1. Chapter 9: Cellular Respiration

2. Chemical Energy and Food
Food = chemical building blocks living things need to grow and reproduce
Broken down gradually
Capture little bits of energy at key steps
Use energy stored in chemical bonds of foods to produce ATP which powers the activities of the cell

3. Overview of Cellular Respiration:
It is the process that releases energy by breaking down food molecules in the presence of oxygen
6O2 + C6H12O6  6CO2 + 6H2O + energy (ATP)
oxygen + glucose  carbon dioxide + water + energy (ATP)
A cell needs to trap those little pieces of energy to make ATP
Takes 3 main steps
Glycolysis
Krebs Cycle (Citric Acid Cycle)
Electron Transport System

4. Step 1: Glycolysis = “sugar breaking” Glucose  Pyruvate (pyruvic acid)
The beginning of the energy pathway in respiration
Takes place in the CYTOPLASM
One molecule of glucose is broken in half, producing 2 molecules of pyruvic acid (a 3-carbon compound)
Uses 2 ATP molecules to get the process started
In the end 4 molecules will have been produced
Net gain = 2 molecules of ATP (a relatively small amount)

5. Step 1: Glycolysis Glucose  Pyruvate
Produces
2 molecules of pyruvate
2 molecules of ATP
Advantages
Happens quickly – can produce 1000s of ATPs in a few milliseconds
Does not require oxygen
If oxygen is present leads to 2 other pathways that release lots of energy = aerobic respiration
If no oxygen, a different pathway is followed = anaerobic respiration

6. Aerobic Respiration (oxygen present)

7. Step 2: Krebs Cycle (Citric Acid Cycle)
Occurs in the mitochondria
Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions
1st step – citric acid production
Pyruvic acid passes through the mitochondrial membrane into the matrix
Pyruvic acid – CO2 = Acetyl CoA
Acetyl CoA + 4-C compound = Citric Acid

8. Step 2: Krebs Cycle (Citric Acid Cycle)
Cha-Ching –O- Meter
ATP
NADH
FADH2
2nd step – stepwise energy extraction, release of CO2 at each step
4-C molecule replenished at end, cycle can continue

9. Step 3: Electron Transport Chain
Cha-Ching –O- Meter
ATP
NADH
FADH2
Occurs in the MITCHONDRIAL MEMBRANE
High energy electrons arrive in NADH and FADH2 from Krebs and Gylcolysis
Movement of electrons down the ETC moves H into the mitochondrial membrane, establishes a concentration gradient
Hydrogen moves back out through ATP synthase, spinning
the turbine and
creating ATP (massive
amounts of ATP!!!)
Requires O2; oxygen is
the final electron
acceptor at the end
of the ETC
Approximately ATPs are generated for every glucose

10. Overview of Cellular Respiration
It is the process that releases energy by breaking down food molecules in the presence of oxygen
6O2 + C6H12O6 6CO2 + 6H2O + Energy
oxygen + glucose carbon dioxide + water + energy
A cell needs to trap those little pieces of energy to make ATP
Takes 3 main steps – glycolysis, krebs cycle, electron transport system

11. The beginning of the energy pathway in respiration
Step 1: Glycolysis
The beginning of the energy pathway in respiration
The process in which one molecule of glucose is broken in half, producing 2 molecules of pyruvic acid (a 3-carbon compound)
Uses 2 ATP molecules to get the process started
In the end 4 molecules will have been produced
Net gain = 2 molecules of ATP (a relatively small amount)
If oxygen is present leads to 2 other pathways that release lots of energy = aerobic respiration
If no oxygen, a different pathway is followed = anaerobic respiration

12. Aerobic Respiration – oxygen present

13. Step 2: Krebs Cycle/Citric Acid Cycle
90% of the chemical energy available in glucose is still unused at the end of glycolysis
It is locked in the pyruvic acid
Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions
1st step – citric acid production
2nd step – energy extraction

14. Step 3: Electron Transport Chain
Uses the high energy electrons from the Krebs cycle to convert ADP into ATP
Don’t worry about all the steps
Produces 34 more ATP molecules per glucose

16. Summary of ATP totals

17. Why do we need all this ATP?
Cells need energy to work
Primary fuel is ATP (adenosine triphosphate)
ATP = nitrogen containing compound (adenine), 5-carbon sugar (ribose), and 3 phosphate groups
ADP = same as ATP but with 2 phosphate groups
The 3rd phosphate is the key to how cells store energy – when the cell has extra energy available it adds a phosphate to make 3 and when it needs energy it can take a phosphate away
Releasing Energy from ATP
Energy is released from ATP when ATP is changed into ADP + phosphate
ATP = compressed spring (unstable)
ADP = relaxed spring (stable)
Using Biochemical Energy
Active transport
Powers movement of organelles within the cell
ATP and Glucose
Cells only contain a small store of ATP because it is not efficient
Sugar can store up to 90 times the energy than ATP
Cells use the energy in carbohydrates to generate ATP form ADP as needed

18. Anaerobic Respiration – no oxygen present
Alcoholic Fermentation
Used by yeasts and a few other microorganisms
Pyruvic acid + NADH alcohol + CO2 + NAD+
Cause bread dough to rise
When the yeast runs out of oxygen , it begins to ferment, giving off carbon dioxide
Makes the bread rise by forming small air pockets in the bread
Alcohol evaporates when the bread is baked
Lactic Acid Fermentation
If pyruvic acid accumulates it can be converted to lactic acid
Pyruvic acid + NADH lactic acid + NAD+
Lactic acid is produced in your muscles when you exercise when the body can’t supply enough oxygen to the tissues
Your muscles start to produce ATP by lactic acid fermentation and lactic acid builds up in your muscles causing a painful burn

19. Photosynthesis vs. Respiration
Almost opposite reactions
Photosynthesis deposits energy
Respiration withdraws energy
The products of photosynthesis are the reactants for respiration
Respiration takes place in all eukaryotes and some prokaryotes
Photosynthesis takes place in plants, algae, and some bacteria