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.

• How is ATP an intermediate between catabolism and anabolism?

• What is a coenzyme?

• Why is enzyme specificity important?

• What happens to an enzyme below its optimal temperature? Above its optimal temperature?

• Why is glucose such an important molecule for organisms?

• Outline the three ways that ATP is generated.

• What are the principal products of the Krebs cycle?

• How do carrier molecules function in the electron transport chain?

• How does the the energy yield (ATP) of aerobic and anaerobic respiration compare?

• What two compounds that can be made from pyruvic acid by an organism that uses fermentation did we discuss in class? How does this fermentation reaction work?

• On what biochemical basis are Pseudomonas and Escherichia differentiated?

• As far as energy and carbon sources are concerned, most medically important microbes belong to which group?

SLOs cont.: Check Your Understanding

Catabolic and Anabolic Reactions • Metabolism: Definition?

• Catabolism: Provides __________ and _________________ for anabolism.

• Anabolism: Uses __________ and _________________ to build large molecules

Big Picture

Role of ATP in Coupling Reactions A 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 = ___________ __________

Specific; not used up in reaction

Fig 5.3

Enzyme Components

• 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 (DNA-ligase)

• Hydrolases (Sucrase)

• Etc.

Fig 5.4

Factors Influencing Enzyme Activity

Enzymes can be ___________ by temperature and pH

Fig 5.6

Functional protein

Factors Influencing Enzyme Activity: Substrate concentration

Figure

5.5c

Inhibitors

Competitive inhibitors

Noncompetitive – 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: Direct transfer of a high-energy PO

4

– to ADP.

2. Oxidative phosphorylation: transfer of electrons from one compound to another. Final e- acceptor is ___ or other oxidized _________________ _________________ molecules. Chemiosmosis.

Metabolic Pathways of Energy Production: COH Catabolism

• Cellular respiration – Aerobic respiration – Anaerobic respiration

• Fermentation

The three steps of aerobic respiration 1. Glycolysis (oxidation of _____ to ______) 2. Krebs cycle (oxidation of acetyl CoA to ___) 3. Oxidative phosphorylation (e- transport chain)

Foundation Fig 5.11

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 - NOT COVERED!

The Steps of

Glycolysis

Compare to Fig 5.12

Pyruvate Respiration

Acetyl group of acetyl-CoA enters TCA cycle

Krebs cycle generates ATP and reducing power Precursor metabolites

Other names for Krebs cycle?

Preparatory (Transition) step generates Acetyl-CoA from Pyruvate (decarboxylation)

Compare to

Fig 5.13

Krebs Cycle

Electron Transport Chain (System)

• Formed by series of electron carriers 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

Summary of

Aerobic

Respiration in

Prokaryotes

Fig 5.17

Anaerobic Respiration

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

– NO3-

– SO42-

• 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)

In Science, Fermentation means:

• Use of organic molecule as the final electron acceptor

• Does not involve Krebs cycle or ETC

• Energy yield low

• Great diversity of end products: ____________________ (see Table 5.4)

Fig 5.19

Types of Fermentation

Pathway Eukaryote Prokaryote

Glycolysis

Preparatory step

Krebs cycle

ETC

Location of Carbohydrate Catabolism

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: Sucrase, Lactase, etc.

• Lipid catabolism not covered

Protein Amino acids

Extracellular

proteases

Krebs cycle

Deamination, decarboxylation, dehydrogenation,

desulfurylation Organic acid

Protein Catabolism

Decarboxylation

Fig. 5.22

In Lab: Biochemical Tests for Bacterial Identification: Fermentation Tests

Different species produce different enzymes Test detects presence of enzyme

Mannitol Fermentation:

Fig. 5.23

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 not covered, except for protein biosynthesis, which will be covered in Ch 8.

Clinical Case: More than a Sweet Tooth