Microbiology Module 4

Sum total of all chemical reactions of the cell

Energy required to run cellular metabolism is derived from redox reactions

Energy from redox reactions used to make hi energy phosphate bonds (ATP) and to generate ion gradients (PMF)

• Fueling rxns include metabolic pathways and processes that allow a cell to accumulate basic molecules needed for growth including:
• -carbon based precursor metabolites
• -reducing power in the form of NADH and NADPH
• -Energy reserve in form of PMF and/or ATP

Basic pathways generate 12-13 precursor metabolites, reducing power (NADH/NADPH) and cellular energy (ATP. PMF) needed to make all cellular components

Respiring micro-orgs use green pathways (aerobic or anaerobic respiration)

Fermentig microbes use "pink" pathways but also run some rxns from pentose phosphate and TCA (Krebs) cycles

The more negative the redox potential ( E knot prime) the higher the energy the electrons have

Movement of electrons from glc to NAD/NADP generates reducing power

NADH/NADPH needed for biosynthesis, photosynthesis as well as for providing an initial electron donor for respiration

Common pathway used by most organisms in all domains

As glc is oxidized e's are trasferred to NAD, liberating energy that is trapped by making hi energy phosphate bonds

This hi energy P bond is then used to make ATP from ADP (Substrate level Phosphorylation, SLP)

PEP also contains hi energy bond used to make ATP via SLP

Pyruvate from glycolysis is converted to AcetylCoA which enters the cycle

Fermenting microbes only run the TCA rxns needed to make precursor metabolites, not the whole cycle (A-ketoglutarate used to make all AA's)

Respiring microbes run whole cycle, generating GTP, NADH and FADH2

NADH and FADH2 diffuse to respiratory system located on CM

Interconnect with glycolysis (Shares many intermediates and enzymes with glycolysis)

Yields 5C sugars necessary for nucleotide synthesis

Yields NADPH necessary for biosynthesis and photosynthesis

Provided precursors for aromatic AAs and vitamins

• Alternate pathway to glycolysis found in a few microbes
• (Pseudomonas, enterococcus, and some archaea)

Yields ATP, NADH and NADPH

Usually (not always) carried out under anaerobic condidtions

Energy only generated via SLPs, not respiration

H+ tend to accumulate inside cell (use ATP to pump it out of cell). NADH also builds up

Fermenting microbes must find way to regenerate NAD in order to continue to generate ATP

Homolactic fermentation is very common. Produces lactic acid and regenarates NAD

Movement of electrons thru an electron transport chain (ETC). Membrane containing ETC components required to capture and use liberated energy to produce PMF

Electron carriers arranged on the membrane according to reduction potentials so that electrons move spontaneously generating energy that is extracted in small increments. Carriers MUST touch each other

Energy liberated is used to pump H+ out of cell and produce PMF

Aerobic respiration: O2 is final electron acceptor. Anaerobic respiration--cells may use non-O2 final acceptors

Each NAD accepts 2 e's and 1 H+. One H+ is released to cytoplasm. FAD accepts 2 e's and 2 H+

NADH and FADH2 are produced in cytoplasm and diffuse throughout cell, acting as redox cofactors for enzymes and as initial electron donors for respiration

Coenzyme Q (ubiquinone) is common H-carrier. Transfers/accepts 2 e's and 2 H+. Found in CM and can move around CM and lipid bilayer

Heme is covalently attached to membrane bound cytochromes. Fe is at the core and accepts and transfers 1 electron at a time

Fe-S proteins in the CM also transfer 1 electron at a time, but not from heme group (Non heme-iron, NHI)

Electron carriers are positioned next to H carriers on the membrane at some locations

Energy from spontaneous redx reactions used to take up and then pump H+ out of cell as electrons move between these 2 types of carriers

PMF is generated and then is used to perform cellular tasks (Make ATP for metabolism and photosynthesis, run flagella, active transport, etc)

ATP synthase (F1F0 ATPase)

F0 is proton pump--it turns as H+ flow INTO the cell thru the channel and interact with charged residues

The Gamma (Y) subunit of F1 interacts w/F0 and also turns, synthesizing ATP

Also works in reverse by fermenters to pump excess H+ out of cell ( using ATP as energy source)

Variety of final electron acceptors can be used in place of O2

Include: S, Fe3+, CO2, and NO3

Greatly extends possible microbial habitat

Under aerobic conditions e's feed into respiration from NADH or CH3OH and O2 is final electron acceptor

Under Anaerobic conditions diff. respiratory cmpnts are made and inserted into CM and several diff. final acceptors give rise to NO2-, N2O and N2

Use a variety of Inorganic initial electron donors for respiration. Typically in nutrient deficient environments

Usually respiration is aerobic, but may be anaerobic

Reverse respiration can be used to generate NAD(P)H

Special molecules (Chlorophyl) absorb light energy and use it to elevate reduction potentials of e's. E's then flow thru an ETC to generate PMF, ATP

Some microbes contain bacteriorhodopsins (light-driven H+ pumps that directly generate PMFs w/out respiratory chains)

Chlorophylls (oxygenic photosynthesis) and BChls (non-oxygenic) are inserted in CM with long hydrophobic tails

Many diff types of Chls/BChls, each absorbing diff. wavelengths of light. All use Mg

Accessory pigments surround (B)Chls. Also absorb and transfer energy (@ diff. WV) within complexes called reaction centers

Initial electron donor and final are same (BChl) but electron can be funneled in and out

Reduction potentials allow flow of electrons to produce PMF

NAD+ can be reduced and exit the system

Reverse electron flow in purple bacteria can generate NADH/NADPH

Systems are anoxygenic and always uses BChls.

2 photosystems are used. Chls are used (oxygenic)

O2 is produced (1st step) when H2O is used as initial electron donor

Light is absorbed and transferred to electrons in 2 phases and a PMF is generated

NADP+ is final electron acceptor, producing NADPH for use in production of carbohydrate

Members of rhodopsin superfamily--ALL use light absorbed by retinal

Light-induced conformational changes in bacteriorhodopsins cause H+ to be pumped out of cells

Some bacteriorhodopsins act as photoreceptors (absorb light and then cause PMF)

During aerobic metabolism reactive oxygen intermediates are formed, including O2 and H2O2

SOD (superoxide dismutase) converts very toxic superoxide anion into O2 and H2O2 and Catalase/peroxidase converts H2O2 into O2 and H2O

Microbes contain levels of these enzymes that are proportional to levels of O2 in environment

• Obligate Aerobe: +SOD and +Catalase
• Facultative Anaerobe: +SOD and +Catalase
• Aerotolerant Anaerobe: +SOD and -Catalase
• Strict Anaerobe: -SOD and -Catalase but +peroxidase
• Microaerophile: +SOD and +Catalase (Low levels)