Ch 5

Microbial Metabolism

Student Learning Outcomes:Differentiate between, anabolism, and catabolism.Identify the components of an enzyme and describe the mechanism of enzymatic action.List the factors that influence enzymatic activity.Explain what is meant by oxidation–reduction.Describe the chemical reactions of glycolysis.Explain the products of the Krebs cycle.Describe the chemiosmotic model for ATP generation.Compare and contrast aerobic and anaerobic respiration.Describe the chemical reactions and some products of fermentation.Categorize the various nutritional patterns among organisms according to energy and carbon source.

Catabolic and Anabolic Reactions

• Metabolism: The sum of all chemical reactions in an organism

• Catabolism: Provides energy and building blocks for anabolism.

• Anabolism: Uses energy and building blocks to build large molecules

Role of ATP in Coupling ReactionsA metabolic pathway is a sequence of enzymatically

catalyzed chemical reactions in a cell.Metabolic pathways are determined by enzymes, which are

encoded by genes.

Fig 5.1

Collision Theory• states that chemical reactions (formation or

breakage of bonds) can occur when atoms, ions, and molecules collide

• Activation energy is needed for most chemical reactions

• Reaction rate depends on frequency of collisions with enough energy to bring about a reaction.

• Reaction rate can be increased by enzymes or by increasing temperature or pressure

Enzymes lower Activation Energy

Compare to Fig 5.2

Enzymes

• Biological catalysts; specific; not used up in that reaction

• Composition of Holoenzyme: Apoenzyme plus cofactor; or apoenzyme plus coenzyme (NAD+, NADP+, FAD)

• Naming of enzymes (see Table 5.1): Oxidoreductases (e.g.: Lactate dehydrogenase and Cytochrome oxidase); ligases, hydrolases etc.

Fig 5.3

Compare to Fig 5.4

Mechanism of Enzymatic Action

Factors Influencing Enzyme Activity

Enzymes can be denatured by temperature and pH

Figure 5.6

These graphs indicate that optimum enzyme activity will occur at:

A. 25 oC and pH 7.0.

B. 25 oC and pH 5.0.

C. 37 oC and pH 7.0.

D. 37 oC and pH 5.0.

E. 45 oC and pH 7.0.

Factors Influencing Enzyme Activity: Substrate concentration

Figure 5.5c

InhibitorsCompetitive

inhibitorsNoncompetitive – allosteric inhibitors

Fig 5.7

vs

Sulfa drugs

Feedback Inhibition

Also known as end-product inhibition

Controls amount of substance produced by a cell

Mechanism is allosteric inhibition

Fig 5.8

Energy Production: Oxidation-Reduction Reactions

• Oxidation = removal of e-

• Reduction = gain of e-

Fig 5.9

Redox reaction = oxidation reaction paired with reduction reaction.

Oxidation-Reduction cont.

In biological systems, the electrons are often associated with hydrogen atoms.

Biological oxidations are often dehydrogenations.

Fig 5.10

The Generation of ATP

Phosphorylation:

1. Substrate level phosphorylation: transfer of a high-energy PO

4– to ADP.

2. Oxidative phosphorylation: transfer of electrons from one compound to another is used to generate ATP by chemiosmosis.

Metabolic Pathways of Energy Production: COH Catabolism

• Cellular respiration– Aerobic respiration– Anaerobic respiration

• Fermentation

The three steps of aerobic respiration1. Glycolysis (oxidation of _____ to ______)2. Krebs cycle (oxidation of acetyl CoA to ___)3. Oxidative phosphorylation (e- transport chain)

Glycolysis

Multi – step breakdown of glucose into pyruvate

Generates • small amount of ATP (how many?)

• small amount of reducing power – (?)

• Alternative pathways: Pentose phosphate and Entner-Doudoroff

The Steps of Glycolysis

Compare to Fig. 5.12

Krebs Cycle

• Other names?• Preparatory (Transition) step generates

acetyl-CoA from pyruvate (decarboxylation)• Acetyl group of acetyl-CoA enters TCA cycle• Generates ATP and reducing power • Generates precursor metabolites

Compare to Fig 5.13

Krebs Cycle

Electron Transport Chain• Formed by series of electron carriers (cytochromes)

located in ___________

• Oxidation/Reduction reactions. Electron carriers (reducing power) from glycolysis and TCA cycle transfer their electrons to the electron transport chain

• Generates proton gradient or proton motive force (pmf)

• In chemiosmosis, pmf generates energy via oxidative phosphorylation

Electron Transport and the Chemiosmotic Generation of ATP

Fig. 5.16 See Textbook Animations

Foundation Figure Fig 5.11

Overview of Respiration and Fermentation

Also review Fig 5.17

Anaerobic Respiration

• Inorganic molecule is final electron acceptor, e.g.:– NO3

- – SO4

2-

• ATP yield lower than in aerobic respiration because only part of Krebs cycle operates under anaerobic conditions.

Fermentation• Any spoilage of food by microorganisms (general use)• Any process that produces alcoholic beverages or acidic dairy

products (general use)• Any large-scale microbial process occurring with or without

air (common definition used in industry)

Scientific definition:• Uses an organic molecule as the final electron acceptor• Does not use the Krebs cycle or ETC• Energy yield low• Diversity of end products: _____________________(see Table 5.4)

The Relationship of Fermentation to Glycolysis

Not in book.However, compare to Fig 5.18

Pathway Eukaryote Prokaryote

Glycolysis

Preparatory step

Krebs cycle

ETC

Location of Carbohydrate Catabolism

Pathway ATP Produced NADH Produced

FADH2 ProducedGlycolysis

Preparatory step

Krebs cycle

Total

Energy produced from complete oxidation of one glucose molecule using aerobic respiration

Pathway By Substrate-Level Phosphorylation

By Oxidative Phosphorylation

From NADH From FADH

Glycolysis

Intermediate step

Krebs cycle

Total

ATP produced from complete oxidation of one glucose using aerobic respiration

Catabolism of Other Compounds

• Polysaccharides and disaccharides–Amylases for digestion of ___________

(very common)–Cellulase for digestion of __________

(only bacteria and fungi have this enzyme)–Disaccharidases

• Lipid catabolism not covered

Protein Amino acids

Extracellular proteases

Krebs cycle

Deamination, decarboxylation, dehydrogenation, desulfurylation

Organic acid

Protein Catabolism

Decarboxylation

Biochemical Tests and Bacterial Identification: Fermentation Tests

Different species produce different enzymes test detects enzyme

Mannitol Fermentation:

Metabolic Diversity among Organisms

• Energy source: Phototrophs vs. Chemotrophs

• Principal carbon source: Autotrophs vs. Heterotrophs

• Chemoheterotrophs use organic compound as energy source and carbon source. Most medically important bacteria.

• Saprophytes vs. parasites

Anabolic Pathways

From Photosyntheis on not covered, except for • Protein biosynthesis (see Ch 8)• Definition of chemoheterotroph