1. Chemical Pathways
Chapter 9 Section 1

2. Chemical Energy and Food
How much energy is really in food?
One gram of sugar glucose releases 3811 calories of heat energy
Calorie: Amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius
Calorie on the food labels is a kilocalorie, or 1000 calories

3. Chemical Energy and Food
Cells don’t burn glucose……Then why is it so important????
Process begins with a pathway called Glycolysis
Glycolysis releases only a small amount of energy
If oxygen is present, it prepares the glucose molecule

4. Overview of Cellular Respiration
Cellular Respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen
Processes of Cellular Respiration:
Glycolysis
Kreb’s Cycle
Electron Transport Chain

5. Overview of Cellular Respiration

6. Glycolysis 1st stage of Cellular Respiration Occurs in the cytoplasm
Glycolysis is the process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid
At the beginning of glycolysis, 2 ATP molecules are put in to get the process started
When glycolysis is finished, 4 ATP molecules are gained
Net ATP: 4 (created) – 2 (invested)=2 ATP

7. Glycolysis
One of the reactions that makes ATP also makes another high energy molecule, NADH
An electron carrier, NAD+, accepts a pair of high-energy electrons to form NADH
2 Pyruvic acid will then go onto either the Kreb’s cycle (if oxygen is present) or fermentation (if oxygen is not present)

8. Glycolysis Advantage: Disadvantage: Speed
Does not require oxygen (produces thousands of ATP in milliseconds
Disadvantage:
Will run out of NAD+

9. Overview of Glycolysis
Reactants:
Glucose
2 ATP
4 ADP
2 NAD+
Products:
2 Pyruvic Acid
4 ATP
2 ADP
2 NADH
H2O

11. Fermentation
When oxygen is not present, pyruvic acid moves to fermentation
Since fermentation does not require oxygen, it is said to be anaerobic
Fermentation recycles NADH back to NAD+ for glycolysis
Two main types of fermentation:
Alcoholic Fermentation
Lactic Acid Fermentation

12. Alcoholic Fermentation
Yeast and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide
Used by bakers to cause bread to rise or brewers to make beer
Pyruvic Acid +NADH→Alcohol +CO2+NAD+

13. Lactic Acid Fermentation
In many cells, the pyruvic acid accumulated can be converted into lactic acid
Lactic acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissues
Buildup of lactic acid is the burning, painful sensation in your muscles
Some prokaryotes produce lactic acid to produce: cheese, yogurt, buttermilk, sour cream, pickles, and sauerkraut
Pyruvic Acid +NADH→Lactic Acid +NAD+