1. Making energy!
ATP
The Point is to Make ATP!

2. Chapter 9 Warm-Up Define:
Glycolysis
Respiration
Chemiosmosis
Phosphorylation
Fermentation
Electrochemical gradient
FAD  FADH2
NAD+ NADH
Explain “glycolysis”. Where does it occur? How does it “work”?

3. Chapter 9 Warm-up
What is the chemical equation for cellular respiration?
Remember OILRIG
In the conversion of glucose and oxygen to CO2 and H2O, which molecule is reduced?
Which is oxidized?
What happens to the energy that is released in this redox reaction?
NAD+ is called a(n) ________________.
Its reduced form is _________.

4. Chapter 9 Warm-Up
Why is glycolysis considered an ancient metabolic process?
Where in the cell does glycolysis occur?
What are the reactants and products of glycolysis?
Which has more energy available:
ADP or ATP?
NAD+ or NADH?
FAD+ or FADH2?

5. Chapter 9 Warm-Up Where does the Citric Acid Cycle occur in the cell?
What are the main products of the CAC?
How is the proton gradient generated?
What is the purpose?
Describe how ATP synthase works.
In cellular respiration, how many ATP are generated through
Substrate-level phosphorylation?
Oxidative phosphorylation?

6. Chapter 9 Warm-Up
In fermentation, how is NAD+ recycled?

7. What you need to know: The summary equation of cellular respiration.
The difference between fermentation and cellular respiration.
The role of glycolysis in oxidizing glucose to two molecules of pyruvate.
The process that brings pyruvate from the cytosol into the mitochondria and introduces it into the citric acid cycle.
How the process of chemiosmosis utilizes the electrons from NADH and FADH2 to produce ATP.

8. Chapter 9. Cellular Respiration and Fermentation

9. What’s the point?
ATP
The Point is to Make ATP!

10. Harvesting stored energy
Energy is stored in organic molecules
heterotrophs eat food (organic molecules)
digest organic molecules
serve as raw materials for building & fuels for energy
controlled release of energy
series of step-by-step enzyme-controlled reactions
“burning” fuels
carbohydrates, lipids, proteins, nucleic acids
We eat to take in the fuels to make ATP which will then be used to help us build biomolecules and grow and move and… live!
heterotrophs = “fed by others”
vs.
autotrophs = “self-feeders”

11. Harvesting energy stored in glucose
Glucose is the model
catabolism of glucose to produce ATP
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6
6O2
6CO2
6H2O
ATP  +
+ heat
respiration
Movement of hydrogen atoms from glucose to water
combustion = making heat energy by burning fuels in one step
respiration = making ATP (& less heat) by burning fuels in many small steps
ATP
fuel (carbohydrates)
CO2 + H2O + heat
CO2 + H2O + ATP (+ heat)

12. How do we harvest energy from fuels?
Digest large molecules into smaller ones
break bonds & move electrons from one molecule to another
as electrons move they carry energy with them
that energy is stored in another bond, released as heat, or harvested to make ATP
They are called oxidation reactions because it reflects the fact that in biological systems oxygen, which attracts electrons strongly, is the most common electron acceptor.
Oxidation & reduction reactions always occur together therefore they are referred to as “redox reactions”.
As electrons move from one atom to another they move farther away from the nucleus of the atom and therefore are at a higher potential energy state.
The reduced form of a molecule has a higher level of energy than the oxidized form of a molecule. The ability to store energy in molecules by transferring electrons to them is called reducing power, and is a basic property of living systems.
loses e-
gains e-
oxidized
reduced + – + + e-
oxidation
reduction e-

13. How do we move electrons in biology?
Moving electrons
in living systems, electrons do not move alone
electrons move as part of H atom
loses e-
gains e-
oxidized
reduced + – + + H
Energy is transferred from one molecule to another via redox reactions.
C6H12O6 has been oxidized fully == each of the carbons (C) has been cleaved off and all of the hyrogens (H) have been stripped off & transferred to oxygen (O) — the most electronegative atom in livng systems. This converts O2 into H2O as it is reduced.
The reduced form of a molecule has a higher energy state than the oxidized form. The ability of organisms to store energy in molecules by transferring electrons to them is referred to as reducing power. The reduced form of a molecule in a biological system is the molecule which has gained a H atom, hence NAD+  NADH once reduced.
soon we will meet the electron carriers NAD & FADH = when they are reduced they now have energy stored in them that can be used to do work.
oxidation
reduction H
C6H12O6
6O2
6CO2
6H2O
ATP  +
oxidation
reduction H

14. Coupling oxidation & reduction
Redox reactions in respiration
release energy as breakdown molecules
break C-C bonds
strip off electrons from C-H bonds by removing H atoms
C6H12O6  CO2 = fuel has been oxidized
electrons attracted to more electronegative atoms
in biology, the most electronegative atom?
O2  H2O = oxygen has been reduced
release energy to synthesize ATP
 O2
O2 is 2 oxygen atoms both looking for electrons
LIGHT FIRE ==> oxidation
RELEASING ENERGY
But too fast for a biological system
C6H12O6
6O2
6CO2
6H2O
ATP  +
oxidation
reduction

15. Oxidation & reduction Oxidation Reduction  removing H
loss of electrons
releases energy
exergonic
Reduction
adding H
gain of electrons
stores energy
endergonic
C6H12O6
6O2
6CO2
6H2O
ATP  +
oxidation
reduction

16. Overview of cellular respiration
4 metabolic stages
Anaerobic respiration
1. Glycolysis
respiration without O2
in cytosol
Aerobic respiration
respiration using O2
in mitochondria
2. Pyruvate oxidation
3. Kreb’s cycle
4. Electron transport chain
C6H12O6
6O2
6CO2
6H2O
ATP  +
(+ heat)

17. What’s the point?
ATP
The Point is to Make ATP!

18. Glycolysis “sugar splitting”
Believed to be ancient (early prokaryotes- no O2 available)
Occurs in cytosol
Partially oxidizes glucose (6C) to 2 pyruvates (3C)
Net gain: 2 ATP and 2 NADH
Also makes 2H2O
No O2 required

19. glucose      pyruvate
Glycolysis
Breaking down glucose
“glyco – lysis” (splitting sugar)
most ancient form of energy capture
starting point for all cellular respiration
inefficient
generate only 2 ATP for every 1 glucose
in cytosol
why does that make evolutionary sense?
glucose      pyruvate 6C 2x 3C
Why does it make sense that this happens in the cytosol?
Who evolved first?

20. Evolutionary perspective
Life on Earth first evolved without free oxygen (O2) in atmosphere
energy had to be captured from organic molecules in absence of O2
Organisms that evolved glycolysis are ancestors of all modern life
all organisms still utilize glycolysis
You mean, I’m related to them?!
The enzymes of glycolysis are very similar among all organisms. The genes that code for them are highly conserved.
They are a good measure for evolutionary studies. Compare eukaryotes, bacteria & archaea using glycolysis enzymes.
Bacteria = 3.5 billion years ago
glycolysis in cytosol = doesn’t require a membrane-bound organelle
O2 = 2.7 billion years ago
photosynthetic bacteria / proto-blue-green algae
Eukaryotes = 1.5 billion years ago
membrane-bound organelles!
Processes that all life/organisms share:
Protein synthesis
Glycolysis
DNA replication

21. Glycolysis Stage 1: Energy Investment Stage
Cell uses ATP to phosphorylate compounds of glucose
Stage 2: Energy Payoff Stage
Two 3-C compounds oxidized
For each glucose molecule:
2 Net ATP produced by substrate-level phosphorylation
2 molecules of NAD+  NADH

22. Overview glucose C-C-C-C-C-C fructose-6P P-C-C-C-C-C-C-P DHAP P-C-C-C
activation energy
10 reactions
convert 6C glucose to two 3C pyruvate
produce 2 ATP & 2 NADH
2 ATP
2 ADP
fructose-6P
P-C-C-C-C-C-C-P
DHAP
P-C-C-C
PGAL
C-C-C-P
1st ATP used is like a match to light a fire…
initiation energy / activation energy.
Destabilizes glucose enough to split it in two
2 NAD+
2 NADH
4 ADP
4 ATP
Substrate level
phosphorylation
pyruvate
C-C-C

23. Glycolysis summary endergonic invest some ATP exergonic
harvest a little more ATP
& a little NADH
Glucose is a stable molecule it needs an activation energy to break it apart.
phosphorylate it = Pi comes from ATP.
make NADH & put it in the bank for later.

24. Substrate-level Phosphorylation
In the last step of glycolysis, where did the P come from to make ATP?
P is transferred from PEP to ADP
kinase enzyme
ADP  ATP
I get it!
The P came directly from the substrate!

25. Energy accounting of glycolysis
2 ATP
2 ADP
glucose      pyruvate 6C 2x 3C
4 ADP
4 ATP
All that work! And that’s all I get?
And that’s how life subsisted for a billion years.
Until a certain bacteria ”learned” how to metabolize O2; which was previously a poison.
But now pyruvate is not the end of the process
Pyruvate still has a lot of energy in it that has not been captured.
It still has 3 carbons bonded together! There is still energy stored in those bonds. It can still be oxidized further.
Net gain = 2 ATP
some energy investment (2 ATP)
small energy return (4 ATP)
1 6C sugar  2 3C sugars

26. Heck of a way to make a living!
Is that all there is?
Not a lot of energy…
for 1 billon years+ this is how life on Earth survived
only harvest 3.5% of energy stored in glucose
slow growth, slow reproduction
Heck of a way to make a living!
So why does glycolysis still take place?

27. We can’t stop there…. Glycolysis NADH glucose + 2ADP + 2Pi + 2 NAD+ 
2 pyruvate + 2ATP + 2NADH
Going to run out of NAD+
How is NADH recycled to NAD+?
without regenerating NAD+, energy production would stop
another molecule must accept H from NADH
NADH

28. How is NADH recycled to NAD+?
Another molecule must accept H from NADH
anaerobic respiration
ethanol fermentation
lactic acid fermentation
aerobic respiration
NADH

29. Anaerobic ethanol fermentation
Bacteria, yeast 1C 3C 2C
pyruvate  ethanol + CO2
NADH
NAD+
beer, wine, bread
at ~12% ethanol, kills yeast
Animals, some fungi
Count the carbons!!
Lactic acid is not a dead end like ethanol. Once you have O2 again, lactate is converted back to pyruvate by the liver and fed to the Kreb’s cycle.
pyruvate  lactic acid 3C
NADH
NAD+
cheese, yogurt, anaerobic exercise (no O2)

30. Pyruvate is a branching point
fermentation
Kreb’s cycle
mitochondria

31. Glycolysis (summary)

32. What’s the point?
ATP
The Point is to Make ATP!

33. Mitochondrion Structure

34. Cellular Respiration

35. Glycolysis is only the start

36. pyruvate    acetyl CoA + CO2
Oxidation of pyruvate
Pyruvate enters mitochondria
3 step oxidation process
releases 1 CO2 (count the carbons!)
reduces NAD  NADH (stores energy)
produces acetyl CoA
Acetyl CoA enters Krebs cycle
where does CO2 go?
NAD
NADH 3C 2C 1C
pyruvate    acetyl CoA + CO2 [ 2x ]
Waiting to exhale?

37. Pyruvate oxidized to Acetyl CoA
reduction
oxidation
Yield = 2C sugar + CO2 + NADH

38. Krebs cycle

39. reduction of electron carriers and
Count the carbons and electron carriers!
pyruvate 3C 2C
acetyl CoA
citrate 4C 6C
NADH x2 4C 6C
This happens twice for each glucose molecule
CO2
reduction of electron carriers and
oxidation of sugars
NADH 5C 4C
CO2
FADH2 4C 4C
NADH
ATP

40. Whassup? So we fully oxidized glucose C6H12O6  CO2
& ended up with 4 ATP!
What’s the Point?

41. What’s so important about NADH?
NADH & FADH2
Krebs cycle produces large quantities of electron carriers
NADH
FADH2
stored energy!
go to ETC
What’s so important about NADH?

42. Citric Acid Cycle (Krebs)
Occurs in mitochondrial matrix
Acetyl CoA→ Citrate→
Net gain: 2 ATP, 6 NADH, 2 FADH2 (electron carrier)
ATP produced by substrate-level phosphorylation
CO2

43. So why the Krebs cycle? If the yield is only 2 ATP, then why?
value of NADH & FADH2
electron carriers
reduced molecules store energy!
to be used in the Electron Transport Chain

44. What’s the point?
ATP
The Point is to Make ATP!

45. Cellular respiration

46. There’s got to be a better way!
ATP accounting so far…
Glycolysis  2 ATP
Kreb’s cycle  2 ATP
Life takes a lot of energy to run, need to extract more energy than 4 ATP!
There’s got to be a better way!
What’s the Point?

47. That sounds more like it!
There is a better way!
Electron Transport Chain
series of molecules built into inner mitochondrial membrane
mostly transport proteins
transport of electrons down ETC linked to ATP synthesis
yields ~34 ATP from 1 glucose!
only in presence of O2 (aerobic)
That sounds more like it!

48. Mitochondria Double membrane * form fits function! outer membrane
inner membrane
highly folded cristae*
fluid-filled space between membranes = intermembrane space
matrix
central fluid-filled space
* form fits function!

49. Electron Transport Chain

50. Remember the NADH? Kreb’s cycle Glycolysis 8 NADH 2 FADH2 2 NADH PGAL

51. Electron Transport Chain
NADH passes electrons to ETC
H cleaved off NADH & FADH2
electrons stripped from H atoms  H+ (H ions)
electrons passed from one electron carrier to next in mitochondrial membrane (ETC)
transport proteins in membrane pump H+ across inner membrane to intermembrane space
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.

52. electrons flow downhill to O2
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
electrons flow downhill to O2

53. Electrons flow downhill
Electrons move in steps 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

54. Why the build up H+? ATP synthase ADP + Pi  ATP
enzyme in inner membrane of mitochondria
ADP + Pi  ATP
only channel permeable to H+
H+ flow down concentration gradient = provides energy for ATP synthesis
molecular power generator!
flow like water over water wheel
flowing H+ cause change in shape of ATP synthase enzyme
powers bonding of Pi to ADP
“proton-motive” force

55. ATP synthesis Oxidative phosphorylation
Chemiosmosis couples ETC to ATP synthesis
build up of H+ gradient just so H+ could flow through ATP synthase enzyme to build ATP
Oxidative
phosphorylation
So that’s the point!

56. Summary of cellular respiration
C6H12O6
6O2
6CO2
6H2O
~36 ATP  +
Where did the glucose come from?
Where did the O2 come from?
Where did the CO2 come from?
Where did the H2O come from?
Where did the ATP come from?
What else is produced that is not listed in this equation?
Why do we breathe?
Where did the glucose come from?
from food eaten
Where did the O2 come from?
breathed in
Where did the CO2 come from?
oxidized carbons cleaved off of the sugars
Where did the H2O come from?
from O2 after it accepts electrons in ETC
Where did the ATP come from?
mostly from ETC
What else is produced that is not listed in this equation?
NAD, FAD, heat!

57. Taking it beyond…
What is the final electron acceptor in electron transport chain? O2
So what happens if O2 unavailable?
ETC backs up
ATP production ceases
cells run out of energy
and you die!
What if you have a chemical that punches holes in the inner mitochondrial membrane?

58. What’s the point?
ATP
The Point is to Make ATP!

59. Any Questions??

60. Glycolysis Fermentation Respiration
O2 present
Without O2
Without O2
Fermentation
Respiration
Keep glycolysis going by regenerating NAD+
Occurs in cytosol
No oxygen needed
Creates ethanol [+ CO2] or lactate
2 ATP (from glycolysis)
Release E from breakdown of food with O2
Occurs in mitochondria
O2 required (final electron acceptor)
Produces CO2, H2O and up to 32 ATP

61. Various sources of fuel
Carbohydrates, fats and proteins can ALL be used as fuel for cellular respiration
Monomers enter glycolysis or citric acid cycle at different points

62. aerobic cellular respiration
ENERGY
aerobic cellular respiration
(with O2)
anaerobic (without O2)
glycolysis
(cytosol)
mitochondria
Fermentation
(cytosol)
pyruvate oxidation
ethanol + CO2
(yeast, some bacteria)
citric acid cycle
substrate-level phosphorylation
lactic acid
(animals)
ETC
oxidative phosphorylation
chemiosmosis