Chapter 5

Microbial Metabolism

Metabolism - all of the chemical reactions within a living organism1. Catabolism ( Catabolic )

breakdown of complex organic molecules into simpler compounds

releases ENERGY2. Anabolism ( Anabolic )

the building of complex organic molecules from simpler ones

requires ENERGY

Enzymes - catalysts that speed up and direct chemical reactionsA. Enzymes are substrate specific

Lipases LipidsSucrases SucroseUreases UreaProteases ProteinsDNases DNA

Enzyme Specificity can be explained by the Lock and Key Theory

E + S -----> ES ------> E + P

Naming of Enzymes - most are named by adding “ase” to the substrateSucrose SucraseLipids LipaseDNA DNaseProteins Proteaseremoves a Hydrogen Dehydrogenaseremoves a phosphate phosphotase

Naming of EnzymesGrouped based on type of reaction they

catalyze1. Oxidoreductases oxidation &

reduction2. Hydrolases hydrolysis3. Ligases synthesis

Enzyme Components

2 Parts

1. Apoenzyme - protein portion

2. Coenzyme (cofactor) - non-protein

Holoenzyme - whole enzyme

Coenzymes Many are derived from vitamins

1. NiacinNAD (Nicotinamide adenine dinucleotide)

2. RiboflavinFAD (Flavin adenine dinucleotide)

3. Pantothenic AcidCoEnzyme A

Factors that Influence Enzymatic Activity

Denaturation of an Active Protein

Inhibitors can effect enzymatic activity

1. Competitive Inhibitors

2. Noncompetitive Inhibitors

Competitive Inhibitors -compete for the active site

1. Penicillin competes for the active site on the enzyme

involved in the synthesis of the pentaglycine crossbridge

2. Sulfanilamide (Sulfa Drugs)competes for the active site on the enzyme

that converts PABA into Folic AcidFolic Acid - required for the synthesis of DNA and RNA

Selective Toxicity

Non-competitive Inhibitors - attach to an allosteric site

Energy Production1. Oxidation

refers to the loss of Hydrogens and or electrons

2. Reductionthe gain of Hydrogens and or electrons

NAD Cycle

Carbohydrate CatabolismMicroorganisms oxidize carbohydrates as

their primary source of energyGlucose - most common energy sourceEnergy obtained from Glucose by:

RespirationFermentation

Aerobic Cellular Respiration

Electrons released by oxidation are passed down an Electron Transport System with oxygen being the Final Electron Acceptor

General Equation:

Glucose + oxygen----> Carbon dioxide + water

ATP

Chemical EquationC6H12O6 + 6 O2 -------> 6 CO2 + 6 H2O 38 ADP + 38 P 38 ATP

Aerobic Cellular Respiration4 subpathways

1. Glycolysis2. Transition Reaction3. Kreb’s Cycle4. Electron Transport System

1. Glycolysis (splitting of sugar)Oxidation of Glucose into 2 molecules of

Pyruvic acidEmbden-Meyerhof Pathway

End Products of Glycolysis:2 Pyruvic acid2 NADH22 ATP

2. Transition ReactionConnects Glycolysis to Krebs Cycle

End Products:2 Acetyl CoEnzyme A2 CO2

2 NADH2

3. Krebs Cycle (Citric Acid Cycle)Series of chemical reactions that begin and

end with citric acid

Products:2 ATP6 NADH2

2 FADH2

4 CO2

4. Electron Transport SystemOccurs within the cell membrane of

Bacteria

Chemiosomotic Model of Mitchell34 ATP

How 34 ATP from E.T.S. ?3 ATP for each NADH2

2 ATP for each FADH2

NADH2

Glycolysis 2T. R. 2Krebs Cycle 6

Total 10

10 x 3 = 30 ATP

FADH2

Glycolysis 0T.R. 0Krebs Cycle 2

Total 2

2 x 2 = 4 ATP

Total ATP production for the complete oxidation of 1 molecule of glucose in Aerobic Respiration

ATPGlycolysis 2Transition Reaction 0Krebs Cycle 2E.T.S. 34

Total 38 ATP

Anaerobic Respiration Electrons released by oxidation are passed

down an E.T.S., but oxygen is not the final electron acceptor

Nitrate (NO3-) ----> Nitrite (NO2-)Sulfate (SO2

4-) ----> Hydrogen Sulfide (H2S)

Carbonate (CO24-) -----> Methane (CH4)

FermentationAnaerobic process that does not use the

E.T.S. Usually involves the incomplete oxidation of a carbohydrate which then becomes the final electron acceptor.

Glycolysis - plus an additional step

Fermentation may result in numerous end products

1. Type of organism

2. Original substrate

3. Enzymes that are present and active

1. Lactic Acid FermenationOnly 2 ATPEnd Product - Lactic AcidFood SpoilageFood Production

Yogurt - MilkPickles - CucumbersSauerkraut - Cabbage

2 Genera:StreptococcusLactobacillus

2. Alcohol FermentationOnly 2 ATPEnd products:

alcoholCO2

Alcoholic BeveragesBread dough to rise

Saccharomyces cerevisiae (Yeast)

3. Mixed - Acid FermentationOnly 2 ATPEnd products - “FALSE”

Escherichia coli and other enterics

Propionic Acid Fermentation

Only 2 ATPEnd Products:

Propionic acidCO2

Propionibacterium sp.

Fermentation End Products

Lipid Catabolism

Protein Catabolism

Photosynthesis - conversion of light energy from the sun into chemical energy

Chemical energy is used to reduce CO2 to sugar (CH2O)

Carbon Fixation - recycling of carbon in the environment (Life as we known is dependant on this)

PhotosynthesisGreen Plants AlgaeCyanobacteria

Chemical Equation

6 CO2 + 6 H2O + sunlight -----> C6H12O6 + 6 O2

2 Parts:1. Light Reaction2. Dark Reaction

Light ReactionNon-Cyclic Photophosphorylation

O2

ATPNADPH2

Light Reaction (simplified)

2. Dark Reaction