5-a Microbial Metabolism pp. 115-138; 144-148

Chapter 5 Overview Metabolism Enzymes Common energy pathways used by microbes Fermentation Aerobic respiration Anaerobic respiration Metabolic diversity among organisms

Metabolism Energy-Balancing Process Release energy Requires energy Catabolism Breakdown of molecules Sugar  CO2 + H20 Provides ‘building blocks’ for anabolism Provides energy for anabolism ATP  ADP + energy Requires energy Anabolism Synthesis of molecules Amino acids  protein Provides molecules for catabolism Provides ATP for catabolism ADP + energy  ATP Molecule breakdown coupled with molecules synthesized

Enzymes …Enable Energy-Balancing Process Are a catalyst = speed up reaction Increase the reaction rate Lower the energy of activation Are not altered in the reaction Are highly specific Each acts on a specific substance, the substrate Each catalyzes only one reaction

Enzymes AB  A + B Provide a structure, a framework To allow collisions to occur And the chemical reaction to occur AB  A + B Substrate Products

Energy Requirements - Chemical Reaction The reaction is: AB  A + B Fig. 5.2

Mechanism of Enzymatic Action: Fig. 5.4a When an enzyme and substrate combine: The substrate is transformed, to products And the enzyme is recovered, unaltered Turnover number ~ 1-10,000 molecules per second

Naming enzymes: Enzyme classification: Names usually end in –ase Based on the type of chemical reaction they catalyze Example: oxidoreductases (ox-redox rxns) Within each class, named for the specific reaction If remove hydrogen, called dehydrogenases

Enzyme classification (6 classes):

Enzyme Components Some enzymes consist only of protein Most consist of both a protein and a non-protein component The protein called an apoenzyme The non-protein part called a cofactor Cofactors are Ions of iron, zinc, magnesium, calcium etc* If a cofactor is an organic molecule, it is called a: Coenzyme * p. 119

Apoenzymes are inactive by themselves Apoenzymes + cofactors form a They must be activated by cofactors Apoenzymes + cofactors form a Holoenzyme + Fig. 5.3

Enzyme & Cofactors NAD+ NADP+ FMN, FAD Coenzyme A Nicotinamide adenine dinucleotide Nicotinamide adenine dinucleotide phosphate Flavin mononucleotide, Flavin adenine dinucleotide Important in the Krebs cycle

Enzymes are characterized by specificity Fig. 5.4b Enzymes are characterized by specificity Specificity is a function of their active sites (see ‘groove’) Enzyme + substrate = slight shape change * Animation: Enzyme–Substrate Interactions. The Microbiology Place.

Organisms - Metabolic Diversity Chemotrophs Oxidation-reduction reactions of organic or inorganic compounds for energy Phototrophs Use light as primary source of energy Autotrophs Use CO2 for principal carbon source Heterotrophs Use organic carbon source

Combine Energy & Carbon Photoautotrophs Energy = light; carbon = CO2 Photoheterotrophs Energy = light; carbon = organic source Chemoautotrophs Energy = organic or inorganic compounds; carbon = CO2 Chemoheterotrophs* Energy = organic or inorganic compounds; carbon = organic source

Nutritional Classification of Organisms Fig. 5.27

Q’s All of the following are enzymes except: Threonine deamainase Acetyl Peroxidase Urease Enzymes work most effectively at their optimal temperature and pH. True b. False

Q’s Beggiatoa bacteria use carbon dioxide for their carbon source and hydrogen sulfide as an energy source. This organism is a: Photoheterotroph Chemoheterotroph Photoautotroph Chemoautotroph Hint: Fig. 5.27

Q’s In the figure shown, what is the small organic molecule called that is needed to activate the apoenzyme? A. Holoenzyme B. Enzyme C. Coenzyme D. Substrate E. Reactant

Q’s A dehydrogenase is an example of a/an _____________? Nitrobacter bacteria use CO2 for their carbon source and nitrate ions as an energy source. This organism is a: Chemoautotroph Chemoheterotroph Photoheterotroph Photoautotroph Hint: Fig. 5.27

Q’s A coenzyme assists an enzyme by accepting or donating matter. What does NAD+ transfer? CoA Electrons Acetyl groups ATP Hint: Table 5.2

Q’s Organisms that use carbon dioxide as a carbon source and energy sources such as ammonia or hydrogen sulfide are called: Photoautotrophs Photoheterotrophs Chemoheterotrophs Chemoautotrophs Hint: Fig. 5.27

Q’s Organism Carbon Source Energy Source Photoautotroph Fill in the blanks: Organism Carbon Source Energy Source Photoautotroph Photoheterotroph Chemoautotroph Chemoheterotroph