Topic 5: Organotrophy Flashcards
What is Aerobic Respiration?
- A combustion reaction, where glucose is burned to produce Co2, H2) and energy
- A series of coupled redox reactions, releasing the free energy of glucose and transfers some of the released energy to other molecules
In Aerobic Respiration what is being oxidized?
The Carbon atoms in glucose are oxidized to form CO2
In Aerobic Respiration what is being reduced?
The O2 atoms in the reactants are being reduced to form water
Redox potential generated from biological redox reactions is stored in?
Electron Carriers
What are Electron Carriers?
Energy transport molecules the move electrons from one reaction to another
What is the first step of Cellular Respiration?
Glycolysis
What is Glycolysis?
Occurs in the cytosol
Inputs: 1 glucose (6C), 2 NAD+
Outputs: 2 Pyruvate (3C), 2 NADH
- Consumed 2 molecules of ATP and produced 4 molecules of ATP (formed by substrate-level phosphorylation)
- NAD+ is reduced
- Pyruvate has a lot of potential energy
What is the main goal of glycolysis?
To breakdown one molecule of glucose into 2 pyruvate (producing NADH and ATP in the process)
Electron carriers normally…
Reduced, gaining electrons
e.g.
NAD+ in glycolysis
What is Substrate-Level Phosphorylation?
When an enzyme catalyzes the transfer of a phosphate from a phosphorylated organic molecule to ADP to make ATP (occurs in glycolysis to produce ATP)
Why is glycolysis only partial glucose oxidation?
- Not much ATP has been made
- The cell needs to remove pyruvate (the final product should not build up in the cell)
- The cell needs to restore NAD+ (through oxidizing NADH)
What is the energy investment phase in glycolysis?
When 2 ATP molecules are used to add phosphate groups to glucose
What is the pay-off phase in glycolysis?
When 4 ATP molecules are made through substrate-level phosphorylation and 2 NADH molecules are made through oxidizing NAD+
What is fermentation?
The anaerobic (no or limited oxygen) reduction of Pyruvate
What happens after glycolysis if O2 is available?
Pyruvate Oxidation
What happens after glycolysis if O2 is not available?
Fermentation
Where does fermentation occur?
Cytosol
What is the main goal of fermentation?
To oxidize NADH to NAD+, so it can allow glycolysis to continue
What are the two kinds of fermentation?
Lactate fermentation and Alcoholic fermentation
What is Lactate fermentation?
- The reduction of pyruvate to produce a lactate, which is coupled to the oxidation reaction of NADH and H+ to form NAD+
- This allows glycolysis to continue; indirectly making ATP
What is Alcoholic fermentation?
- The decarboxylation of pyruvate (releasing CO2), forms Acetaldehyde which is reduced to an alcohol, which is coupled to the oxidation reaction of NADH and H+ to form NAD+
- This allows glycolysis to continue; indirectly making ATP
What is pyruvate oxidation?
- It occurs in the mitochondrial matrix
- Connects glycolysis to the Kreb Cycle
Input: 2 Pyruvate (3C), 2 NAD+, CoA (coenzyme)
Output: 2 AcetylCoA (2C), 2 NADH, 2CO2 - Pyruvate undergoes decarboxylation releasing CO2, then undergoes oxidation produce Acetyl Group
- The oxidation reaction is coupled to the reduction of NAD+ to produce NADH and H+
- Lose 2 C overall
What is the main goal of the Krebs (Citric Acid) Cycle?
To finish the oxidation of glucose to CO2
What is the Kreb Cycle?
Input: Acetyl CoA (2C), 3NAD+, ADP, FAD
Output: 2CO2, 3NADH, ATP, FADH2
- First, oxalacetate (4C) combines with Acetyl CoA, to form citrate (6C)
- Citrate undergoes decarboxylation which releases 2CO2, then NAD+ is oxidized to make NADH, then ATP is restored through substrate-level phosphorylation, and lastly, FAD is reduced to form FADH
The Kreb cycle is not just glucose…
- Other fuel sources are broken down and can enter pathways
- Intermediates can be used in anabolic pathways
What is the Electron Transport Chain (ETC)
- A series of proteins in the inner mitochondrial membrane that helps cells make energy
- Electron flow is coupled to pumping H+ from the matrix to the IMS to generate an electrochemical gradient
What are the layers of the mitochondrial membrane?
- Outer mitochondrial membrane
- Inner membrane compartment
- Inner mitochondrial membrane
- Mitochondrial matrix
How is electron flow REDOX driven?
- Electrons flow to increasingly more electronegative prosthetic groups until they reach the final electron acceptor, O2
- With each electron transfer, the electron moves closer to the atomic nucleus
- Free energy is released
What is a prosthetic group in the ETC?
Associated with protons but not made of amino acids
What is the free energy released in ETC used for?
Free energy that is released is used to do work (pump H+ across the membrane; ultimately used to produce ATP)
What do Complex I and II do?
- NADH in the mitochondria matrix donates electrons (reduces) Complex I
- H+ is pumped from the matrix to IMS by Complex I
- FADH2 in the matrix donates electrons to Complex II only (not enough energy to drop electrons in Complex I)
What does Ubiquinone (UQ) do?
- A hydrophobic electron taxi
1. Taxis electrons from Complex I to Complex III
2. Taxis electrons Complex II to Complex III
3. When UQ is reduced it takes up a proton from the matrix, when UQ is oxidized it releases protons in the IMS
What do Complex III, Cytochrome C, and Complex IV do?
- Electrons will flow from Complex III to the taxi Cytochrome C
- Cytochrome C is a hydrophilic protein taxi that moves electrons from Complex III to IV
- Electrons flow through Complex IV to O2, which is reduced to form water
- H+ is pumped from the matrix into the IMS by Complex IV
How is [H+] lowered in the matrix?
- Pumped protons across the membrane
- Used to reduce oxygen into H2O
What is Proton Motive Force?
The H+ electrochemical gradient
What is the Proton Motive Force used for?
- Chemiosmosis
- PE of the PMF is used to power ATP Synthase
- Moves H+ through the enzyme ATP Synthase back into the matrix, which powers the synthesis of ATP from ADP and Pi (using Oxidative Phosphorylation)
What is Oxidative Phosphorylation?
Energy in the PMF, generated by the ETC is used to make ATP
What is ATP Synthase?
As protons flow through the channel (Fo), rotate and the energy is used to drive the catalytic part
ATP yields in Aerobic Respiration?
Total is ~ 32 ATP, but can be as high as 38
Why do ATP yields vary in Aerobic Respiration?
- Some PMF is used for other purposes
- NADH and FADH2 can be used for other reactions
If we don’t need ATP what can be stored as?
- Glucose can be stored as a polymer (glycogen in animals or starch in plants)
- Triglycerides for longer-term storage
*Can be reversed
How does Aerobic Respiration work in Prokaryotes?
- Don’t have membrane-bound organelles, therefore all metabolisms occur in the cytosol and on the cell membrane (other than that, its the same)
Intermediates from Glycolysis or Kreb Cycle can be…
- Used to build biomolecules (source of carbons)
- Carbon is needed for macromolecules (amino acids, proteins, nucleic acid, lipids)
- Acetyl CoA can be used to generate macromolecules (instead of going through Krebs Cycle), a building block to make fatty acids
