Ch 5 - Microbial metabolism · Microbial metabolism Chapter 5 BIO 220 Metabolism • Sum of all the...

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Microbial metabolism

Chapter 5

BIO 220

Metabolism

• Sum of all the chemical reactions occurring in

an organism

• Metabolism = Catabolism + Anabolism

Fig. 5.1

Collision Theory

• In order for chemical reactions to take place,

atoms/ions/molecules must collide with each

other

• The energy transferred during these collisions

allows for the formation or the break down of

chemical bonds

Enzymes

• Enzymes increase reaction rate by increasing

the probability that substrates will interact in

an orientation necessary for product

formation

• They lower the Energy of Activation of the

reaction (decrease the randomness of

substrate interactions)

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Activation energy

Fig. 5.2

Enzyme action

Fig. 5.3

Enzyme Characteristics

1. Biological catalysts

– Can process substrates very efficiently

– Turnover number

2. Induced fit vs. lock and key

3. Usually proteins

4. Substrate smaller than enzyme

5. Specificity (affinity)

6. Naming

– End in -ase

– Based on type of chemical reactions they catalyze

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Enzyme components

• Some enzymes require additional factors in

order to function

• Holoenzymes are composed of an apoenzyme

(protein) and a cofactor (nonprotein)

Fig. 5.4

Enzyme components

Types of cofactors

• Metal ions

– Zn2+ , Fe2+ , Cu2+ , Mg2+ , Ca2+

• Coenzymes (organic)

– Often derived from vitamins

– Attachment to protein is non-covalent (not

permanent)

Examples of coenzymes

• Nicotinamide adenine dinucleotide (NAD+)

• Nicotinamide adenine dinucleotide

phosphate (NADP+)

• Flavin mononucleotide (FMN)

• Flavin adenine dinucleotide (FAD)

• Coenzyme A

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Factors that affect enzyme activity &

reaction rate

1. Temperature

2. pH

3. Substrate concentration

4. Inhibitors

Temperature

Figs. 5.5a and 5.6

pH

Figs. 5.5b and 5.6

Substrate concentration

Fig. 5.5c

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Inhibitors

• May be competitive or noncompetitive

Fig. 5.7

Competitive inhibition

Inhibitors

• May be competitive or noncompetitive

Fig. 5.7

Feedback inhibition

Fig. 5.8

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Energy production

• Oxidation – reduction

– Used to extract energy from nutrient molecules

• Mechanisms of ATP generation

Oxidation-reduction

• Oxidation and reduction reactions are coupled

(redox reactions)

• Most biological oxidation reactions involve the

loss of hydrogen ions (dehydrogenation rxns)

Figs. 5.9, 5.10

ATP generation

• Nutrient molecules are catabolized using a

series of oxidation-reduction reactions, then

the energy contained within the bonds of the

nutrients can be trapped within the bonds of

ATP, which can then serve as an energy source

for energy-requiring reactions

ATP generation

• Substrate – level phosphorylation

• Oxidative phosphorylation

• Photophosphorylation

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Carbohydrate catabolism

• Glucose is the preferred CHO for energy

production

• Microbes can use either cellular respiration or

fermentation

Fig. 5.11

(Cellular) Respiration

• An ATP-generating process in which molecules

are oxidized and the final electron acceptor

comes from outside the cell and is (almost)

always inorganic

• Aerobes use oxygen as the final electron

acceptor

• Anaerobes do not use oxygen, rather some

other inorganic molecule as the final acceptor

Cellular respiration

• Glycolysis

• Transition reaction

• Krebs cycle

• Electron transport chain (system)

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Glycolysis

Fig. 5.12

Transition reaction and Krebs cycle

Fig. 5.13

Electron transport chain

Carrier molecules include

• Flavoproteins

– Flavin mononucleotide (FMN)

• Cytochromes

• Ubiquinones

Electron transport chain (system)

Fig. 5.14

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Electron transport chain (system)

Fig. 5.16

Chemiosmosis

Fig. 5.15

Fig. 5.17

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Aerobic respiration (summary) Anaerobic respiration

• The final electron acceptor is NOT oxygen

• Pseudomonas and Bacillus use nitrate ions

• Desulfovibrio uses sulfate

• Other organisms use carbonate

• Aerobic respiration is a much more efficient

ATP producer than anaerobic respiration!

Fermentation

• Releases energy from sugars or other organic

molecules

• Does not require oxygen

• Does not use the Krebs cycle or an electron

transport system

• Uses organic molecules as final electron

acceptors

• Does not produce buckets of ATP

Fig. 5.18

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Types of

fermentation

Fig. 5.19

Catabolism of nutrients

Fig. 5.21