Major Points
1. Glycolysis: no O2-low ATP yield-cytoplasmic
2. Krebs cycle: O2-ow ATP yield-high NADH/FADH2 yield-mitochondrial
3. Electron transport phosphorylation: O2-high ATP yield-mitochondrial
Energy Releasing Mechanisms
* Aerobic respiration
- Respiration, from Latin "to breathe"
- Breakdown of carbohydrates to CO2 + H2O
- O2 --> ultimate electron acceptor
- High yield of energy (as ATP)
Energy Releasing Mechanisms
* Fermentation
- Bacteria, yeast, and anaerobic muscles
- In the absence of O2
- Very low yield of energy
* Nonaerobic electron transport
- Bacteria
- Final electron acceptor not O2
- Lower energy yield than in aerobic respiration
Glycolysis
* ATP is generated by substrate-level phosphorylation
- Transfer of phosphate from substrate to ADP to form ATP
* Requires formation of phosphorylated carbohydrate without using ATP
Glycolysis
* Formula:
Glucose + 2ADP + 2Pi + 2NAD+ ---> Pyruvate + 2ATP + 2NADH + 2H2O
Glycolysis
* 6-carbon unit (glucose) --> Two 3-carbon units (pyruvate)
* Glucose has more energy than pyruvate
so Where does the energy go?
* Some is converted to 2ATP and 2NADH
Aerobic Respiration
* Occurs in the mitochondrion
* Has two stages:
- Krebs cycle
- Electron transport phosphorylation
Krebs Cycle
* Pyruvate is converted to CO2 and H2O
* Only 2ATP are derived directly by substrate-level phosphorylation
* Most of the energy released as 8NADH and 2 FADH2
Electron Transport Phosphorylation
* The electrons carried on NADH and FADH2 are passed down an electron transport
chain
* As they pass protons are pumped across an internal mitochondrial membrane
* Using the gradient set up, protons pass back across the membrane as ATP
is generated
Balance Sheet of Aerobic Respiration
Glycolysis 2 ATP
from NADH 4 ATP
Krebs Cycle 2 ATP
E. T. P.
from NADH 24 ATP
from FADH 4 ATP
_______
TOTAL 36 ATP
Anaerobic Respiration
* Lactate fermentation
- Occurs in bacteria (Lactobaccilus)
- Occurs in muscles
* Ethanolic fermentation
- Occurs in yeast
* Both recover the NAD+ consumed in glycolysis to allow continued ATP production