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AP Bio- Metabolism 3.2: Respiration
Transcript of AP Bio- Metabolism 3.2: Respiration
A Quick Recap
*-if they are present
The Citric Acid Cycle
Versatility and Regulation
Food Gives Us Energy!
There is a reciprocal relationship between chemoheterotrophic nutrition and photoautotrophic nutrition.
The inputs of one are the outputs of the other.
This explains this curious fact:
Aerobic Cellular Respiration:
C H O + 6O
6CO + 6H O
C H O + 6O
6CO + 6H O
Metabolic reactions are tightly controlled in multi-step metabolic pathways.
So that this doesn't happen:
Redox: Chemical reactions where electrons are transfered from one atom to another atom.
C H O + 6O
6CO + 6H O
Glucose will be oxidized (it is the "reducing agent").
Oxygen will be reduced (it is the "oxidizing agent").
Instead of direct transfer of electrons from glucose to oxygen, cells decouple metabolic oxidation and reduction.
compounds that store electrons from food.
Exist in oxidized and reduced forms.
In cells, electrons come with protons.
Transfer electrons and protons to other areas of the cell to continue metabolism
Two Major Kinds:
NAD+ / NADH
FAD / FADH
All respiration begins with glycolysis in the cytoplasm.
Anaerobic respiration will then require fermentation (also in the cytoplasm).
Aerobic respiration will occur in a mitochondria*. It will involve the citric acid cycle, followed by oxidative phosphorylation.
The point of all of it is to make ATP
Glucose(6C) is cleaved into 2 molecules of pyruvate (3C).
This requires 2 ATP. It produces 4.
2 NAD+ are reduced to 2 NADH
2 Phases of glycolysis
Every reaction in glycolysis is mediated by an enzyme.
Description for when ATP is produced by enzymatic phosphate transfer from another organic phosphate.
This is how ATP is produced in glycolysis and the citric acid cycle.
1 Glucose (6C)
2 Pyruvate (3C)
Glycolysis is hypothesized to be the most ancient metabolic pathway present in modern organisms.
It happens in all organisms!
Where To Next?
Make Sure You Can:
NADH is oxized back into NAD+.
This will require pyruvate to be reduced into another compound (waste product).
This enables glycolysis to keep functioning.
Hundreds of fermentation pathways. We'll look at two.
Pyruvate (3C) is converted to ethanol (2C) and a molecule of CO (1C)
Example Organism: Yeast
Lactic Acid Fermentation:
Pyruvate (3C) is converted to lactate (3C)
Example Organism: All Animals (muscle cells)
Ethanol fermentation is possibly the most commercially lucrative biological reaction.
2 Pyruvate (3C)
Various Carbon Waste Products
Following glycolysis, aerobic respiration in eukaryotes will take place in the mitochondrion.
The products of glycolysis are transported through both mitochondrial membranes into the mitochondrial matrix.
This is where the citric acid cycle occurs.
Prokaryotes that carry out aerobic respiration utilize specialized portions of their cell membrane.
While being transported in to the mitochondrion, pyruvate is converted into an acetyl group (-CH CH ) and a molecule of CO
The CO is a waste product.
The acetyl group is attached to a moleule of CoEnzyme-A (CoA). This is the carbon input into the citric acid cycle.
Another NAD+ is reduced to NADH
The acetyl group from pyruvate is attatched to oxaloacetate, forming citric acid (aka "citrate")
The carbons from the acetyl group are oxidized into 2 CO .
3 molecules of NAD+ are reduced into NADH
1 molecule of FAD is reduced into FADH
1 ATP is produced
The citrate is converted back in to oxaloacetate.
Remember: This cycle happens 2X per glucose.
Every reaction in the citric acid cycle is mediated by an enzyme.
1 Acetyl-CoA (2C from pyruvate
1 Pyruvate (3C)
1 Acetyl-CoA (2C from pyruvate)
The Citric Acid Cycle was discovered by Hans Krebs, who won a Nobel Prize for his efforts in 1953.
It's also widely known as the "Krebs Cycle".
X 2 per glucose
X 2 per glucose
The reduced electron shuttles (NADH and FADH ) are oxidized at the "electron transport chain" (ETC): complexes of proteins embedded in the folds of the inner mitochondrial membrane ("cristae").
Electrons flow through the proteins in the chain, driven by the increasing electronegativity of the members of the ETC.
As the electrons move through the chain, the free energy they release is used to pump protons (H+) through the ETC proteins from the matrix into the intermembrane space.
Oxygen serves as the "terminal electron acceptor". When O acquires 4 electrons and 2 protons, it is converted into water, which is released as a waste product.
The oxidized electron carriers are fed back into glycolysis, and the citric acid cycle.
How ATP is produced.
The ETC establishes a proton (aka "electrochemical") gradient.
Protons can only diffuse back in to the matrix through a protein channel.
ATP synthase: The only proton channel available in the inner membrane.
As protons diffuse through ATP synthase, the free energy that is released is used to catalyze ATP formation from ADP and free phosphate groups ("oxidative phosphorylation")
Chemiosmosis was proposed by Peter Mitchell, who won a Nobel Prize for his efforts in 1978.
It is the major mechanism by which ATP is produced in aerobic cellular respiration AND photosynthesis.
Why it's impossible to get a straight answer
A natural question:
How much ATP is produced per glucose?
Can't be answered any more exactly than something like "32-36".
Decoupling of glucose oxidation and oxidative phosphorylation.
3 ATP per NADH
2 ATP per FADH
Anaerobic < Aerobic
If we consider a hypothetical maximum of 38 ATP per glucose molecule, aerobic cellular respiration is 19X more efficient than anaerobic cellular respiration in terms of usable energy generated.
Aerobic In Depth
Aerobic cellular respiration is ~40% efficient in terms of converting chemical energy in glucose into chemical energy in ATP.
By comparison, your car is ~15% efficient at converting the chemical energy in gasoline into mechanical energy.
How do living systems process energy?
This chimpanzee would die if it didn't eat. You don't want a chimpanzee to die, do you? DO YOU?!?!?
While we focus on Glucose....
...you should be aware that all macromolecules can be used as substrates for respiration.
Different components will enter the process at different points.
If an animal is starving, the following order of digestion of stored molecules will occur:
Carbohydrates (3 days)
Fats (~3 weeks)
Proteins (only at the very end)
So many control points:
Since every step of respiration is mediated by enzymes, there are multiple opportunities for feedback to control the process.
Phosphofructokinase (a glycolysis enzyme) is a particularly studied control point. It is stimulated by AMP, and inhibited by ATP and citrate.
* eukaryotes only
Rest in Peep!
Explain how chemoheterotrophic energy processing allows for the production of useful energy for organisms.
Explain why and how chemoheterotrophic energy processing is controlled.
Identify the reduction and oxidation reactions that occur in cellular respiration.
Explain the processes and identify all inputs and outputs of all steps of anaerobic and aerobic cellular respiration.
Relate the different steps of chemoheterotrophic nutrition to their locations in the cell.
In Glorious Computer Animation
Organic Molecules (ex. glucose)
Respiration is catabolic and exergonic.
On to the next one.