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Flashcards in CH 11 microbial metabolism Deck (51):


-Catabolic rxns--break down complex molecules to simpler compounds, release E, supply e- (reducing power), provide materials for biosyn. (recycle)
-anabolic rxns--build complex molecules from simpler compounds, uses E


ATP: Energy Currency

-ATP is formed as a result of catabolic rxns
-ATP is used to drive anabolic rxns

-Has high E phosphate bounds, transfers phosphate to other molecules (high group transfer potential)

-Syn. by phosphorylation of ADP (AMP signals E defecit, produce more ATP)--substrate-level phosphorylation, oxidative phosphorylation (respiration), photophosphoylation (photosynthesis)


Oxidation-Reduction rxns


Coupled reactions

-Reduction potential--measure of the tendency to lose e-, more negative more likely to lose e-, more + more likely to take e-

-as e- move from donors to acceptors, E is released--syn. ATP, do work


Electron Transport Chain

-Glucose transfers e- to NAD+ to form NADH
-NADH transfers e- to O2

-e- pass though a series of electron carriers in ETC

-each carrier has a slightly less negative red. pot. then previous

-E is released and used to make ATP

-ETC important in cellular E conservation

-prokaryotes--found in plasma membrane and internal membranes

-eukaryotes--found in mitochondrial cristae andchloroplast thylakoid membranes


Electron carriers

NAD+/NADH, FAD/FADH2, Coenzyme Q, Cytochrome: Heme,



-the reduced form (carries electrons) of NAD + (nicotinaminde adenine dinucleotide). this is the most common electron carrier in cellular respiration
-E as excited e- --stores high E e-, favorable e- donor, "reducing equivs"

-makes 3 ATP



-flavin adenine dinucleotide; active carrier produced by citric acid cycle; donates electrons
-E carrying, substrate for ox. phos. in mito.

-coenzyme, e- carrier, transfers e- from Krebs cycle to ETC at a lower E level

-makes 1.5 ATP


Coenzyme Q

- an electron carrier in the electron transport chain
- also known as ubiquinone because it is a ubiquitous quinone

- shuttles protons and electrons across the inner protein complexes of the mitochondrial membrane ETC

-can transfer 1 or 2 e-, mobile within membrane


Cytochrome Heme Proteins

Electron carrier, with iron alternating between Fe2+ and Fe3-


Nutritional Types

-Nutrients provide the basic materials for building biological molecules
-source of E and e- for reducing molecules during biosyn.

-microorgs. are categorized based on their C, E, and e- sources

-nearly all pathogenic mircobes are chemoorganoheterotrophes

-some microbes are able to alter their metabolism in response to environmental conditions


Carbon Source

-Autotrophs--use inorganic C, usually CO2, as sole source of C--Methanotrophs can use CH4
-Heterotrophs--require an organic carbon source (sugar), cannot use CO2


Energy Source

-Phototroph--use light as E source
-Chemotroph--obtain E through the oxidation of organic/inorganic compounds


Electron source

-Lithotroph--uses inorganic substances as e- source (Fe+2-->Fe+3)
-organotroph--uses organic compounds as an e- source



-use CO2 and inorganic chemicals for C, light for E, inorganic e- donor



-fix CO2 as C source, organic chemicals as E source, e- donor from inorganic source
-deep sea vent bacteria



-E from light, sugar for C source, sugars for e-
-purple sulfur bacteria



-sugars for C, E, and e- source



-Use a wide variety of organic molecules as C/E/e- source--proteins, polysaccs, lipids
-Broken down into subunits and converted to glucose or intermediate metabolite

-allows the cell to maintain minimal machinery while being able to utilize many diff nutrients
-sugars for C, E, and e- source
-glycolysis, TCA, oxid. phos. and ETC, O2 as e- acceptor (aerboes)



-Breaks down glucose to pyruvate
-Embden-Meyerhof pahtway

-Pentose-phosphate pahtway

-entner-doudoroff pathway

-reactions occur in cytosol and metabolite intermediates can be shuffled from one pathway to another

-need to be able to summarize: starting points, products, critical/unique enzymes involved, ATP yields, metabolic roles of each pathway



-Most common pathway
-produces several precuroser molecules for biosyn pathways

-divided into 6 C phase and 3 C phase

-requires input of 2 ATP

-each glucose produces--Net 2 ATP by sub. level phos., 2 molecules of pyruvate -->TCA, 2 molecules of NADH --> syn. ATP by oxid. phos.


Pentose Phosphate Pathway

-primary function is to generate NADPH--source of e- for reducing molecules during biosyn.
-provides precursors for biosyn.--aromatic AA and NA

-intermediates can enter EMP

-Starts with G-6-P from EMP or group translocation

-2 key enzymes--transaldolase and transketolase

-products cycle back through pathway until G-6-P completely broken down into CO2

-Net yield from 3 G-6-P: 6 NADPH, 2 fructose-6-P, Glyceraldehyde-3-P--> pyruvate by EMP



-NADH--for ATP
-NADPH--for biosyn.


Entner-Doudoroff Pathway

-Found in some soil bacteria and a few other gram neg.
-one key enzyme is KDPG aldolase--converts 2-keto-3-deoxy-6-phosphoglucanate to pyruvate and glyceraldehyde-3-P

-Glyceraldehye-3-P enters EMP to form pyruvate

-Net yield: 1 ATP, 1 NADH, 1 NADPH per glucose


Tricarboxylic Acid Cycle

-Oxidizes pyruvate to 3 CO2
-also called Kreb's cycle or TCA

-First step uses a multienzyme complex (pyruvate dehydrogenase comples) to convert pyruvate to Acetyl CoA + NADH + CO2

-Acetyl CoA enters the TCA and is borken down to CO2 through a series of redox rxns

-net yield: 4 NADH, 1 FADH2, ! GTP


About the Tricarboxylic Acid Cycle

-Considered a cycle bc one of starting products is regenerated in the process (oxaloacetate)

-CoA (cofactor) is added at 2 points bc it provides a high E thiol linkage that makes next rxn energetically favorable

-some microbes lack complete TCA, but contain most of the components


Electron Transport Chain

-electrons are transferred from NADH and FADH2 to O2 through a series of e- carriers-Eurkary. ETC in inner mito membrane--4 protein complexes connected by cyto. C and CoQ
(in plasma membrane of prokary.)
-for ever e- transfered, 10H+ tranfered out of cell (2 for complex 4)


Iron Sulfur Centers 

* Iron is NOT in a heme group. 
* The iron is linked to inorganic sulfur ions as part of the iron-sulfur center. 
* Centers contain either 2 Fe and 2 S or 4 Fe and 4 S and these are linked to the protein by cysteine residues. 
* Whether it be 2 Fe and 2 s, or 4 Fe and 4 S, the center can only accept or donate one electron


Bacterial ETC

-within plasma membrane or internal membranes
-e- carriers vary

-extensively branched

-e- can enter and exit the chain at several points

-chain may be shorter-->release of less E


BD pathway v. BO pathway

-bacterial ETC
BD: low O2 concentration, 2H+ pumped
BO: greater O2 concentration, 4H+ pumped


Oxidative phosphorylation

-syn. of ATP as the results of e- transport driven by the oxidation of a chemical E source
-e- transport leads to movement of H+ across the membrane--matrix--> intermembrane space, cytoplasm--> periplasmic space (Creates proton motive force, fuels ATP synthase)


Proton Motive Force

-charge/concentration gradient across memrane
-used to do work when protons flow back into the cell--syn. of ATP from ADP and Pi, movement of flagella, transport of molecules across membrane


ATP synthase

-enzyme that uses PMF to syn. ATP
-located in plasma membrane of bacteria--cristae of eukary.

-flow of protons causes conformational changes in ATP synthase that allow binding of ADP and Pi, syn. of ATP, and release of ATP


Maximum ATP yield (chemoorganotrophs, eukary.)

-substrate level phos. produced: 2ATP + 2GTP
-Oxid. phos. produced: 10NADH (1NADH=2.5ATP) + 2FADH2 (1FADH2=1.5 ATO)

-max total yield is 32 ATP

-generally much lower in bacteria, esp. under low oxygen conditions

-PMF used for other activities

-intermediates removed from pathway


Anaerobic Respiration

-Uses a molecule other than O2 as the terminal e- acceptor in the ETC
-generally nitrate, sulfate, or CO2

-Produces less E, bc their reduction potential is less than O2



-Process converting nitrate to N2 gas
-Paracoccus denitrificans, Pseudomonas species, Bacillus species

-will perform aerobic respiration if O2 is available

(faculative anaerobes)


Methanogens (archaea)

-obligate anaerobes
-reduce carbonate or CO2 to methane


Sulfur reducers

-obligate anaerobes
-Desulfovibrio an Desulfurmonas

-reduce sulfate to sulfide



-lack TCA cycle or ETC

-ATP produced by SLP only

-NADH produced by glycolysis reduces pyruvate or its derivative

-acid fermentation or alcohol fermentation--mixed acid fermentation


Catabolism of Carbohydrates

-microbes can utilize many diff carbs
-polysaccs and disaccs are borken down to monosaccs

-monosaccs enter glycolysis directly or are converted to G-6-P or F-6-P

-must have right enzymes in order to convert diff carbs


Catabolism of Lipids

Triacylglycerols are hydrolyzed to glycerol and FA by lipases
-glycerol is converted to dihydroxyacetone phosphate and enters EMP

-FA are oxidized in the B-oxidation pathway to form acetyl-CoA, NADH, and FADH2 (make acetyl-CoA by cutting off 2 C's at a time and adding CoA


Catabolism of Proteins

-Proteins are hydrolyzed to AA that are then deaminated
-the organic acid is then converted to pyruvate, acetyl-CoA or an intermediate of the TCA cycle



-obtain e- for ETCs from the oxidation of inorganic molecules, not from NADH produced by the oxidation of glucose
-need e- for building new molecules too-molecules to donate in ETC have lower reduction potentials than NAD+/NADH, so e- start later in the ETC chain, meaning less E is released and less protons can be pumped

-mostly aerobic, so terminal e- aceptor is O2, but donors can come in lower on the chain


Hydrogen-Oxidizing Bacteria

-Use hydrogen gas as e- donor
-H2/2H+ has a very neg. reduction potential

-can donate electron to ETC or to NAD+

-alcaligenes, pseduomonas, hydrogenobacter


Nitrifying bacteria

-nitrification--oxidize ammonia to nitrate, sewage treatment
-nitrosomas: converts ammonia to nitrate

-Nitrobacter: converts nitrite to nitrate

-unuseable for of N to a useable for for humans


Sulfur-Oxidizing bacteria

-Sulfur-oxidizing bacteria oxidize sulfur, hydrogen sulfide, thiosulfate, etc. to sulfuric acid--ecological impact (intestines--ouch!)
-Beggiatoa, Thiobacillus, Thiomagarita

-acid limits growth of other bacteria, so no competition and can grow freely


reverse electron flow

-both sulfur-oxidizing and nitrifying bacteria use reverse e- flow to generate NADH
-e- can move up or down the ETC depending on cells need for NADH or ATP

-reverse ETC requires E, gives you reducing power so can build molecules

-e- move down the ETC and produce ATP

-when NADH is needed, e- move up the ETC to reduce NAD+ to NADH

-driven by the pmf



-use light E to syn. ATP and reducing power
-use the ATP and reducing power for CO2 fixation

-3 types of photorophy--oxygenic photosyn., anoxygenic photosyn., rhodopsin-based phototrophy (very diff from other two types)


Oxygenic photosyn.

-Oxygen released
-cholorphyll, carotenoids, and phycobiliproteins used to trap light E

-assembled into complex networks called light harvesting antennas

-located in the plasma membrane in bacteria

-located in the cholorplast of eukaryotes

-Two complexes: PSI and PSII, work in tandem

-light E causes release of e- from PSI to e-carriers--cycle back to PSI-->ATP, reduce NADP+-->NADPH



-light E causes the release of e- from PSII--pass through e-carriers to replace e- lost by PSI, generates ATP
-water donates e- to PSII--release of Oxygen

-ATP syn. occurs as a result of pmf

-PSII--e- from water or excited by light, excites PSII, goes to ETC, creates pmf, makes ATP; e- can go to PSI

--PSI-e- from PSII or excited by light, cycles back to PSI to make ATP through ETC, or go to NADP+ to make NADPH, noncyclic


Anoxygenic photosynthesis

-phototrophic green bacteria, phototrophic purple bacteria, heliobacteria
-strict anaerobes-- use a molecule other than water as an e- source, so oxygen is not produced

-bacteriochlorophylls are the light harvesting pigments, carotenoids

-have only one PS, cyclic e- flow--generates pmf for ATP syn, does not produce NAD(P)H

-syn. of NAD(P)H--oxidation of H gas, reverse e- flow, pull e- from ETC at higher E state


Rhodopsin-based phototrophy

-light E cause membrane protein archaeorhodopsin to transport protons across the membrane
-pmf is used to syn. ATP

-does not involve ETC