1. Cellular Respiration

2. Lesson Objectives Summarize the stages of cellular respiration
Identify the role of electron carriers in each stage of cellular respiration
Compare alcoholic fermentation and lactic acid fermentation

3. Main Idea
Living organisms obtain energy by breaking down organic molecules during cellular respiration.
Cellular respiration occurs in the mitochondria!

4. Overview Organisms obtain energy through cellular respiration.
The function of cellular respiration is to harvest electrons from carbon compounds, like glucose, and use that energy to make ATP.
Equation:
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
(opposite of photosynthesis)

5. Overview Cellular respiration occurs in two main parts:
Glycolysis
Aerobic respiration
Anaerobic respiration and processes do not require oxygen.
Aerobic respiration includes the Krebs cycle and electron transport and is an aerobic process.
Aerobic processes require oxygen.

6. Aerobic Respiration Must have oxygen to occur
Takes place in the mitochondria
Produces a net of 36 ATP molecules from one glucose molecule

7. Glycolysis
Series of reactions in the cytoplasm that breaks down glucose to pyruvic acid
Two molecules of ATP and two molecules of NADH are formed for each molecule of glucose.
Not very efficient
Anaerobic respiration
Uses NAD+ as its electron carrier
At end, pyruvate moves into the mitochondria

8. Glycolysis
Two phosphate groups (derived from two ATP) are joined to glucose. Energy is needed to start, hence the ATP!
The 6-carbon molecule is broken down into two 3-carbon molecules.
Two phosphates are added and electrons and hydrogen ions (H+) combine with two NAD+ molecules to form NADH (similar to the NADPH reaction).

9. Glycolysis
4. The two 3-carbon compounds are converted into two molecules of pyruvate.
4 ATP molecules are produced.
Only 2 ATP molecules are netted though
Why? 2 ATP molecules were used at the beginning so 4-2 = 2

11. The Citric Acid Cycle Aka the Krebs cycle
Most of the energy from the glucose is still contained in the pyruvate.
Series of reactions that occurs in the mitochondrial matrix that breaks down pyruvate into carbon dioxide.
One molecule of ATP is produced for every turn of the cycle
2 electron carriers used – NADH and FADH2
Passes electrons to the electron transport chain

12. The Citric Acid Cycle
Prior to the Krebs cycle, pyruvate first reacts with coenzyme A (CoA) to form a 2-carbon intermediate called acetyl CoA.
Carbon dioxide is released and NAD+ is converted to NADH.

13. The Citric Acid Cycle
The cycle begins with acetyl CoA combining with a 4-carbon compound to form a 6-carbon compound known as citric acid.
Citric acid is then broken down in the next series of steps, releasing two molecules of carbon dioxide and generating one ATP, three NADH, and one FADH2 (FAD is another electron carrier to NAD+ and NADP+).
Finally, acetyl CoA and citric acid are generated and the cycle continues.

14. The Citric Acid Cycle
Two pyruvate molecules are formed during glycolysis so there has to be two “turns” of the Krebs cycle.
Net yield:
6 carbon dioxide molecules
2 ATP
8 NADH
2 FADH2

16. Overview of ETC
1. Electrons are harvested and carried to the transport system.
2. Electrons provide energy to pump protons across the membrane.
3. Oxygen joins with protons to form water.
4. Protons diffuse back in, driving the synthesis of ATP.

17. Electron Transport Chain
Occurs in the inner membrane of the mitochondria
Produces the most ATP
NADH and FADH2 pass electrons from protein to protein, slowly releasing small amounts of energy by converting ADP into ATP.
As NADH and FADH2 release electrons, the energy carriers are converted to NAD+ and FAD, and H+ ions are dumped into the mitochondrial matrix.

18. Electron Transport Chain
The H+ ions are pumped into the mitochondrial matrix across the inner mitochondrial membrane.
H+ ions then diffuse down their concentration gradient back into the matrix through ATP synthase in chemiosmosis.
Oxygen is the final electron acceptor in the ETC in cellular respiration.

19. Electron Transport Chain
Protons and electrons are transferred to oxygen to form water.
Net yield from electron transport chain: 32 ATP
Net yield of aerobic respiration: 36 ATP

21. Anaerobic Respiration
No oxygen needed
Takes place in cytoplasm
Happens after glycolysis if all the NAD+ is used up and not replenished
Produces 2 ATP molecules from one glucose molecule

22. Fermentation Anaerobic process Occurs in the cytoplasm
Regenerates NAD+
2 main types:
Lactic acid
Alcoholic

23. Lactic Acid Fermentation
2 molecules of pyruvic acid use NADH to form two molecules of lactic acid
2 ATP molecules are formed for each glucose molecule
Transferred from muscle cells to the liver so that it can be converted back to pyruvic acid
Used to make cheese, yogurt, and sour cream

25. Alcoholic Fermentation
Used by yeast cells and some bacteria
Produces carbon dioxide and ethyl alcohol
Also gives off 2 ATP molecules
NADH donates electrons during this reaction and NAD+ is regenerated.

26. Photosynthesis vs. Cellular Respiration
Food accumulated
Energy from the sun is stored in glucose
Carbon dioxide taken in
Oxygen given off
Produces glucose from PGAL
Goes on only in light
Occurs in presence of chlorophyll
Cellular Respiration
Food broken down
Energy of glucose released
Carbon dioxide given off
Oxygen taken in
Produces carbon dioxide and water
Goes on day and night
Occurs in all living cells