Ch. 9 Cellular Respiration Harvesting Chemical Energy. 9.1 Catabolic pathways yield energy by oxidizing organic fuels. Energy flows into an ecosystem as sunlight and ultimately leaves as heat, while the chemical elements essential to life are recylcled .
Energy flows into an ecosystem as sunlight and ultimately leaves as heat, while the chemical elements essential to life are recylcled.
The coupled reactions are what keeps all life connected.
6CO2 + 6H2O ------- C6 H12 O6 +6 O2
C6 H12 O6 + O2-----6CO2 +6H20+ATP
The products of one reaction become the reactants of the next
Energy Must be transferred .
For every e- that is lost by one atom that same e- must be gained by another atom.
X is the reducing agent because it donates the electron.
Y is the oxidixing agent because it accepts the electron.
One cannot exist without the other.
The Empty Bus. NAD+ will combine with 2e- and 2H+ ( donated by food) to create NADH (the loaded bus) and a free H+
This energy rich molecule will shuttle e- and H+ from glycolysis and the citric acid cycle to oxidative phosphorylation..
a.) Uncontrolled fall of electrons
Too muck energy at once, No control, boom!
b.) Cell Respiration -Key differences :
1st - the H that reacts with O is derived from food rather than H2.
2nd- Cell respiration uses the ETC to break the fall of electrons into several Energy releasing steps
c.) How it works: Electrons removed from food are shuttled by NADH to the “top” of the high energy end of the chain. At the “bottom”, lower-energy end oxygen captures these electrons along with H+ , forming water.
2 ways to make ATP
1. substrate level phos. (not very efficient) but makes a lot of loaded buses.
2. Oxidative phos. Very efficient but requires O2
Happens in Glycolysis and the Kreb Cycle
An enzyme acts on a substrate, breaking off a phosphate and giving it to ADP to make ATP.
10 step process takes place in the cytosol
Net Product of 2 ATP. 4 ATP are formed but 2 ATP are consumed.
Pyruvate is the branching point:
No 02 = Fermentaion
O2 Present= Cell Respiration
The conversion of pyruvate to acetyl CoA, the junction between glycolysis and the cytric acid cycle.
To calculate the inputs and the outputs on a per-glucose basis, multiply by 2, because each glucose molecule is split during glycolysis into two pyruvate molecules
AKA Kreb Cycle.
In Mitochondial Matrix
Produces Small amount of ATP (2)
Produces Large Amount of Electron carriers, NADH (8) and FAD2 (2)
The controlled fall of Electrons
1,000 of ETC are embedded in the cristae of the inner mitochondrial membrane.
Most components are proteins.
The ETC carriers shift between reduced and oxidized states as the donate and accept electrons.
The Players: The e- are transferred from NADH, Flavoprotein, Complex I, to Q, to a series of cytochromes, and finally to Oxygen. Which picks up to H+ and forms water.
It is hot potato with a finishing splash of H20.\
Note : FADH2 adds its electrons at a lower level , thus FADH2 provides 1/3 less the energy to make ATP
ATP Synthase, a molecular mill:
Protein uses the energy of the proton (H +) Gradient to make ATP.
The proton gradient is produced as members of the ETC pass electrons, while passing e- they also accept and release H+.
The concentration of H+ builds up in the intermembrane space. This gradient stores potential E referred to as the “Protomovtive force”.
The flow of H+ down the gradient through the rotor and stator part of the ATP synthase cause the rotor and attached rod to rotate, activating the catalytic sites on the knob portion where ADP and iP join to form ATP.
It’s the “Bump”
The proton gradient is produced as members of the ETC pass electrons:
while passing e- they also accept and pump H+ across the membrane into the intermembrane space.
The Big Picture
Why 36 or 38 and not a discreet number?
Because it depends on which shuttle transports the e- from NADH in the cytosol to the ETC.
If it is FADH2 =less ATP
If it is NADH= more ATP
a. Alcohol Fermentation
Consists of glycolysis plus reactions that regenerate NAD+ by transferring e-’s from the NADH molecules to pyruvate.
When pyruvate picks up (accepts) the 2 H+’s it becomes Ethanol.
Lactic Acid Fermentation
Pyruvate is reduced by NADH with no release of CO2.
Human muscle cells make ATP this way when O2 is scarce.
This occurs during the early stages of strenuous exercise when sugar catabolism outpaces the muscles supply of O2 from the blood.
The cells switch from aerobic respiration to anaerobic. Lactate builds up causes fatigue and pain. But is carried to the liver to be converted back to pyruvate.
Pyruvate as the key junction in catabolism.
Glycolysis is common to Fermentation and Cell Respiration.
The product of Glycolysis, pyruvate, represent the fork in catabolic pathways.
The catabolism of various molecules from food:
“Love the one your with”
Any for these 3 macromolecules can be used a fuel source to create ATP. Proteins and Fats just need to be altered first.
Proteins- to AA then AA are further broken down in a process called deamination when the – NH2 group is broken off. This will increase the nitrogenous waste.
Fats-great fuel source. 1 g. of fat produces twice the amount of ATP than 1g. of Carb. But requires a lot of intermediate steps. That’s why you have to work so hard to lose weight. Longer process to break down fats.
Feedback Inhibition controls the anabolic and catabolic pathways.
Phosphofructokinase- pace maker of respiration. It is an allosteric enzymes with Receptor sites fro AMP and ATP.
ATP binds to Phospho. and respiration is inhibited.
AMP binds to Phospo. and the respiration isstimulated.
Cells are thrifty,expedient and responsive to their metabolism.