1. Chapter 9 Cellular Respiration and Fermentation

2. Chemical Energy and Food
Where do organisms get energy?
Organisms get the energy they need from food.
A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius.

3. Cellular Respiration
Cellular Respiration is the process that releases energy from food in the presence of oxygen.
In symbols:
6 O2 + C6H12O6  6 CO2 + 6 H2O + Energy
In words:
Oxygen + Glucose  Carbon dioxide + Water + Energy
The cell has to release the chemical energy in food molecules (like glucose) gradually, otherwise most of the energy would be lost in the form of heat and light.

4. Comparing Photosynthesis and Cellular Respiration
Photosynthesis removes carbon dioxide from the atmosphere, and cellular respiration puts it back.
Photosynthesis releases oxygen into the atmosphere, and cellular respiration uses that oxygen to release energy from food.

5. Stages of Cellular Respiration
The three main stages of cellular respiration are:
glycolysis,
the Krebs cycle, and
the electron transport chain.

6. 9.2 The Process of Cellular Respiration

7. Glycolysis Word literally means “sugar-breaking.”
During glycolysis, 1 molecule of glucose (a 6-carbon compound) is transformed into 2 molecules of pyruvic acid (a 3-carbon compound).
ATP Production
At the pathway’s beginning – 2 ATP molecules are used up
The 2 ATP molecules are like an investment that pays back interest. In order to earn interest from a bank, first you have to put money into an account.
Although the cell put 2 ATP molecules into its “account” to get glycolysis going, glycolysis produces 4 ATP molecules.
This is a net gain of 2 ATP molecules

8. Glycolysis NADH Production
One of the reactions during glycolysis removes 4 electrons, now in a high energy state, and passes them to an electron carrier called NAD+, or nicotinamide adenine dinucleotide.
Similar to NADP+ in photosynthesis, each NAD+ accepts a pair of high- energy electrons.
Now NADH, holds electrons until transferred to other molecules.
In the presence of oxygen, these high-energy electrons can be used to produces even more ATP molecules.

9. Glycolysis The Advantage of Glycolysis
In process, 4 ATP molecules are made from 4 ADP molecules
2 ATP molecules needed to begin reaction gives a net gain of 2 ATP molecules.
Produces only a small amount of energy, but happens so fast that cells can produce thousands of ATP molecules in a few milliseconds.
Speed a big advantage when energy demands of the cell increase
Another advantage – does not require oxygen
Glycolysis can quickly supply chemical energy when oxygen is not available
When oxygen is available – pyruvic acid and NADH “outputs” generated during glycolysis become the “inputs” for other processes of cellular respiration

11. The Krebs Cycle
Names after Hans Krebs, the British biochemist who demonstrated its existence in 1937.
During the Krebs Cycle, pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions.
Also known as the Citric Acid Cycle
Citric Acid Production
Pyruvic acid produced by glycolysis passes through the two membranes of the mitochondria and into the matrix
Matrix – the innermost compartment of the mitochondrion and the site of the Krebs cycle reactions.
1 carbon atom from pyruvic acid becomes part of CO2
The other 2 carbon atoms from pyruvic acid form acetic acid, which is joined to a compound called coenzyme A. This makes acetyl-CoA.
As the Krebs Cycle begins, acetyl CoA combines with a 4-carbon compound in the Krebs Cycle to produce citric acid (6 carbons)

12. The Krebs Cycle Energy Extraction
Through a series of reactions citric acid is broken down –
Into a 5-carbon compound – CO2 released
Into a 4-carbon compound – CO2 released
4-carbon compound can then start the cycle over again by combining with acetyl-CoA
Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2
What happens to each of these Krebs Cycle products?
CO2 not useful to the cell and is expelled every time you exhale
ATP – very useful – power other cellular activities
NADH – in the presence of oxygen, the electrons they hold are used to generate huge amounts of ATP.

14. Electron Transport and ATP Synthesis
Uses electrons from NADH (from glycolysis) and NADH and FADH2 (from the Krebs Cycle) to power it.
The electron transport chain uses high-energy electrons from glycolysis and the Krebs Cycle to convert ADP into ATP.
Electron Transport
High energy electrons from NADH and FADH2 are passed from carrier to carrier, down the ETC.
Water is formed when oxygen accepts electrons and hydrogen ions.
Energy generated by the electron transport chain is used to move H+ ions across the inner mitochondrial membrane and into the inter- membrane space.
H+ ions build up in the inter-membrane space, making in positively charged.
The matrix side of the membrane, from which the H+ ions have been taken, is now negatively charged.

15. Electron Transport and ATP Synthesis
ATP Production
The cell uses these charge differences to produce ATP.
JUST LIKE PHOTOSYNTHESIS, the inner mitochondrial membrane contains enzymes known as ATP Synthases.
The charge difference forces H+ ions through ATP Synthase, causing it to spin.
With each spin, ATP Synthase grabs an ADP molecule and attached a phosphate group, producing ATP!!!!!!!
Every time a pair of high energy electrons move down the ETC, the energy is used to move H+ ions across the membrane. These ions rush back across with enough force to spin ATP Synthase and generate enormous amounts of ATP!!!
On average, each pair of high-energy electrons produces enough energy to produce 3 molecules of ATP.

19. Energy Totals
In the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules.
This represents about 36 percent of the total energy of glucose. The remaining 64 percent is released as heat.
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20. Fermentation
Fermentation is a process by which energy can be released from food molecules in the absence of oxygen.
Fermentation occurs in the cytoplasm of cells.

21. Alcoholic Fermentation
Yeast and a few other microorganisms use alcoholic fermentation that produces ethyl alcohol and carbon dioxide.
This process is used to produce alcoholic beverages and causes bread dough to rise.

22. Lactic Acid Fermentation
Most organisms, including humans, carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid.
Used during periods without oxygen
Lactic acid – used to produce pickles and sauerkraut – contributes the familiar sour taste.

23. Energy and Exercise
How does the body produce ATP during different stages of exercise?
For short, quick bursts of energy, the body uses ATP already in muscles as well as ATP made by lactic acid fermentation.
For exercise longer than about 90 seconds, cellular respiration is the only way to continue generating a supply of ATP.

24. Quick Energy
Lactic acid fermentation can supply enough ATP to last about 90 seconds. However, extra oxygen is required to get rid of the lactic acid produced.
Following intense exercise, a person will huff and puff for several minutes in order to pay back the built-up “oxygen debt” and clear the lactic acid from the body.

26. Long-Term Energy
For intense exercise lasting longer than 90 seconds, cellular respiration is required to continue production of ATP.
Cellular respiration releases energy more slowly than fermentation does.
The body stores energy in the form of the carbohydrate glycogen. These glycogen stores are enough to last for 15 to 20 minutes of activity. After that, the body begins to break down other stored molecules, including fats, for energy.
Hibernating animals like this brown bear rely on stored fat for energy when they sleep through the winter.