!

6. Stage 3: Krebs Cycle Aka citric acid cycle
What? oxidation/reduction process that forms CO2 and H2O [wastes]
Where? Matrix of mitochondria
Significance  evolved later than glycolysis, but fundamental to aerobic respiration

7. OXIDATION – in the presence of O2 - aerobic
Produces:
CO2 and H2O
energy carriers [8 NADH and 2 FADH2]
2 net ATP

8. Electron Carriers = Hydrogen Carriers
NADH
FADH2
go to Electron Transport Chain
ADP + Pi
ATP

9. Energy accounting of Krebs cycle2x
4 NAD + 1 FAD
4 NADH + 1 FADH2
pyruvate          CO2
1 ADP
1 ATP 3C 3x 1C
ATP
Net gain = 2 ATP
= 8 NADH + 2 FADH2

10. Electron carriers are important because they …
Set up a H+ gradient
allow H+ to flow through ATP synthase
ADP + Pi  ATP
ADP P +
ATP

11. Stage 4: Electron Transport Chain

12. ETC
transport proteins and enzymes are built into inner mitochondrial membrane [cristae]
transport electrons down ETC using protons donated by energy carriers (NADH, FADH)
yields ~34 ATP from 1 glucose
only in presence of O2 (aerobic respiration) O2

13. Time to break open the bank!
glucose
Krebs cycle
Glycolysis
PGAL
8 NADH
2 FADH2
Time to break open the bank!

14. Electron Transport Chain
Building proton gradient!
NADH  NAD+ + H p e
intermembrane space H+ H+ H+
inner mitochondrial membrane
H  e- + H+ C Q e– e– e– H
FADH2
FAD H 1 2
NADH
2H+ + O2
H2O
NAD+
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
mitochondrial matrix

15. Stripping H from Electron Carriers
NADH and FADH pass electrons to ETC
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
NAD+ Q C
NADH
H2O H+ e–
2H+ + O2
FADH2 1 2
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
FAD H+
Oxidation refers to the loss of electrons to any electron acceptor, not just to oxygen.
Uses exergonic flow of electrons through ETC to pump H+ across membrane.
ADP + Pi
ATP

16. O2 is 2 oxygen atoms both looking for electrons
But what “pulls” the electrons down the ETC?
Pumping H+ across membrane … what is energy to fuel that?
Can’t be ATP! that would cost you what you want to make!
Its like cutting off your leg to buy a new pair of shoes. :-(
Flow of electrons powers pumping of H+
O2 is 2 oxygen atoms both looking for electrons O2
oxidative phosphorylation

17. Electrons flow downhill
Electrons move from carrier to carrier downhill to O2
each carrier more electronegative
controlled oxidation
controlled release of energy
Electrons move from molecule to molecule until they combine with O & H ions to form H2O
It’s like pumping water behind a dam -- if released, it can do work

18. H+ gradient Allows protons to flow through ATP synthase
ADP + Pi
Allows protons to flow through ATP synthase
Synthesizes ATP
ADP + Pi  ATP
ATP

19. Chemiosmosis links the Electron Transport Chain to ATP synthesis
The diffusion of ions across a membrane
build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP
Chemiosmosis links the Electron Transport Chain to ATP synthesis
Chemiosmosis is the diffusion of ions across a membrane. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane.
Hydrogen ions (protons) will diffuse from an area of high proton concentration to an area of lower proton concentration. Peter Mitchell proposed that an electrochemical concentration gradient of protons across a membrane could be harnessed to make ATP. He likened this process to osmosis, the diffusion of water across a membrane, which is why it is called chemiosmosis.

20. Pyruvate from cytoplasm synthase Krebs cycle Mitochondrial matrix+ Q C 32
ATP 2
Pyruvate from
cytoplasm
Electron
transport
system
synthase
H2O
CO2
Krebs
cycle
Intermembrane
space
Inner
mitochondrial
membrane
1. Electrons are harvested and carried to the transport system.
2. Electrons provide energy to pump protons across the membrane.
3. Oxygen joins with protons to form water.
2H+
NADH
Acetyl-CoA
FADH2
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
Mitochondrial
matrix 1 e-

21. Cellular respiration + +
2 ATP
2 ATP
~34 ATP