Energetics and Catabolism - Weber State Universityfaculty.weber.edu/coberg/2054 slides/Energetics_and_Catabolism.pdf · Energetics and Catabolism ... " Breaking down molecules for

Energetics and Catabolism

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 1


Building the Environment

n Sun is ultimate energy source n Photosynthesis

¨ Captures light, stores as chemical energy n Heterotrophy

¨ Uses captured chemical energy ¨ Builds other chemicals

n Waste ¨ Each step gives off heat energy


Building the Cell

n Catabolism

¨ Breaking down molecules for energy n Anabolism

¨ Using energy to build cell components ¨ Reducing entropy, creating order

n Metabolism ¨ Balance between catabolism and anabolism ¨ Central biochemical pathways used for both

n  TCA cycle, glycolysis, pentose phosphate shunt


Building the Cell

n Predominant energy source is electricity ¨ Electrons passed from A to B

n  A is oxidized, B is reduced n  Energy of electron flow powers the cell

n Photosynthesis ¨ Light reduces electron donors

n Heterotrophy ¨ Reduced compounds used for energy

n Energy used to build cell components


Electron Transfer

n Major source of cell energy ¨ Passage of electrons releases energy

n  Requires electron donor, electron acceptor

n Electron transport found in all cells ¨ Different donors, acceptors

n Electron energy can be stored ¨ Reduced chemicals ¨ Concentration gradient ¨ Phosphorylation of chemicals


Phosphorylation Energy

n  Less energy than oxido-reduction ¨ Useful energy level for most cell reactions

n No electron donor or acceptor needed n Phosphate added via dehydration

¨ Released via hydrolysis n  Water is plentiful

n ATP most common ¨ GTP sometimes

is present

ADP

ATP


Metabolism

Sunlight Reduced geological compounds (rocks, inorganic compounds)

(Reduced) biological macromolecules (starch, fats)

(First energy source)

(Major energy source today) (Energy source

for animals)

Energy

CATABOLISM

Phototrophy Lithotrophy Organotrophy

ATP

Short-term energy storage

ANABOLISM

Carbon, nitrogen, water

Long-term energy storage

Biosynthesis


Enzymes Catalyze Reactions

n Reactions don’t always occur

¨ Even if ΔG < 0 ¨ Kinetic barrier

n  Activation energy

n Enzymes = catalysts ¨ Lower activation energy

n  Remove kinetic barrier ¨ Allow reaction to occur rapidly


Catabolism: The Microbial Buffet

n Microbes have great catabolic diversity ¨ Electron donors

n  Lithotrophy: inorganic molecules n  Organotrophy: organic molecules n  Phototrophy: use light energy to reduce

compounds, then use these as electron donor ¨ Electron acceptors

n  Respiration: inorganic molecules n  Fermentation: organic molecules


Organotrophy

n Wide range of organic compounds digested ¨ Polysaccharides

n  Converted to glucose

¨ Lipids n  Converted to acetyl-CoA

¨ And glycerol

¨ Amino acids ¨ Aromatic compounds

n  Converted to acetyl-CoA


Glucose Breakdown

n Glycolysis ¨ Embden-Meyerhof-Parnas pathway ¨ Glucose is activated

n  Phosphorylated twice by ATP ¨ Activated phospho-sugar is split

n  Converted to glyceraldehyde 3-phosphate

¨ Glyceraldehyde-3-P is oxidized n  Energy stored as ATP n  End product is 2 pyruvates

¨ Requires 2 ATP, yields 4 ATP n  + 2 NADH


Glucose Breakdown

n Entner-Doudoroff Pathway ¨ Used by E. coli ¨ Glucose or sugar acid is activated

n  Phosphorylated once by ATP ¨ Glucose-6-P is oxidized, then split

n  Converted to 6-P-gluconolactone ¨ Then to pyruvate and glyceraldehyde-3-P

¨ Glyceraldehyde-3-P is oxidized n  as in EMP pathway

¨ Requires 1 ATP, yields 2 ATP n  + 1 NADH, 1 NADPH


n Pentose phosphate shunt ¨ Glucose is activated

n  Phosphorylated once by ATP

¨ Glucose-6-P is oxidized twice n  Converted to 6-P-gluconolactone n  Oxidized to to ribulose-5-P

¨ Ribulose-5-P is used for biosynthesis n  Produces ribose for nucleic acids

¨ Requires 1 ATP, yields 2 ATP n  + 2 NADPH

Glucose Breakdown


The Tricarboxylic Acid Cycle

n Respiration ¨ Need to eliminate pyruvate ¨ Oxidize completely to CO2

n  Only possible with inorganic electron acceptor n  Respiration produces more energy than fermentation n  Fermentation only when no inorganic acceptor present

n Pyruvate dehydrogenase complex ¨ Converts pyruvate to acetyl-CoA

n  CO2 diffuses easily out of cell n  Electrons passed to NADH


The TCA Cycle

n Eliminates Pyruvate/AcetylCoA ¨ Oxidize completely to CO2

n  Pyruvate = glycolysis product n  AcCoA = lipid oxidation product

¨ Make ATP n Need oxaloacetate

¨ Add 2C to 4C → 6C ¨ Oxidize twice

n  Eliminate 2C, make ATP

¨ Produce 4C compound n  Succinate


Succinate

Advantage of Cycles

n  Pathway requires source ¨ Oxaloacetate must be supplied

n  Pathway builds up products ¨ Succinate is produced

n  Convert product to source ¨ Solves both problems

n  Always have source reagent

n  Never build up product excess

n  Many cycles in biology


The TCA Cycle

n Coenzyme A carries away CO2 ¨ While oxidizing the molecule ¨ Used 3 times for oxidation of pyruvate

n TCA intermediates used thoughout cell ¨ Form amino acids

n  Oxaloacetate, α-ketoglutarate ¨ TCA used for catabolism and anabolism

n Variant cycles used in some microbes ¨ Glyoxylate cycle


Fermentation

n Glucose is oxidized ¨ NADH is reduced

n  Must be reoxidized to NAD+ + H+

¨ Pyruvate product builds up n  Must be eliminated

n Fermentation ¨ Pass electrons back to pyruvate

n  Or to Acetyl-CoA produced from pyruvate

¨ Convert pyruvate into other products n  Useful for cell, or easy to eliminate

2


Fermentation

n S. cerevisiae (baker’s yeast) ¨ Decarboxylate pyruvate

n  CO2 produced causes bread to rise

¨ Reduce acetaldehyde to ethanol n Vertebrate muscles

¨ Lactate buildup, reoxidized when O2 present n E. coli

¨ Mixed fermentation produces formate, acetate n Propionibacterium

¨ CO2 produced makes holes in cheese


Aromatic Catabolism

n Bacteria can degrade many compounds

¨ Pseudomonas, Rhodococcus n Aromatic compounds converted to pyruvate

¨ Allows growth in wide range of environments ¨ Used for bioremediation

n  Cleaning up oil spills n  Cleaning industrial sites n  Degrading toxic compounds


Gibbs Free Energy

n ΔG = ΔH - TΔS ¨ ΔH = change in enthalpy

n  Release of heat

¨ ΔS = change of entropy n ΔG must be negative for reaction to occur

¨ Reaction can be blocked even if ΔG < 0 n ΔG depends on reactant concentration

¨  n  Low product concentration can drive reaction

[A][B][C][D]RTGG ln+°Δ=Δ


Biochemical Reaction Energy

n ΔG = ΔH - TΔS n Entropy stronger at higher temperatures

¨ Breakdown of a large molecule into small ones ¨ Release of gas

n Diffusion spreads molecules out ¨ Requires energy to

contain them n Gradient = stored energy

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Energetics and Catabolism - Weber State Universityfaculty.weber.edu/coberg/2054 slides/Energetics_and_Catabolism.pdf · Energetics and Catabolism ... " Breaking down molecules for