Cellular Respiration
Energy that was made in photosynthesis can be used in cellular
respiration by stripping the e- from the molecules built in
photosynthesis. The e- have extra energy from the photon that hit it.
Has 2 stages:
1. Glucose converted to pyruvate - produces small amount of ATP
*occurs in the cytosol
2. O2 present = pyruvate and NADH used to produce lots of ATP :
aerobic - needs O2
*occurs in mitochondria (eukaryotic cells); cell
membrane in cells w/o mitochondria
O2 not present = pyruvate converted to lactic acid or ethyl
alcohol : anaerobic - w/o O2
Here's the flow chart:
And the chemical reaction:
CH2O
+
O2
----------
CO2 +
H2O
+ 36ATP
Glycolysis:
*Sequence of enzyme-catalyzed rxns that converts a 6C glucose
molecule into 2, 3C molecules of pyruvate.
*This is an anaerobic reaction!!
Here's how the flow chart works:
*So at the end, we have 2- 3C pyruvates and 2ATP's
To make more ATP, there needs to be O2:
Oxidative respiration follows glycolysis when O2 is available
After glycolysis, the pyruvate molecules are converted into a 2C
fragment and a CO2 and H+ are also extracted. CO2 leaves the cell;
H+ goes to a NAD+ molecule to be used later.
The remaining 2C fragment (called an acetyl group) is attached to a
coenzyme (coenzyme A) and forms acetyl-CoA.
The acetyl-CoA gets either used in fat synthesis if there is enough
ATP or it goes to be used in the Krebs Cycle to make more ATP.
The Krebs Cycle:
This is a repeating series of rxns that produces ATP, e- carriers, and
CO2
Let's see how the cycle works!
The Krebs Cycle must turn 2x for every glucose that is converted to
pyruvate.
Electron transport chains:
*in the inner membrane of the mitochondria
*as e- pass through an e- transport chain, p+ are pumped
out of the inner chamber, the p+ build up outside and
then rush back in via ATP synthetase thus making
ATP
*at the end of each e- transport chain, H+ are added to O
forming H2O
Without O2, Fermentation occurs!
*instead of the e- getting carried away by NAD+, the eremain attached to NADH
*this takes up all available NAD+ and then glycolysis can't
continue
*SO the H+ must be attached to something else…
- in animals = H+ gets attached back to pyruvate to
form lactic acid
*this is what causes your muscles to hurt when
you work out!
- in plants = H+ gets attached to CO2 from glycolysis
to form ethyl alcohol
*this is what causes bread to rise (CO2) and beer
to become alcoholic (ethyl alcohol)
Yeast is the microorganism that performs this task!
Other fuels can be used for cellular respiration!
Glucose is not the only fuel!
Can use:
*fats
*proteins
*nucleic acids
This process can be slowed down or sped up by the demand for ATP.
How does it know when it needs to shut down?
Our friends… allosteric enzymes!!
This works exactly like any other feedback inhibition system.
Enough ATP:
Need ATP: