1. Glycolysis, Kreb’s, and ETC
Cellular Respiration
Glycolysis, Kreb’s, and ETC

2. Cellular Respiration
How our body turns food and oxygen into ENERGY called ATP
Glycolysis
Kreb’s Cycle
ETC (Electron Transport Chain)

3. Redox Reactions Chemistry review: Oxidation = losing an electron
Reduction = gaining an electron
A redox reaction is a chemical reaction in which one molecule gains electrons and one loses them
Example of cellular respiration: glucose is oxidized into carbon dioxide, oxygen is reduced to water

4. Glycolysis Glycolysis is the first step of cellular respiration
It means “splitting sugar”
One molecule of glucose is split in half into 2 molecules of pyruvic acid (pyruvate)
C6H12O6  2 C3H6O3

5. Glycolysis Occurs in the cytoplasm of cells
It is a 10 step process that occurs in 2 phases
It can occur whether or not oxygen is present

6. Glycolysis Input: glucose
Output: 2 molecules of pyruvate, 2 ATP, and 2 NADH
NADH is a molecule that carries electrons from glycolysis and the Kreb’s Cycle to the ETS (it gains electrons = reduced)
Once there, it releases the electrons to make ATP (it is oxidized to NAD+)

7. Kreb’s Cycle
Step 2 of Cellular Respiration is called the Kreb’s Cycle, and is also known as the Citric Acid Cycle
It ONLY occurs in the presence of oxygen
It takes place in the mitochondrial matrix, the space between the inner folded membranes of the mitochondria

8. Kreb’s Cycle
The 2 pyruvates from glycolysis are converted to 2 molecules of acetyl coenzyme A (acetyl coA)
This enters the Kreb’s Cycle one at a time.
For each original glucose molecule, the Kreb’s Cycle will spin twice, one for each acetyl coA

9. Kreb’s Cycle
Acetyl coA undergoes a series of redox reactions in the Kreb’s cycle, rearranging its formula and transferring electrons
The net output for 2 TURNS of Kreb’s is: 6 NADH, 2 FADH2 (another electron carrier), and 2 ATP
A byproduct, carbon dioxide, is released

10. Electron Transport Chain
The last step is called the electron transport chain (ETC) or system (ETS), or oxidative phosphorylation (means losing electrons and adding a phosphate group to ADP to make ATP)
It occurs in the cristae of the mitochondria, on the membranes on the inside

11. ETC
The NADH and FADH2 molecules made in glycolysis and Kreb’s are what are used by the ETC to make ATP

12. ETC
The ETC is a series of proteins embedded in the cristae like a waterfall
NADH and FADH2 enter the highest protein, and as they “fall” down the waterfall, they pass their electrons down to more electronegative carriers
As this occurs, hydrogen ions (H+), which have lost their electrons, are pumped to the outside of the membrane

13. ETC
At the end of the chain, there is a big protein enzyme called ATP Synthase
The H+ ions flow down their concentration gradient through ATP synthase
ATP synthase spins around each time and generates enough energy to add a P to ADP, making ATP

14. ETC
As ADP is getting phosphorylized (called chemiosmosis), the electrons have reached the bottom of the waterfall
The electrons are attracted to a super electronegative atom, oxygen
Oxygen is the final electron acceptor. It gains electrons (is reduced) and joins with the H+ ions coming through ATP synthase to make water
We breathe out the water (along with the CO2 from Kreb’s)

15. ETC
At the end of the ETC, approximately 34 ATP are generated through the processes of Oxidative Phosphorylation (the electrons moving down the waterfall) and chemiosmosis (the diffusion of H+ ions through ATP synthase)

16. Summary Oxygen we breathe in becomes water
Glucose we eat is used to make ATP and CO2 (waste)
A total of approximately 38 ATP are made per glucose molecule