1. Cellular Respiration & Fermentation
Food as Fuel
Cellular Respiration & Fermentation

2. Harvesting stored energy
Energy is stored in organic molecules
carbohydrates, fats, proteins
Heterotrophs eat these organic molecules  food
digest organic molecules to get…
raw materials for synthesis
fuels for energy
controlled release of energy
“burning” fuels in a series of step-by-step enzyme-controlled reactions
We eat to take in the fuels to make ATP which will then be used to help us build biomolecules and grow and move and… live!
heterotrophs = “fed by others”
vs.
autotrophs = “self-feeders”

3. Harvesting stored energy
Glucose is the model
catabolism of glucose to produce ATP
glucose + oxygen  energy + water + carbon
dioxide
respiration
+ heat
C6H12O6
6O2
ATP
6H2O
6CO2  +
Remember, catabolism is the breakdown of a large molecule. By breaking down the bonds in glucose, we release energy. That energy can then be used to form ATP, which can be used in different endergonic reactions that occur in the cell.
fuel (carbohydrates)
COMBUSTION = making a lot of heat energy by burning fuels in one step
RESPIRATION = making ATP (& some heat) by burning fuels in many small steps
ATP
ATP
glucose
enzymes O2 O2
CO2 + H2O + heat
CO2 + H2O + ATP (+ heat)

4. Overview
Respiration: a way of releasing energy from food by breaking bonds of organic molecules
Aerobic respiration: requires O2; 3-step process:
Glycolysis
TCA cylce (Kreb’s Citric Acid Cycle)
Cytochrome chain (Electron Transport Chain)
Anaerobic respiration (fermentation): doesn’t require O2
Alcoholic fermentation: yields alcohol; performed by yeasts
Lactic acid fermentation: yields lactic acid; performed by muscle cells

5. Thermodynamics
1st law: Energy is neither created nor destroyed; it just changes form
2nd law: Over time, the amount of useful energy will transform into useless energy

6. Thermodynamics Exergonic reactions Endergonic reactions ∆G is negative
spontaneous
Endergonic reactions
∆G is positive

7. Thermodynamics Catalysts ∆G does NOT change
Reaction requires less activation energy and occurs faster

8. Thermodynamics
Coupled Reactions: energy released from an exergonic reaction can be used to drive an endergonic reaction.

9. Thermodynamics Coupled Reactions
This shows the nature of coupled reactions, not a true example. Notice that the energy from one event can power another.

10. Hydrolysis of ATP
The high-energy bond between the 2nd and 3rd is A LOT! Reason: the phosphate group is a bulky molecule… so when you pack them close together, it takes a lot of energy to bond them. So when ATP is hydrolyzed, all of that energy is released (∆G=-7.3 kcal/mol). It’s like stuffing luggage full of sweaters and winter jackets. Imagine stuffing it to more than maximum capacity and trying to close it. What do you think will happen when you open it? Clothes everywhere! (or maybe that just happens in cartoons, but you get the idea.)
The energy harvested from ATP hydrolysis can be used to drive endergonic reactions.

11. Phosphorylation Transfer of a phosphate group
Substrate-level phosphorylation
Oxidative phosphorylation

12. Phosphorylation
Substrate-level phosphorylation: a compound that already has a phosphate group transfers Pi onto ADP
Enzyme-mediated
Exergonic
Remember that when you go from a high-energy molecule to a lower-energy molecule, it releases energy. Therefore, exergonic!

13. Phosphorylation (substrate-level)
Phosphoenolpyruvate (PEP) forces phosphate onto ADP, making ATP

14. Phosphorylation
Oxidative phosphorylation: adding a phosphate ion directly to ADP
endergonic
The transport of just two electrons through the electron transport chain generates enough free energy in the form of electrochemical gradient to drive the synthesis of one molecule of ATP. The synthesis of ATP necessitates the dissolution of the electrochemical gradient, however, since the whole process is driven by positive hydrogen ions (protons) flowing back into the matrix space from the intermembrane space. The ETC maintains the electrochemical gradient by continuing to generate hydrogen ions.

15. Oxidation/Reduction + – + +
Oxidation: lose electrons or hydrogen atoms; exergonic
Reduction: gain electrons or hydrogen atoms; endergonic
loses e-
gains e-
oxidized
reduced + – + e- + e- e-
oxidation
reduction
redox

16. Where the electrons go, the energy goes

17. Coenzymes Chemicals that attach to enzymes to make them work
VITAMINS are coenzymes
NAD (nicotinamide adenine dinucleotide)
FAD (flavin adenine dinucleotide)
Carry the substrates to the enzymes; recycled over and over again.

18. Cofactors are chemicals that help activate proteins
Cofactors are chemicals that help activate proteins. Coenzymes are a type of cofactor.