1. INTRODUCTION
Cell respiration - means by which cells extract energy stored in food and transfer that energy to molecules of ATP.
Energy temporarily stored in ATP is instantly available for cellular activities:
electrical impulses
contracting a muscle
moving cilia
manufacturing a protein
The equation for the complete aerobic respiration of one molecule of glucose (seen below) is highly exergonic (releases energy).
C6H CO2 + 6H20 + energy

2. 2 types of cell respiration: anaerobic and aerobic
If oxygen is not present (anaerobic respiration), glycolysis is followed by either alcoholic fermentation or lactic acid fermentation.
If oxygen is present (aerobic respiration), glycolysis is only the first phase of aerobic respiration. It is followed by the Krebs cycle, the electron transport chain, and oxidative phosphorylation.

3. ATP-ADENOSINE TRIPHOSPHATE
ATP is unstable because the three phosphates in ATP are all negatively charged and repel one another.
When one phosphate group is removed by hydrolysis (the chemical breakdown of a compound due to reaction with water), a more stable molecule, ADP (adenosine diphosphate), results.
The change, from a less stable molecule to a more stable molecule, releases energy.

4. GLYCOLYSIS
Glycolysis literally means ‘glucose-splitting’ (glyco = glucose, lysis = splitting).
The first stage of aerobic respiration can occur with or without oxygen.
This step occurs in the cytoplasm of the cell.
10 step process that breaks down 1 molecule of glucose (a six-carbon molecule) into 2 three-carbon molecules of pyruvate or pyruvic acid and releases 4 molecules of ATP.
The energy activation for glycolysis is 2 ATP
After subtracting 2 ATPs from the 4 ATPs released from the reaction, the glycolysis of 1 molecule of glucose results in a net gain of 2 ATP.
2 ATP + 1 Glucose Pyruvate + 4 ATP

5. Glycolysis continued
The end product, pyruvate, is the raw material for the Krebs cycle, which is the next step in aerobic respiration.
During glycolysis, ATP is produced by substrate level phosphorylation—by direct enzymatic transfer of a phosphate to ADP. Only a small amount of ATP is produced this way.
The enzyme that catalyzes the third step, phosphofructokinase (PFK), is an allosteric enzyme. It inhibits glycolysis when the cell has enough ATP and does not need to produce any more.

6. ANAEROBIC RESPIRATION-FERMENTATION
Is an anaerobic, catabolic process that consists of glycolysis plus alcohol or lactic acid fermentation.
There are two types of anaerobes: facultative and obligate.
Facultative anaerobes can tolerate the presence of oxygen; they simply do not use it.
Obligate anaerobes cannot live in an environment containing oxygen.
• Yeast cells and some bacteria make ethanol and carbon dioxide.
• Other bacteria produce lactic acid/YOUR MUSCLE CELLS CAN FERMENT

7. Refresh Glycolysis A sequence of enzyme catalyzed reactions called :
YOU DO NOT NEED TO MEMORIZE THESE STEPS
Occurs in the cytoplasm
Net of 2 ATPs produced
2 Pyruvic acids formed
2NADH ( co enzyme)produced
Substrate Level Phosphorylation - the enzymatic transfer of a phosphate group from an organic molecule to adenosine diphosphate (ADP) to form adenosine triphosphate (ATP).

8. FORMATION OF ACETYL CO A
Before the Krebs Cycle begins
When oxygen is present, pyruvic acid is transported to the mitochondrion. Each pyruvic acid (a three-carbon molecule) is converted to acetyl coenzyme A (a two-carbon molecule) and CO2 is released:
2 Pyruvic acid + 2 Coenzyme A + 2 NAD+ --> 2 Acetyl CoA+ 2 CO2 + 2 NADH
-go from 2 three-carbon molecules to 2 two-carbon molecules. The extra carbons leave the cell in the form of CO2. Once again, two molecules of NADH are also produced.

9. The citric acid cycle -a cyclical series of enzyme-catalyzed reactions- AKA the Krebs cycle
1st step- acetyl co-A combines with oxaloacetic acid (OAA or oxaloacetate) to produce citric acid.
Remember each glucose is broken down to 2 pyruvates during glycolysis. Therefore, the respiration of each molecule of glucose causes the Krebs cycle to turn two times.
Pyruvate must first combine with coenzyme A (a vitamin) to form acetyl co-A, which does enter the Krebs cycle. The conversion of pyruvate to acetyl co-A produces 2 molecules of NADH, 1 NADH for each pyruvate.
Each turn of the Krebs cycle releases 3 NADH, 1 ATP, 1 FADH, and the waste product CO2, which is exhaled. (Remember, two turns of the Krebs cycle occur per glucose molecule.)
During the Krebs cycle, ATP is produced by substrate level phosphorylation—direct enzymatic transfer of a phosphate to ADP.

10. NAD AND FAD NAD and FAD are vitamin derivatives.
•NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinudeotide) are coenzymes that carry protons or electrons from glycolysis and the Krebs cycle to the electron transport chain.
•The enzyme NAD or FAD facilitates the transfer of hydrogen atoms from a substrate, such as glucose, to its coenzyme NAD+.
•Without NAD+ to accept protons and electrons from glycolysis and the Krebs cycle, both processes would cease and the cell would die.
•NAD+ is the oxidized form. NADH is the reduced form. -NADH carries 1 proton and 2 electrons.
•FAD is the oxidized form. FADH2 is the reduced form.

11. Electron Transport Chain- ETC
•The ETC is a collection of molecules embedded in the cristae membrane of the mitochondrion.
•There are thousands of copies of the ETC in every mitochondrion due to the extensive folding of cristae membrane.
The ETC carries electrons delivered by NAD and FAD from glycolysis and the Krebs cycle to oxygen, the final electron acceptor, through a series of redox reactions. In a redox reaction, one atom gains electrons or protons (reduction), and one atom loses electrons (oxidation).
•The highly electronegative oxygen acts to pull electrons through the electron transport chain.
•NAD delivers its electrons to a higher energy level in the chain than does FAD. As a result, NAD will provide more energy for ATP synthesis than does FAD.
Each NAD produces 3 ATP molecules, while each FAD produces 2 ATP molecules.