Microbiology Module Two: Micorbial Metabolism

Study guide answers

Embden- Meyerhof pathway (EMP) *metabolizes glucose

-glucose breakdown to pyruvate

-used in the electron transport chain

-amphibolic pathway (can run in reverse to generate glucose from pyruvate)

-energy investment during the 6-carbon phase (glucose 6-phosphate)

-NADH & substrate-level phosphorylation of ATP during the 3-carbon phase (3-phosphoglycerate)

-higher energy yield (2 ATP and 2 NADH)

-10 enzymes required-higher protein synthesis cost

PURPOSE IS TO HARVEST ENERGY

Entner-Doudoroff pathway (EDP) *metabolizes glucose

-catabolizes sugar acids and produces NADPH for biosynthesis

-primarily used by Gram-negative bacteria (soil bacteria)

-less energy yield than EMP

-less protein is used = lower protein synthesis cost

-* used when sugar acids are available instead of free glucose

• These acids go straight into central metabolism without having to be converted backwards first

PURPOSE IS TO HARVEST ENERGY

Pentose Phosphate Pathway (PPP) *metabolizes glucose

-shunts carbon from glucose into biosynthesis

-amphibolic & works within the ED pathway (no ETC occurs in the cytoplasm)

-produces NADPH in the irreversible phase (reducing power)

-produces ribose-5-phosphate in the reversible phase

-*used when a cell needs to make NADPH for chemical building blocks

or ribose-5-phosphate for DNA and RNA*

PURPOSE IS TO BUILD THINGS AND PROTECT THE CELL

Oxidative Phosphorylation

-ATP is synthesized using energy from electron transport

• In turn is driven by oxidation of a chemical source

Contains Proton Motive Force (PMF)

• Spins & generates ATP

• Drives ATP synthesis & provides energy for major cellular functions

• Protons flow down concentration gradient through ATP synthase

-oxygen not required

• Can use other electron acceptors in anaerobic conditions

-produces much ATP in Aerobic conditions

-still occurs because ETC is used, but oxygen is not the final electron acceptor; nitrate or sulfate is used in Anaerobic conditions

-fermentation does NOT use an ETC= does not occur in fermentation

Substrate-level phosphorylation (occurs primarily in glycolysis)

-generates ATP using PEP (ADP + Pi) as a source of the phosphoryl group

-Oxygen is not required

-Small amounts of ATP are produced in Aerobic conditions

-Occurs during glycolysis in Anaerobic conditions

-Essential for ATP production in Fermentation

Compare the use of ATP synthase during respiration and fermentation and discuss the role of the Proton Motive Force

Respiration

-ATP synthase produces ATP via energy stored in the proton motive force (PMF = oxidative phosphorylation)

• Fermentation does not occur during oxidative phosphorylation (doesn’t use the ETC); instead uses substrate-level phosphorylation

• ATP synthase is used during respiration

ETC length

-Longer chains and more branches mean more areas for donors to exit

-More protons pumped= more ATP

-Bacteria have shorter ETC

Anaerobic Respiration

-terminal electron acceptor is not oxygen (doesnt USE oxygen)

-provides less energy

-primary active transport is used to pump protons into the cell

Fermentation

-regenerates NAD+

-no ETC

- substrate-level phosphorylation produces ATP by glycolysis

-2 ATP for every one glucose

End products (influenced by environment)

• Lactic Acid (yogurt)

• Ethanol (Alcohol)

• Acetic acid (cheese)

• Butyric acid (acetone)

ATP synthase can run in reverse and function as a proton pump outside of cell

How substances other than glucose are catabolized

-carbohydrates are converted into monomers

-(lipase hydrolyzes) triglycerides, which are broken down into glycerol and fatty acids

• which can be shuttled into glycolytic pathways

• Fatty acids are oxidized through the beta-oxidation pathway

-Transamination

• Proteases hydrolyze protein into amino acids

• Deaminases remove amino groups from amino acids

How macromolecules (nitrogen, carbon, sulfur, and phosphorus) are assimilated by cells for biosynthesis

Nitrogen

• nitrification

• Plants associated with nitrogen fixens

Sulfur

• Elemental sulfur > biologically usable sulfur

* Reverse electron flow used to generate NADPH

Inorganic -> organic building blocks, driven by ATP and producing NADPH

Compare and contrast oxygenic photosynthesis, anoxygenic phototrophy, and rhodopsin-based phototrophy

Oxygenic photosynthesis

• Generates ATP and NADPH in one process via two photosystems

  • Photosystem Two (first electron gets light & reaction begins (P680))

    • unfavorable → favorable

    • ATP production

  • Photosystem One (P700, can work independently)

    • NADPH production

  • water as electron donor, O2 as a byproduct, fixes CO2 into sugars

• chlorophyll

• noncyclic

Anoxygenic photosynthesis

• uses sulfur and hydrogen

• water is not used as an electron source

• either uses system 1 or 2

  • uses reverse electron flow to generate NADPH using PMF

  • hydrogenase reduces NADP+ to NADPH by donating electrons from H2

  • doesn’t PRODUCE oxygen

• bacterial chlorophyll

• cyclic

Rhodopsin-based phototrophy

• absorbs light to pump a proton across the cell membrane

  • generating a PMF without an ETC

Cyclic photophosphorylation & noncyclic photophosphorylation

Cyclic

• Only ATP is made

• from light

Noncyclic

• ATP and NADPH are made

• Electrons are not cycling back through

• stops at NADPH

assimilatory nitrate reduction from dissimilatory nitrate reduction

assimilatory nitrate reduction

• Used by bacteria

• reduce nitrate

Dissimilatory nitrate reduction

• Uses NO3- as a terminal electron acceptor

*purpose is to incoporate into amino acids

assimilatory sulfate reduction from dissimilatory sulfate reduction

assimilatory sulfate reduction

• sulfate activation through formation of phosphoadenosine 5- phosphosulfate (PAPS)

• reduces to SO32- and then to H2S used to synthesis cysteine

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dissimilatory sulfate reduction

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Anabolism

-requires generation of precursor metabolites

-LPS combine lipid and carbohydrate anobolic pathways

-BUILDING