1. Section 9.3 Getting Energy to make ATP

2. Overview:

3. *Remember, humans do not have chlorophyll in their skin, therefore they cannot use light energy to make ATP like a plant does. Instead, we have mitochondria in our cells that can convert carbohydrates, like those made by plants, into ATP.
Cellular Respiration
1. Definition - cellular respiration is the process by which mitochondria break down food molecules to produce ATP.
2. 3 stages of cellular respiration:
a) glycolysis
b) citric acid cycle (Krebs Cycle)
c) electron transport chain

4. 3 Parts of Cellular Respiration:

5. *Glycolysis is anaerobic and thus does not require oxygen; the citric acid cycle and ETC are aerobic therefore oxygen is needed for them to occur.
A. Glycolysis
1. Definition - glycolysis is a series of reactions in
the cytoplasm of a cell in which glucose (a 6
carbon molecule) is broken down into two
molecules of pyruvic acid (3 carbon molecules).
2. ATP - it takes 2 molecules of ATP to start the
process of glycolysis, and only 4 ATPs are made,
therefore this process is not very energy efficient.

6. *only 2 molecules of ATP are produced from the breakdown of one glucose molecule.
3. NAD+ (nicotinamide dinucleotide) - just as
photosynthesis has the energy carrier NADP+;
glycolysis has an energy carrier called NAD+.
*NAD+ forms NADH when carrying an electron.
4. At the end of glycolysis the pyruvic acid
molecules produced move to the mitochondria,
the powerhouses or ATP producers of the cell.

7. Glycolysis

8. Molecular details of glycolysis

9. 5. Post-glycolysis reactions - before the pyruvic acid molecules can enter the citric acid cycle (the next stage of cellular respiration) some modifications need to be done.
a) pyruvic acid loses a molecule of CO2 and
combines with Coenzyme A to form a molecule
of Acetyl-CoA.
b) the rxn w/ Coenzyme A makes a molecule of
NADH + H+

10. Post-glycolysis Reactions: Formation of Acetyl-CoA

11. B. The Citric Acid Cycle: “The breakdown of Glucose”
1. Definition - the citric acid cycle is a series of chemical reactions similar to the Calvin Cycle, but opposite in purpose.
Calvin Cycle - forms glucose in photosynthesis
Citric Acid Cycle - breaks down glucose in
cellular respiration
2. Materials needed :
to break down glucose, two electron carriers are
needed:
a) NAD+
b) FAD (flavin adenine dinucleotide)

12. 3. What’s formed:
The Citric Acid Cycle (CAC) produces a number
of molecules:
a) 1 ATP is produced
b) 3 NADH + H+ are produced
c) 1 FADH2 molecule is produced

13. 4. Steps of the Citric Acid Cycle (CAC):
a) formation of citric acid - a 2 carbon acetyl CoA
combines w / 4 carbon compound called
oxaloacetic acid, forming a 6 carbon molecule
called citric acid.
b) formation of CO2 - one molecule of CO2 is
formed from the citric acid cycle which reduces
the citric acid molecule to a 5 carbon molecule
called ketoglutaric acid.
*from this rxn, one molecule of NADH +
H+ is made from one NAD+

14. c) formation of second CO2 - another molecule of CO2 is formed and released from the ketoglutaric acid; this results in a 4 carbon compound called succinic acid.
*from this rxn, one molecule of ATP and one
molecule of NADH + H+ are formed.
d) recycling of oxaloacetic acid - succinic acid undergoes a series of rxns which form FADH and NADH + H+ and oxaloacetic acid; this is then available for the next cycle to occur.
Succinic -> fumaric -> malic -> oxaloacetic

15. The Citric Acid Cycle (CAC):

17. Hans Krebs

18. C. The Electron Transport Chain:
1. Function - move energized molecules; NADH & FADH2 pass energized molecules from protein to protein releasing small amounts of energy with each pass.
2. Location - the inner membrane of the mitochondria

19. The Mitochondria:

20. a) NADH & FADH2 pass energized molecules
ETC:
3. The Process:
a) NADH & FADH2 pass energized molecules
from protein to protein; small amounts of
energy are released with each pass.
b) some energy is used to form ATP, while some
is used to pump H+ ions into the center of the
mitochondria.
c) as H+ ions are pumped into the center of the
mitochondria, the center becomes more (+),
while the outside becomes more (-). Since
the outside is more (-) it will attract more (+)’s
or more H+ ions,creating an electrochemical
gradient.

21. d) The electrochemical gradient drives the inner membrane of the mitochondria to form ATP.
e) The final electron acceptor in the ETC is Oxygen. The oxygen reacts with H+ ions to form water molecules.
* this is why our bodies need Oxygen

22. The Electron Transport Chain in the Mitochondria

23. Another view of the ETC

24. 4. The importance of Oxygen (O2)
If oxygen is not available for the ETC, then the chain cannot pass along energized electrons; if electrons cannot be passed, then there is no room to accept more electrons and a blockage results. Therefore, cellular respiration cannot occur.
5. Overall production
The ETC results in the production of 32 ATP molecules
This is the most efficient means for production of ATP
Think: Aerobic (jogging) vs, Anaerobic (sprinting) - which can be done longer?

25. II. Fermentation
*sometimes your cells may be deprived of oxygen for a short time
*fermentation can occur during extremely strenuous activities
1. Fermentation - anaerobic process that occurs when your cells are w/o O2 for a short time. It occurs after glycolysis and provides a way to continue producing ATP until oxygen is available again.
2. 2 main types of fermentation:
a) lactic acid fermentation
b) alcoholic fermentation

26. Lactic Acid Fermentation
*occurs during anaerobic conditions when oxygen is not available as the final electron acceptor in the ETC, therefore a “back-up” occurs.
1. What happens:
a) as NADH and FADH2 try to pass their
energized electrons onto the next protein in the
ETC, they are rejected.
b) if NADH and FADH2 cannot pass on their
energized electrons, then NADH and FADH2
cannot be converted back to NAD+ & FAD, which
are needed to keep the CAC and glycolysis
going.

27. c) the cell has no way of replacing FAD during anaerobic conditions, but NAD+ can be replaced via Lactic acid fermentation.
d) in lactic acid fermentation, 2 molecules of pyruvic acid (from glycolysis) use NADH to form 2 molecules of lactic acid.
e) when the NADH is used to make lactic acid, which is becomes stored in the muscles, NAD+ is released and can be reused in glycolysis to make 2 more ATP molecules.
f) the lactic acid is then transferred from the muscle cells to the liver where it is changed back into pyruvic acid.

28. Lactic Acid Fermentation:
*when lactic acid builds up in muscle cells it causes fatigue; you feel as though you “hit a wall” or have “jello legs”

29. B. Alcoholic Fermentation
*often used by yeast cells to produce CO2 and ethyl alcohol.
*anaerobic process - used to make bread dough “rise” and brew alcohols.

30. III. Comparing Photosynthesis and Cellular Respiration
*both use an ETC to form ATP
*do opposite jobs:
photosynthesis - produces high energy
carbohydrates and O2 from the
sun’s energy
cellular respiration - uses O2 to break down
carbohydrates with much lower
energy level

31. Photosynthesis Cellular Respiration Comparisons:
Food is made or accumulated
Food is Broken down
Energy from sun is stored as glucose
Energy from glucose is released to be used by body
Carbon dioxide (CO2) is taken in
CO2 is given off as a waste product
Oxygen (O2) is given off as waste
Oxygen is needed and is taken in
Produces glucose from PGAL
Produces CO2 and H2O as waste
Can happen only when some light is available
Can occur all day and all night
Requires Chlorophyll, can only happen in plants
Occurs in all living cells - plants and animals