1. 9.2 The Process of Cellular Respiration
Lesson Overview
9.2 The Process of Cellular Respiration

2. Cellular respiration
Breaking down sugar in the presence of oxygen (aerobic) to produce ATP.

3. Glycolysis Summary What happens during the process of glycolysis?
During glycolysis, 1 molecule of glucose, a 6-carbon compound, is transformed into 2 molecules of pyruvic acid, a 3-carbon compound.

4. Glycolysis
Cellular respiration begins with glycolysis 1. Glycolysis occurs in the cytoplasm 2. Reactants = glucose, 2 NAD+, 2 ATP, 3. Products = 2 pyruvates, 2 NADH, 4 ATP (Net 2 ATP), NAD+ = nicotinamide adenine dinucleotide – a co-enzyme necessary for the reaction to go forward, H+ donator in the electron transport chain During glycolysis NAD+ is reduced to NADH.

5. Glycolysis Glycolysis is the first stage of cellular respiration.
Glycolysis means “sugar-breaking”
During glycolysis, glucose (a 6-carbon sugar) is broken down into 2 molecules of the 3-carbon molecule pyruvic acid.
Pyruvic acid is a reactant in the Krebs cycle.
ATP and NADH are produced as part of the process.

6. The Advantages of Glycolysis
Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase.
Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.

7. The Krebs Cycle What happens during the Krebs cycle?
During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.

8. The Krebs Cycle
During the Krebs cycle, the second stage of cellular respiration, pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions.
The Krebs cycle is also known as the citric acid cycle because citric acid is the first compound formed in this series of reactions.

9. Krebs Cycle Occurs in the matrix of the mitochondria
Reactants = 2 acetyl CoA, 2 ADP, 6 NAD+, 2 FAD
Products = 2 ATP, 6 NADH, 2 FADH2, 4 CO2
For every glucose molecule that starts cell respiration, 2 pyruvates are formed, forming 2 acetyl CoAs
FAD – flavin adenine dinucleotide – co-enzyme necessary for the reaction as well as an electron donor in the electron transport chain
During Krebs cycle both NAD+ & FAD are reduced to NADH & FADH2 respectively

10. Electron Transport and ATP Synthesis
How does the electron transport chain use high-energy electrons from glycolysis and the Krebs cycle?
The electron transport chain uses the high-energy electrons from glycolysis and the Krebs cycle to convert ADP into ATP.

11. Electron transport System
Occurs in within the inner membrane of the mitochondria
Reactants = 6 NADH, 2 FADH2, 6 O2, ADP
Products = approximately 36 – 38 ATPs, 4 H2O

12. The Totals How much energy does cellular respiration generate?
Together, glycolysis, the Krebs cycle, and the electron transport chain release about 36 molecules of ATP per molecule of glucose.

13. Energy yield from glucose metabolism
Glycolysis – 2 ATP Krebs Cycle – 2 ATP 2 NADH from glycolysis – 4 ATP 2 NADH from transition step – 6 ATP 6 NADH from Krebs Cycle – 18 ATP 2 FADH2 from Krebs Cycle – 4 ATP
TOTAL 36 ATP

14. 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.

15. Energy Totals
The cell can generate ATP from just about any source, even though we’ve modeled it using only glucose. Complex carbohydrates are broken down into simple sugars like glucose. Lipids and proteins can be broken down into molecules that enter the Krebs cycle or glycolysis at one of several places.