BIOL 241: Topic 5 - Organotrophy

C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy

What is the overall reaction formula for aerobic respiration?

• Series of coupled redox reactions that release the free energy of glucose and transfer some of it to other molecules.

What is aerobic respiration?

• Non-polar covalent bonds in the reactants (C-C, C-H, O=O).

What bonds are broken during cellular respiration?

• Polar covalent bonds in the products (C=O, O-H).

What bonds are formed during cellular respiration?

• Glucose is oxidized and it becomes 6CO2 since the electrons from the carbon atoms in glucose move further away from the C atoms.

What reactant in cellular respiration is oxidized? What is the product?

• 6O2 is reduced and it becomes 6H2O since electrons between the energy atoms in O2 move closer to the O atoms.

What reactant in cellular respiration is reduced? What is the product?

• Reduction potential.

What do biological redox reactions generate?

• In electron carriers (NADH, FADH2, NADPH).

Where is reduction potential stored?

• They transfer potential energy from one molecule to another.

What do electron carriers do?

Reactants: Glucose (6C) + 2NAD+ + 2ADP + 2 Pi

Products: 2 Pyruvate (3C) + 2ATP + 2NADH

What are the reactants and products of glycolysis?

• Yes, since most of the energy from glucose goes to pyruvate.

Does pyruvate have a lot of energy?

• So that it doesn't build up and cause a great concentration of pyruvate.

Why does the cell need to remove pyruvate after glycolysis?

• Must be oxidized to NADH since NAD+ is very costly for the cell to make.

How does the cell restore NAD+?

• Pyruvate must enter a fermentation pathway.

What do eukaryotic and prokaryotic organisms do if oxygen is limited?

• Pyruvate is reduced by NADH + H+ to form lactic acid or ethyl alcohol; they both produce 2 ATP.

What happens to pyruvate in fermentation?

• Lactate Fermentation.

What type of fermentation do multicellular organisms undergo?

• Alcohol Fermentation.

What type of fermentation do single-celled organisms undergo?

• Mitochondrial matrix.

Where do eukaryotes oxidize pyruvate?

• Pyruvate is oxidized into Acetyl CoA (2 carbon molecule attached to an enzyme (A)).
• CO2 (due to a carboxyl group being removed and releasing CO2).
• NADH (reduced from NAD+).

(This is x2 since two pyruvates are made from one glucose).

What is pyruvate oxidized into? What other molecules are produced?

• 4 CO2
• 6NADH
• 2FADH2
• 2 ATP

What is produced at the end of the Krebs Cycle (per glucose)? (4)

• Amino acids.
• Fatty acids.
• Nucleic acids.

What can pyruvate be made from? (3)

• REDOX reactions.

What is electron flow driven by?

• Through electron flow and pumping hydrogen ions from the matrix into the intermembrane space. This is important since this process creates potential energy used to make ATP.

How does the ETC create an electrochemical gradient? Why is this important?

• NADH in the matrix is reduced and donates electrons to complex I.
• Complex I uses ATP to pump hydrogen ions into the intermembrane space.
• FADH2 from the matrix is reduced and donates electrons to complex II; no hydrogen ions are pumped.

What happens at complexes I and II (in the ETC)? (3)

(Hint: What happens to NADH and FADH2?)

• It taxis electrons from CI (complex I) and CII (complex II), and from CII to CIII (complex III).
• When its reduced, UQ takes hydrogen ions from the matrix and delivers it to the intermembrane space when oxidized.

What does ubiquinone (UQ) do? (2)

• Electrons flow from CIII to CIV (via cytochrome c).
• Hydrogen ions are pumped from the matrix into the IMS by CIII.
• CIV delivers electrons to the final electron acceptor (O2).

What happens at CIII (complex III) and CIV (complex IV)? (3)

• Taxis electrons from CIII to CIV.

What does Cytochrome C do?

• When hydrogen ions are pumped across the IM (inner membrane), and when hydrogen ions are used to reduce oxygen to water.

When is the concentration of hydrogen ions lowered in the matrix?

• The proton motive force.

What is the hydrogen ion electrochemical gradient called?

• The gradient that reflects the hydrogen ion difference across the inner membrane.

What is the Proton Motive Force?

• The IMS's pH (pH = 5) is 100x higher than in the matrix (pH = 7).

Where is pH higher: in the intermembrane space, or in the matrix?

• Used for chemiomosis.
• Uses the potential energy of the proton motive force to power ATP synthesis. As H+ ions move down their gradient, enough free energy is released to phosphate ADP to ATP.

What is the proton motive force used for? How does it perform its function? (2)

(Hint: ADP and ATP)

• Approximately 32 ATP, could be as high as 38 ATP.

About how much ATP is produced in aerobic respiration?

• Some NADH/FADH2 is used for other reactions since the proton motive force is not only used for ATP synthase, but also for pyruvate transport into the mitochondria. Additionally, it could be used for things such as fermentation.

Why does the number of ATP produced vary?

(Hint: think about glycolysis and other processes related)

• As a polymer (glycogen in animals, and starch in plants).
• Triglycerides can also be generated for longer-term storage.

If ATP isn't needed, how can glucose be stored? (2)

• Amino acids, nucleic acids, and lipids.

What can Acetyl-CoA be used to generate?

• Metabolism occurs in the cytosol and on the cell membrane.
• Yes, the process of aerobic respiration is the same aside from where the process occurs.

Due to prokaryotic organisms not having membrane-bound organelles (no mitochondria), where does metabolism occur? Additionally, is aerobic respiration the same in eukaryotic and prokaryotic organisms?

• A form of respiration that only occurs in prokaryotes. This is respiration without the use of oxygen as the final electron acceptor, but rather uses other electron acceptors such as SO4 and NO3.

What is anaerobic respiration?

• It is the oxidation of inorganic compounds that only occurs in prokaryotes. It primarily uses initial electron donors such as H2S, FE3+, H2, and NH3 and not FADH2 or NADH. This process does NOT require glycolysis, pyruvate oxidation, or the Krebs Cycle. However, it does require ETC and oxidative phosphorylation.

What is Chemolithotrophy?

(Hint: Does it occur in eukaryotes? Does it use the same electron donors as eukaryotes do? Which processes does it require and not require?)

• No, since using different primary electron donors/acceptors generates proton gradients of different strengths. Additionally, organic electron donors store more potential energy than inorganic electron donors, therefore, they generate a stronger proton gradient than all other donors. Lastly, oxygen is a stronger final electron acceptor than all other acceptors, resulting in a stronger PMF.

Are all types of metabolic pathways equal?

(Hint: Think about the various electron donors and acceptors, if organic or inorganic electron donors are stronger, and the type of final electron acceptor used.)

• ATP
• NADH
• H2O
• CO2

What molecules is the free energy of glucose released to? (4)

• Cytosol.

Where does glycolysis occur?

• A partial oxidation of glucose, which results from the breakdown of glucose by various enzymes, and releases ATP and pyruvic acid.

What is glycolysis?

• Substrate-Level Phosphorylation.

What is ATP generated by?

• Metabolism reaction that results in the production of ATP by the transfer of a phosphate group from a substrate directly to ADP.

What is substrate-level phosphorylation?

• Pyruvate Oxidation.
• Citric Acid Cycle.

What occurs in the matrix? (2)

• Inside the mitochondrial membrane and intermembrane.

Where is the matrix located?

• Electron Transfer.
• ATP Synthesis by ATP synthase.

What occurs in the inner mitochondrial membrane? (2)

• Secondary Active Symport.

What type of transport occurs when pyruvate is transported into the mitochondrial matrix?

• Krebs Cycle.

What is the citric acid cycle known as?

• 8 connected reactions.
• 8 enzymes.

How many connected reactions and enzymes are there in the Krebs Cycle?

• There are 4 protein complexes (I,II,III,IV)
• They are embedded in the inner membrane.

How many protein complexes are there and where are they embedded? (2)

• No, it is not very efficient since hydrogen ions can be pumped away.

Is Chemolithotrophy efficient? Why or why not?

• Aerobic respiration due to the most ATP being used per electron donor and final electron acceptor.

What type of respiration has the highest PMF?

• Anaerobic respiration due to it using the best donors, but them not being as good as the final electron acceptor. There is less ATP used per electron donor.

What type of respiration has the second highest PMF?

• Chemolithotrophy since it has the worst donor and rarely uses O2 as a final electron acceptor. This is the least ATP used per electron donor.

What type of respiration has the lowest PMF?

• Aerobic
• Anaerobic
• Chemolithtrophy

What are the three main types of respiration?