Microbial Metabolism and Growth

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Questions and Answers

What is the primary role of catabolism in metabolism?

Biosynthesis of molecules

Cell growth and development

Transport of nutrients

Energy generation (correct)

In redox reactions, what does the term 'electron donor' refer to?

The substance that gains electrons

The molecule that is oxidized

The final product of the reaction

The substance that loses electrons (correct)

Which of the following shows the correct oxidation and reduction processes in the overall reaction involving H2 and O2?

Oxidation: O2 → O-, Reduction: H2 + e- → H+

Oxidation: H2 → H2O, Reduction: O2 + 2e- → O-

Oxidation: O- → O2 + 2e-, Reduction: H2 → H2O

Oxidation: H2 → 2H+ + 2e-, Reduction: ½ O2 + 2H+ + 2e- → H2O (correct)

What is essential for both energy generation and biosynthesis in cellular metabolism?

High energy phosphate bonds and reducing equivalents Signup and view all the answers

Which classification describes organisms that obtain energy from organic compounds and carbon from CO2?

Chemoautotrophs Signup and view all the answers

In balancing redox reactions, which element is typically balanced last?

Hydrogen Signup and view all the answers

What is the role of proton motive force in cells?

To generate ATP through ATP synthase Signup and view all the answers

What is the oxidizing agent in the oxidation of iron (II) to iron (III) with molecular oxygen?

O2 Signup and view all the answers

What is the primary method of ATP generation during substrate level phosphorylation?

Transfer of phosphate from a substrate to ADP Signup and view all the answers

Which reaction represents the overall cellular respiration equation?

C6H12O6 + 6O2 → 6H2O + 6CO2 Signup and view all the answers

What is the role of electron donors in redox reactions?

To donate electrons and become reduced Signup and view all the answers

In redox reactions, what does a more positive reduction potential indicate?

A higher tendency to accept electrons Signup and view all the answers

How is energy released when electrons move down the electrochemical gradient?

By increasing potential difference between donor and acceptor Signup and view all the answers

Which compound is typically used as an electron acceptor in aerobic respiration?

Oxygen (O2) Signup and view all the answers

What is a common challenge faced during fermentation processes?

Accumulation of reducing agents Signup and view all the answers

What does the ΔG' represent in the context of redox reactions?

Free energy change of the reaction Signup and view all the answers

What defines substrate level phosphorylation?

ATP production directly from substrate conversion Signup and view all the answers

Which of the following correctly describes the oxidation state of carbon in glucose?

-4 Signup and view all the answers

What is the primary purpose of ATPase in cellular processes?

To generate ATP from ADP and Pi using an ion gradient Signup and view all the answers

Which of the following reactions represents a reduction process?

C3H4O3 + 2H+ + 2e- → C3H6O3 Signup and view all the answers

How do microbes generate ATP when a H+ gradient is not feasible?

By utilizing an Na+ gradient instead Signup and view all the answers

What is the electron donor during anaerobic respiration when nitrate is the electron acceptor?

Glucose Signup and view all the answers

Which process generates the highest amount of energy when using O2 as the electron acceptor?

Aerobic respiration Signup and view all the answers

What type of photosynthesis involves e- derived from H2S, Fe2+, or organic acids?

Anoxygenic photosynthesis Signup and view all the answers

Which enzyme is involved in converting hydrogen peroxide into water and oxygen?

Catalase Signup and view all the answers

In what way does the light affect chlorophyll during photosynthesis?

It activates electrons making them more negative Signup and view all the answers

What type of gradient is essential for the function of ATPase?

H+ ion gradient Signup and view all the answers

Which of the following is NOT a characteristic of scalar reactions?

They involve external electron donors Signup and view all the answers

Study Notes

Metabolism

Metabolism is the sum of all chemical processes within a living system.
Catabolism breaks down molecules and releases energy.
Anabolism builds up molecules and requires energy.

Cellular Requirements for Growth

Cells require major and minor elements (like carbon, nitrogen, sulfur), water, energy from redox reactions, and reducing equivalents (e.g., NADH, NADPH) for growth.
Approximately half of E. coli's genes are involved in metabolism.

Energy and Carbon Source Classification

Microbes are classified based on their energy and carbon source.
- Chemo - energy from chemical compounds
- Photo - energy from light
- Organo - carbon from organic compounds
- Litho - carbon from inorganic compounds
- Hetero - carbon from organic compounds
- Auto - carbon from inorganic compounds

Life is Redox

Free energy change (ΔG) determines the spontaneity of reactions:
- ΔG < 0: exergonic, releases energy
- ΔG > 0: endergonic, requires energy
Standard conditions are denoted by a superscript 𐩑 and prime (') indicates pH = 7.

Redox Reactions

Oxidation: loss of electrons (electron donor)
Reduction: gain of electrons (electron acceptor)
Balancing redox reactions:
- Balance carbon to carbon dioxide.
- Balance other elements.
- Use water to balance oxygen.
- Use hydrogen ions (H+) to balance hydrogen.
- Use electrons (e-) to balance charges.

Redox Potential

Reduction potential: tendency of a compound to become oxidized or reduced, measured in volts (V).
The more positive the reduction potential (E𐩑’), the better the compound accepts electrons.

Proton Motive Force/Electron Transport

Electron transport chains generate a proton gradient (proton motive force).
The greater the difference in redox potential between the electron acceptor and donor, the greater the energy released.
ΔE’ = E𐩑’ acceptor - E𐩑’ donor
ΔG𐩑’ = -nFΔE𐩑’
- n: number of electrons transferred
- F: Faraday Constant

ATP Generation

ATP is the primary energy currency of cells.
Two main mechanisms for ATP generation:
- Substrate-level phosphorylation (SLP): direct transfer of a phosphate group from a substrate to ADP.
- Transmembrane ion gradient: movement of ions across a membrane, often coupled to electron transport.

Fermentation

ATP is produced by SLP.
The substrate serves as both electron donor and acceptor, resulting in no net change in oxidation state.
Fermentation relies on organic molecules as electron acceptors, unlike respiration, which uses inorganic acceptors like oxygen.
Fermentation products vary depending on the starting substrate and the microbial organism.

Substrate-Level Phosphorylation

A phosphorylated substrate is oxidized, releasing energy to form a high-energy phosphate bond.
This energy is then transferred to ADP to produce ATP.
All steps can occur in one reaction.

ATP Synthesis by ATPase

ATPase is a protein complex that uses ion gradients to synthesize ATP.
- F0 subunit: hydrophobic, spans the membrane.
- F1 subunit: hydrophilic, located on the interior surface of the membrane, catalyzes ATP synthesis.
3-4 protons are transported per ATP molecule.
ATPase functions are reversible.

Transmembrane Ion Gradients

Ion gradients are generated via the proton motive force, which is used by ATPase and other processes.
In environments where proton gradients are not feasible (high pH), microbes can use sodium (Na+) gradients.
Importance of ion gradients:
- ATP generation
- Flagella rotation
- Ion-coupled transport
- Maintaining turgor pressure
- Maintaining pH
- NAD+ → NADH regeneration via reverse electron flow

Generating Ion Gradients via Respiration

Electron transport across the cytoplasmic membrane generates an electrochemical gradient, driving proton export.
Electron carriers can be specific for electrons or for both electrons and hydrogen ions (reducing equivalents).
Oxygen as an electron acceptor yields the highest energy output but produces toxic byproducts like hydrogen peroxide and superoxide radicals.

Microbial Fuel Cells

Electrodes act directly as electron acceptors, bypassing electron transport chain steps.

Generating Ion Gradients via Photosynthesis

Occurs in a limited number of bacterial lineages (e.g., Cyanobacteria).
Light transfers energy to chlorophyll molecules, making them strong electron donors.
Chlorophyll absorbs light energy, enabling a flow of electrons down an electrochemical gradient.
Chlorophyll and associated proteins and pigments form the reaction center, where electron changes occur.
Antenna pigments collect light energy to funnel to the reaction center.

Types of Photosynthesis

Cyclic: electrons flow from activated chlorophyll and back to the chlorophyll, primarily generating ATP.
Noncyclic:
- Anoxygenic: electrons come from H2S, Fe2+, or organic acids.
- Oxygenic: electrons come from water (electron donor), occurs only in cyanobacteria.

Generating Ion Gradients via Enzyme Pumps

Specific pumps, like bacteriorhodopsin, directly transport ions across the membrane without relying on electron transport chains.

Generating Ion Gradients via Scalar Reactions

Reactions involve the production of protons internally, contributing to the proton gradient without directly transporting ions.
Example: oxalate decarboxylase (oxalate + H+ → formate + CO2).
Scalar reactions are not directly coupled to electron transport or light energy.

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Description

Explore the fascinating world of metabolism in microbes, including the distinction between catabolism and anabolism. This quiz covers cellular requirements for growth, energy classification, and the significance of redox reactions in microbial life. Test your understanding of how organisms harness energy and matter for their survival.