1. Cellular Respiration
Releasing Chemical Energy
Chapter 6

2. BIOCHEMICAL REACTIONS
• All living organisms require a constant supply of
energy to sustain life.
• Cellular respiration - the chemical energy stored in
glucose is converted into a more usable form – ATP
– Requires the presence of oxygen and the correct enzymes
– Carbon dioxide, water and heat are also released as by-products
of this reaction.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)
glucose + oxygen → carbon + water + energy
dioxide

3. Why Cell “Respiration”?
2. This process requires oxygen,
which is supplied by breathing
3. The mechanical movement of air
or water through the lungs/gills is
often referred to as ventilation
to distinguish it from respiration.
4. What about plants?

5. • Cellular respiration
– slow, controlled
release of energy
(max. harvest of
energy from food)

6. Review of ATP

7. Review of ATP
• ATP is the “energy currency/rechargeable
batteries” of cells
• When energy is harvested from a chemical
reaction or sunlight, it is stored when a
phosphate group is attached to an ADP to form
ATP.
– Called phosphorylation

8. • When the ATP is broken back down to ADP, stored
chemical energy is released to do work in a cell
– Called dephosphorylation
– Some energy is lost as heat

10. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)
glucose + oxygen → carbon + water + energy
dioxide

11. OXIDATION REACTIONS
• Oxidation begins in the cytoplasm and is
completed in the mitochondria
• 3 parts to cellular respiration (each an
enzyme-controlled pathway)
– Glycolysis
– Krebs cycle
– Electron transport
system

12. Overview

13. • Animation:
http://www.qcc.cuny.edu/BiologicalScienc
es/Faculty/DMeyer/respiration.html

14. 1. Glycolysis - a 6C glucose molecule is broken
into 2 3C molecules of pyruvate (pyruvic acid)
a. Occurs in the cytoplasm of the cell – near the mitochondria
b. Yields: + 2 ATP (4 ATP – 2ATP - used to phosphorylate
glucose when it enters cell)
+ 2 NADH (NAD+ is reduced to NADH)
c. This process is anaerobic (without oxygen)…can happen even
if there is an insufficient O2 level to carry out the rest of cellular
respiration

15. If there is O2
present, respiration continues. Each
3C pyruvate will…
2. Lose atoms of carbon and oxygen – CO2
released
(…it is now called an acetyl group)
4. Join to a molecule of coenzyme A (which is a
B vitamin) – Acetyl CoA
- CoA acts as a shuttle, carrying acetyl groups
3. NAD+ (coenzyme that shuttles around
hydrogen and electrons) is reduced to NADH.
4. These reactions are often called the
‘Intermediate Reactions’

17. 2. Kreb’s Cycle (Citric Acid Cycle)
a. Acetyl CoA enters the mitochondrion and 2C
acetyl group bonds to a 4C compound
(oxaloacetate) to form a 6C compound
called Citric Acid (citrate)

18. b. The 6C compound is broken down to a 5C
compound
1 CO2 is produced
1 NAD+ is reduced to NADH

19. c. 5C compound is broken down into a 4C compound
1 CO2 is produced
1 NAD+ is reduced to NADH
d. Oxaloacetate is regenerated (4C  4C)
This yields:
1 ATP (ADP  ATP)
1 FADH2 (FAD  FADH2)
1 NADH (NAD+  NADH)

20. e. So, the total yield of just the Kreb’s cycle is:
2 ATP
6 NADH
2 FADH2 per glucose

22. 3. Electron transport
system (ETS) makes
ATP
a. Electrons from
reduced coenzymes
NADH and FADH2
are transferred
through a series of
redox reactions until
the electrons are
accepted by oxygen to
make water.

23. b. Mitochondrial
structure
1) Double membrane-
bound organelle
2) Inner membrane
folded into christae
a) Increase surface
area for reactions
b) ETS located here
• Intermembrane
space
• Matrix - Kreb’s cycle

24. c. ATP synthesis
1. H atoms from coenzymes
dropped off at ETS (inner
membrane)
2. H atoms split into a proton
(H+) and an electron (e-)
- Electrons go through ETS
- Energy from electrons is
used to pump the H+ out
into the intermembrane
space
3. H+ concentration in this
space increases
4. The H+ RUSH back into
the matrix (because of
concentration gradient)
through an H+ channel
(ATP synthetase
complex) making ATP
5. Called chemiosmosis

27. • Animation:
http://vcell.ndsu.nodak.edu/animations/atpgr
adient/movie.htm

28. d. Happy endings…
1. H+ and e- (now low energy) are rejoined
2. H atoms bond to available oxygen atoms and form water:
H+ + e - + O2  H2O
This is why you breathe!! The O2 is merely a hydrogen dump!
O2 allows the continual movement of H+ through the ATP
synthetase
No O2, no rushing H+ movement, no ATP, no life!

29. e. ETS produces: (per glucose)
2 NADH (from glycolysis)
2 NADH (from intermediate reactions) +
6 NADH (Krebs cycle)______________
10 NADH x 3 ATP/NADH = 30 ATP
2 FADH2 x 2 ATP/ FADH2 = 4 ATP____
for a total 34 ATP/glucose from ETS

30. Cellular Respiration Energy
Summary
34 ATP/glucose from ETS +
2 ATP (glycolysis) +
2 ATP (Krebs cycle)_______________
38 ATP per glucose!!!

32. • Prisoners’ explanation

33. • Current applications

34. • Other nutrients can
be used for energy
– Lipids fatty acids,
enter Krebs Cycle
– Proteins amino
acids
• NH3 removed urea
• Carbon portions enter
Krebs Cycle as
oxaloacetate
– Carbon skeletons can
be used for
biosynthesis of amino
acids, nucleic acids
and fatty acids

35. Alternatives to Aerobic Respiration
What if there’s not enough oxygen?

36. Glycolysis still happens (since it’s
anaerobic anyway…).
- Yield is 2 ATP + 2 NADH + 2 pyruvic
acid (3 C molecule).
- Fate of the pyruvic acid depends on what
type of organism you are…

37. If you are a plant or yeast cell…
Pyruvic acid will become ETHANOL in a process
called alcoholic fermentation.

39. If you are a bacterial cell…
Your pyruvic acid can be fermented to
vinegar or to start the process of
cheesemaking.

40. If you are an animal cell…
Your pyruvic acid becomes LACTIC ACID in
a process called lactic acid
fermentation.

42. Photosynthesis and Cellular
Respiration
• Cellular respiration and photosynthesis
share several features:
– They are enzyme-controlled biochemical
pathways.
– They make use of ATP for energy transfer
– They use an Electron Transport System to
help make ATP.

43. Photosynthesis and Cellular
Respiration

44. Photosynthesis and Cellular
Respiration
Light + 6 CO2 + 6 H2O → C6H12O6 + 6 O2
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy
(ATP + heat)

45. • End of cellular respiration!

46. Acetyl CoA
NADH
FADH
NADPH

47. CELLULAR RESPIRATION
• Breakdown of glucose molecules in the presence of
oxygen.
• The oxidation of glucose (by many enzymes)
results in carbon dioxide and water.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)
glucose + oxygen → carbon + water + energy
dioxide

48. A Definition of Cellular Respiration
The energy stored in glucose (with the
presence of oxygen and the correct
enzymes) is converted into a more usable
form – ATP. Carbon dioxide and water
are also released as by-products of this
reaction.
C6H12O6 + 6 O2  6 CO2 + 6 H2O + ATP
[Read the last paragraph on page 131]

49. GLYCOLYSIS
• Glucose (6 carbons) is broken into two
3 carbon molecules called pyruvate
(pyruvic acid).
• This makes enough energy to make 2
ATP molecules.
• In addition, an NADH molecule is also
made and transferred to the electron
transport chain.

52. 3. Electron transport system
(ETS), located in the
membranes of
mitochondria (and
chloroplasts) makes ATP.
– High-energy electrons are
passed stepwise through a
series of oxidation-
reduction reactions from
one carrier molecule to
another.
• Every time the electron is
passed, some of its energy is
released and can be used to
make ATP
• The rest of the energy is
released as heat

53. How much energy do you get from
1 molecule of glucose?
Glycolysis – 2ATP and 2 NADH (each x3)
Intermediate – 2 NADH (each x3)
Kreb’s Cycle – 2 ATP, 6 NADH (each x3),
and 2 FADH2 (each x2)
The ETS yields 8 ATP from glycolysis, 6
ATP from the Intermediate Reactions, 24
ATP from the Kreb’s Cycle
For a total of…
38 ATP per initial molecule of glucose

54. Throughout the process, coenzymes
are being reduced so, in the end, they
can all be oxidized (so ATP can be
generated!) – sort of like POKER!

56. CELLULAR RESPIRATION
SUMMARY
• Glucose is broken
down to carbon
dioxide and water,
making 4 ATPs
directly and another
32 ATP via the
electron transport
system.