1. Chapter 9 Chemical Pathways
Cellular Respiration
Honors Biology
Chapter 9
Chemical Pathways

2. Basic Need for Energy
Energy in Food: What is the difference between a: calorie(lower case c) and Calorie (upper case C)?
A calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree C.
A Calorie is a kilocalorie, or 1000 calories
For example, 1 gram of glucose releases 3811 calories, on a food label 3.8 Calories

3. Basic Need for Energy
Energy in Food:
The reason we eat is to get energy
We get carbohydrates from our food which are broken into Glucose
Organisms cannot use glucose directly, it must be broken down into smaller units…… ATP

4. Overview of Cellular Respiration
The process that releases energy by breaking down glucose and other food molecules in the presence of O2
The equation for cellular respiration is exactly the opposite of photosynthesis.
6 O2 + C6H12O6  6 CO2 + 6 H2O and energy

6. Breaking Down Energy Slowly:
Glucose needs to be broken down in small steps so that energy is not wasted.

7. First Step: Glycolysis
Definition: The process of breaking the glucose in half to form 2 molecules of pyruvate, a 3 carbon chain.
First step of cellular respiration
Uses 2 ATP to start reaction
Produces 4 ATP and 2 NADH
Occurs in the Cytosol (not mitochondria)

8. Glycolysis

9. Why use ATP in Glycolysis if you want ATP?
You have to use a little energy to make even more energy.
Like a bank, you put money in to earn interest.
Net ATP gained per glucose molecule=2
Animation

10. Glycolysis
NAD+ and NADH can be compared to NADP+ and NADPH in photosynthesis.
Useful because they hold electrons

11. Glycolysis Benefits: No Oxygen needed
Very Fast – thousands of ATP produced in milliseconds

12. Glycolysis Stops when it runs out of NAD+ (electron carrier)
Disadvantages:
Stops when it runs out of NAD+ (electron carrier)
If oxygen is available: Cellular respiration tarts
If oxygen is NOT available, to make more NAD+, your body goes through fermentation.
This way ATP can be made even without Oxygen.

13. Alcoholic Fermentation Lactic Acid Fermentation
Fermentation is releasing energy in the absence of oxygen. It is an ANAEROBIC (no oxygen) process.
Ultimately it allows NADH to be converted to NAD+, allowing glycolysis to continue.
There are two main types of fermentation
Alcoholic Fermentation
Lactic Acid Fermentation

14. Alcohlic fermentAtion

15. Alcoholic Fermentation
Alcoholic fermentation is found in Yeast, and a few other microorganisms when no Oxygen is available
The equation is:
Pyruvic acid + NADH  alcohol + CO2 + NAD+
Note: Carbon Dioxide is also produced, so when yeast conducts fermentation, there is the release of carbon dioxide as well as alcohol.

16. Alcoholic Fermentation
Alcoholic fermentation diagram

17. Alcohlic fermentAtion

18. Lactic Acid Fermentation

19. Lactic Acid Fermentation
Pyruvic acid from glycolysis can be converted to lactic acid.
This conversion regenerates NAD+ for glycolysis to continue
Pyruvic acid + NADH  lactic acid + NAD+
Lactic acid fermentation is used by muscles when they run out of oxygen, ultimately causing soreness.
Lactic acid is also created by unicellular organisms in the production of cheese, pickles, kimchi and other foods.

20. Lactic Acid Fermentation
Lactic Acid fermentation diagram

21. Pyruvate

23. Glycolysis
Alcoholic Fermentation
Lactic Acid Fermentation
Does is need Oxygen? NO
Reactant?
Glucose
Pyruvic acid (Pyruvate)
Is ATP made?
(How Many?) 2
Is NAD+ made?
NO- used 2
Yes-2
Product (s)
2 Pyruvic Acid (Pyruvate)
2 ATP, 2 NADH
CO2, Alcohol, NAD+
Lactic Acid, NAD+

24. Krebs Cycle and Electron Transport
After glycolysis, 90% of chemical energy originally in glucose still remains locked in pyruvic acid
O2 is one of the most powerful electron acceptors and will help release the rest of the 90%
If O2 is available to the cell, pyruvic acid heads to Krebs Cycle after glycolysis
Krebs Cycle breaks pyruvic acid into CO2

26. Krebs Cycle Where does it occur: Mitochondria
It requires oxygen – it is AEROBIC
It is also known as the Citric Acid Cycle

27. Pyruvic acid enters mitochondria and 1 carbon becomes part of CO2
Krebs Cycle
Pyruvic acid enters mitochondria and 1 carbon becomes part of CO2
Electrons and H+ join NAD+ becoming NADH
The 2 remaining carbons join coenzyme A to form acetyl-CoA
Acetyl-CoA adds to a 4-carbon molecule producing citric acid
Animation

28. The citric acid is broken down to a 5- then 4- carbon molecule
Krebs Cycle
The citric acid is broken down to a 5- then 4- carbon molecule
Electrons and H+ join NAD+ and FAD to become NADH and FADH2
2 CO2 molecules are released and 1 ATP made
So far, from 1 glucose
Glycolysis produced: 2 NADH and 2 ATP
Krebs Cycle produced: 8 NADH and 2 FADH2 and 2 ATP
Animation

29. Krebs Cycle (AKA Citric Acid Cycle)
Totals
Glycolysis:
2 ATPs
2 NADH
Kreb :
8 NADH
2 FADH2

31. What happens to the Krebs cycle products?
Carbon Dioxide is released to the atmosphere
ATP is used for cellular activities
NADH and FADH2 are used in the electron transport chain (next step) to produce large amounts of ATP

32. Electron Transport Chain
Uses the high energy electrons from the Krebs cycle to convert ADP into ATP

33. Electron Transport Chain
Where does it occur: Inner membrane of the Mitochondria
It requires oxygen – it is AEROBIC

34. Electron transport chain

36. Electron Transport Chain
NADH and FADH transfer electrons to carrier proteins
Electrons move down the chain, allowing H+ to move across through protein channels
At the end of the chain, O2 accepts electrons and left over H+, creating water, H2O
Animation

37. Electron Transport Chain
The H+ builds on the outside of the membrane
The H+ moves through ATP synthase, spinning the protein
Each rotation charges an ADP, attaches a phosphate, and creates ATP
Animation

38. Cellular Respiration totals
So far, from 1 glucose
Glycolysis: 2 ATP
Krebs Cycle: 2 ATP
Electron Transport: 32 ATP
Totals: 36 ATP from 1 glucose molecule
This is 38% efficienct
The rest of the energy is released as heat: reason why you feel warmer after exercise

39. Cells contains small amounts of ready ATP
Energy use by humans
Cells contains small amounts of ready ATP
About 5 seconds worth (first 50-meters of sprint)
After that, your body uses lactic acid formation
This lasts for about 90 seconds
Maybe make meters
Only way to get rid of lactic acid is a chemical pathway that requires Oxygen (heavy breathing)

40. Energy use by humans
For exercise longer than 90 seconds, cellular respiration is used
This is a slow method to generate ATP
Glycogen (a form of carbohydrate stored in muscles) is broken down and used for the first minutes of cellular respiration
After that other molecules, such as fats, are broken down