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Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint ® Lecture Slides for ROBERT W. BAUMAN MICROBIOLOGY Chapter 5 Microbial Metabolism

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Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint® Lecture Slides for

ROBERT W. BAUMAN

MICROBIOLOGY

Chapter 5

Microbial Metabolism

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• The sum total of chemical reactions that take place within cells (of an organism)

Microbial Metabolism

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• Metabolic processes guided by 8 elementary statements

• Every cell acquires __________

• Metabolism requires energy from light or from catabolism of nutrients

• Energy is stored in __________________________

• Cells catabolize nutrients to form precursor metabolites

• Precursor metabolites, energy from ATP, and enzymes used in anabolic reactions

• Enzymes plus ATP form ______________

• Cells grow by assembling macromolecules

• Cells reproduce once they have doubled in size

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• Catabolism and Anabolism

• Oxidation and ___________ Reactions

• ATP Production and Energy Storage

• The Roles of Enzymes in Metabolism

Basic Chemical Reactions Underlying Metabolism

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Catabolism and Anabolism

• ______________ pathways release energy by breaking down complex molecules to simpler compounds.

• This energy is stored in organic molecules until it needs to do work in the cell.

• _____________ pathways consume energy to build complicated molecules from simpler compounds.

• The energy released by catabolic pathways is used to drive anabolic pathways.

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• Chemical reactions can be classified as either exergonic or endergonic based on free energy.

• An exergonic reaction proceeds with a net release of free energy and delta G is negative.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• Free energy released by a reaction is then available to perform _________.

• For the overall reaction of cellular respiration:

• C6H12O6 + 6O2 -> 6CO2 + 6H2O

• delta G = -686 kcal/mol

• Through this reaction 686 kcal have been made available to do work in the cell.

• The products have 686 kcal less energy than the reactants.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• An endergonic reaction is one that absorbs free energy from its surroundings.

• Endergonic reactions store energy,

• delta G is positive, &

• reactions are nonspontaneous.

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Fig. 6.6b

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• If cellular respiration releases 686 kcal, then photosynthesis, the reverse reaction, must require an equivalent investment of energy.

• Delta G = + 686 kcal / mol.

• Photosynthesis is steeply endergonic, powered by the absorption of light energy.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• Reactions in closed systems eventually reach equilibrium and can do no work.

• A cell that has reached metabolic equilibrium is dead!

• ________________________ is one of the defining features of life.

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Fig. 6.7a

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• Cells maintain disequilibrium because they are open with a constant flow of material in and out of the cell.

• A cell continues to do work ___________________.

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Fig. 6.7b

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Fig. 6.7c

What is a term for a

huge amount of

energy released all

at once?

• A catabolic process in a cell releases free energy in a series of reactions, not in a single step.

• Some reactions of respiration are constantly

• “pulled” in one direction.

• Therefore the product of one reaction does not accumulate, but becomes the reactant in the next step.

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• Sunlight provides a daily source of free energy for the photosynthetic organisms in the environment.

• Nonphotosynthetic organisms depend on a transfer of free energy from photosynthetic organisms in the form of ___________________.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• Transfer of electrons from molecule that donates electron to molecule that accepts electrons

• These reactions are always coupled

• Cells use electron carrier molecules to carry electrons (often in H atoms)

Oxidation and Reduction Reactions

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• Three important electron carriers

• Nicotinamide adenine dinucleotide (NAD+) → NADH

• Nicotinamide adenine dinucleotide phosphate

• (NADP+) → NADPH

• Flavine adenine dinucleotide (FAD) → FADH2

Oxidation and Reduction Reactions

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• Energy released from nutrients can be stored in high-energy phosphate bonds of ATP

• Phosphorylation – organic phosphate is added to substrate

• Anabolic pathways use some energy of ATP by breaking a ______________

ATP Production and Energy Storage

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• Cells phosphorylate ADP to ATP in three ways

• Substrate-level phosphorylation

• ____________ phosphorylation

• Photophosphorylation

• Anabolic pathways use some energy of ATP by breaking a phosphate bond

ATP Production and Energy Storage

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• Enzymes are organic catalysts – increase the likelihood of a reaction

• They are not permanently changed in the reaction

• __________ activation energies

• Speed up reactions

• __________ for a substrate

enzyme

• Substrate Products

The Roles of Enzymes in Metabolism

Substrate-level phosphorylation

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• Six categories of enzymes based on mode of action

• Often named after substrate or action

• Hydrolases – remove hydrogens

• Isomerases – rearrange atoms

• Ligases or polymerases – join molecules (add monomers)

• Lyases - breaking of chemical bonds

• Oxidoreductases

• Transferases – transfer functional groups

The Roles of Enzymes in Metabolism

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• The turnover number is generally 1-________ molecules per second.

Enzymes

Figure 5.4

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The Makeup of Enzymes

• Most enzymes are proteins

• Some are RNA molecules called ribozymes

• Holoenzymes are composed of

• Apoenzymes - protein portions that are inactive if not bound to co-factors

• Cofactors – nonprotein (inorganic ions or coenzymes)

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.5

Enzyme Activity

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.7

Enzyme Activity

Sucrose ------->

fructose + glucose

sucrase

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• Many factors influence the rate of enzymatic reactions

• Temperature

• __________

• Enzyme and substrate concentrations

• Presence of ___________

Enzyme Activity

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.8a

Temperature

What happens to a

protein when the

temperature is to high?

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• Enzymes can be denatured by temperature and pH

Factors Influencing Enzyme Activity

Figure 5.6

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.8b

pH

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.8c

Substrate Concentration

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• Substances that block an enzyme’s active site

• Do not denature enzymes

• Types of Inhibitors

• Competitive inhibitors

• Noncompetitive inhibitors

Inhibitors

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.10

Competitive Inhibitors

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.11a

Noncompetitive Inhibitors

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.12

Feedback Inhibition

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.12

Feedback Inhibition

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• Organisms oxidize carbohydrates as the primary energy source for anabolic reactions

• Glucose used most commonly

• Glucose catabolized by

• Glycolysis

• Cellular respiration → Utilizes (glycolysis), Krebs cycle, and electron transport chain;

• results in complete breakdown of glucose to carbon dioxide and water

• Fermentation → Utilizes glycolysis then converts pyruvic acid into another compound (organic waste products)

Carbohydrate Catabolism

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.14

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• The oxidation of glucose to pyruvic acid, produces ATP and NADH.

Glycolysis

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• Occurs in cytoplasm of most cells

• Divided into three stages involving 10 total steps

• Energy-Investment Stage

• Lysis Stage

• Energy-Conserving Stage

Glycolysis

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Glycolysis

• Glucose + 2 ATP + 2 ADP + 2 PO4

– + 2 NAD+ 2 pyruvic acid + 4 ATP + 2 NADH + 2H+

• Net Products = 2 pyruvic acid + 2ATP + 2NADH +2H +

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.14

Glycolysis

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.14

Glycolysis

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• Yield fewer molecules of ATP than glycolysis

• Reduce coenzymes and yield different metabolites needed in anabolic pathways

• Two pathways

• Pentose phosphate pathway

• Entner-Doudoroff pathway

Alternatives to Glycolysis

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.16

Pentose Phosphate Pathway

•Pentose phosphate pathway –net gain = 2 NADPH, 1 ATP, and five-carbon precursor metabolites

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.16

Pentose Phosphate Pathway

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.17

Entner-Doudoroff Pathway

•Entner-Doudoroff pathway – net gain = 1 ATP, 2 NADPH, and precursor metabolites

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• Pentose phosphate pathway:

• Uses pentoses and NADPH

• Produces 1ATP + 2 NADPH

• Operates with glycolysis

• Entner-Doudoroff pathway:

• Produces 2 NADPH + 1ATP

• Does not involve glycolysis

• Pseudomonas, Rhizobium, Agrobacterium

Alternatives to Glycolysis

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.14

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings

• Pyruvic acid completely oxidized to produce ATP by a series of redox reactions

• Three stages of cellular respiration

• Synthesis of acetyl-CoA (Intermediate step)

• Krebs cycle

• Electron Transport Chain (ETC)

Cellular Respiration

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.18

Synthesis of Acetyl-CoA

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• Results in:

• Two molecules of acetyl-CoA

• Two molecules of _____

• Two molecules of ______

Synthesis of Acetyl-CoA