1. INTRODUCTION TO CELLULAR RESPIRATION
SBI 4U: Metablic Processes
INTRODUCTION TO CELLULAR RESPIRATION
The majority of organisms on earth use glucose as their main energy source. Through a series of redox reactions glucose is broken down and free energy is released
Aerobic Cellular Respiration is the most often used method of converting glucose to free energy.
Aerobic means that oxygen is used in the process. Respiration does not refer to the act of breathing or gas exchange in the lungs, but the 20 or so reactions that take place to free up the energy in glucose.
Section 1.3

2. SBI 4U: Metablic Processes
OXIDATION OF GLUCOSE
Oxygen oxidizes the C-H in glucose (and fatty acids) in two ways:
If you look at the 12 H in glucose they are broken away to form water. The electrons in a C-H bond are equally shared, in water the electrons are drawn closer to oxygen, therefore H is oxidized (LEO). The electrons move from a less electronegative atom (H) to a more electronegative one (O).
The same thing happens to the 6C glucose who are drawn into 6CO2.
Overall the oxidation of glucose moves electrons from a higher free energy state to a lower free energy state, thereby decreasing potential energy.
Section 1.3

3. Oxidation of glucose produces 2870 kJ/mol of 25 degrees Celsius and kPa (Lab conditions; 3012 kJ/mol in a real cell).
About 34% of this energy is trapped by the cell and used to fuel endergonic processes. The rest dissipates as heat or light.
Figure 2 on page 92.
Oxygen and glucose are stable molecules. They do not readily react with one another. Lots of activation energy is needed (flame in lab conditions).
Enzymes catalyze each reaction step thereby reducing the activation energy and making it easier for the cell to undergo aerobic cellular respiration.

4. SBI 4U: Metablic Processes
AEROBES AND ANAEROBES
Oxygen is not the only primary electron acceptor at the end of the respiration process, other molecules such as NO2, SO4, CO2, and Fe3+ are used in some forms of bacteria to help undergo respiration (obligate anaerobes)
Animals are obligate aerobes since they use oxygen as their final electron acceptor.
Organisms that can tolerate the presence and absence of oxygen are called facultative aerobes (mostly bacteria).
Section 1.3

5. SBI 4U: Metablic Processes
AEROBIC RESPIRATION
In aerobic respiration there are three main goals:
break the bonds of glucose freeing the carbon to make CO2
break the bonds of glucose freeing H to form water
to trap as much free energy as possible in the form of ATP
The entire process occurs in 4 main stages: Glycolysis, Pyruvate Oxidation, Krebs Cycle and the Electron Transport Chain (Figure 1 on page 94) and involves 2 types of phosphorylation: substrate-level phosphorylation and oxidative phosphorylation.
Section 1.3

6. Two Types of Phosphorylation
Substrate-Level Phosphorylation is the formation of ATP directly in an enzyme-catalyzed reaction. A phosphate containing compound transfers its phosphate group to ADP (forming ATP) directly on an enzyme.
4 molecules of ATP are formed this way in glycolysis and 2 in the Krebs cycle for every one glucose.
Oxidative Phosphorylation is the indirect formation of ATP. It involves a series of redox reactions in which oxygen is the final electron acceptor. It is more complex than Substrate-Level Phosphorylation and therefore creates more ATP.
The reduction of the electron carrying molecules NAD+ and FAD to NADH and FADH2 are energy harvesting reactions that will transfer the majority of their free energy to the creation of ATP.

7. GLYCOLYSIS Name means sugar-splitting
First 10 reactions of cellular respiration
It occurs in the cytoplasm and is anaerobic.
Each reaction is catalyzed by a specific enzyme.
(The reactions are shown in figure 11 on page 98, as well as your handouts).
Glycolysis produces 2.1% of the entire free energy of glucose in aerobic cellular respiration.
Glycolysis is thought to have been the earliest form of energy metabolism.

8. Steps in Glycolysis
Steps 1-5: Two ATP are used (step 1 and step 3). This primes glucose for cleavage in steps 4 and 5. (6 carbons)
Step 4/5: Fructose 1, 6-biphosphate is split into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P) and immediately the enzyme isomerase changes DHAP into G3P. (3 carbons)
Steps 6 through 10 happen twice (one for each molecule of G3P).
In step 6, NAD+ is reduced to NADH + H+
Step 7: Two ATP molecules are produced by substrate level phosphorylation. One for each 1,3-bisphophoglycerate (BPG) processed.
Step 10: Phosphoenolpyruvate (PEP) is converted into pyruvate; this produces ATP by substrate-level phosphorlyation. (3 carbon)
Net-reaction: glucose + 2ADP + 2P + 2NAD --> 2 pyruvate + 2ATP + 2NADH + 2H+