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Chapter 5
Microbial Metabolism
Catabolic and Anabolic Reactions
5-1 Define metabolism, and describe the fundamental differences
between anabolism and catabolism.
5-2 Identify the role of ATP as an intermediate between catabolism and
anabolism.
Catabolic and Anabolic Reactions
Metabolism: the sum of the chemical reactions in
an organism
Catabolic and Anabolic Reactions
Catabolism: provides energy and building blocks for anabolism
Anabolism: uses energy and building blocks to build large molecules
Catabolic and Anabolic Reactions
A metabolic pathway is a sequence of enzymatically catalyzed chemical
reactions in a cell
Metabolic pathways are determined by enzymes
Enzymes are encoded by genes
Check Your Understanding
Distinguish catabolism from anabolism. 5-1
How is ATP an intermediate between catabolism and anabolism? 5-2
Enzyme
5-3 Identify the components of an enzyme.
5-4 Describe the mechanism of enzymatic action.
5-5 List the factors that influence enzymatic activity.
5-6 Distinguish competitive and noncompetitive inhibition.
5-7 Define ribozyme.
Collision Theory
The collision theory states that chemical reactions can occur when atoms,
ions, and molecules collide
Activation energy is needed to disrupt electronic configurations
Reaction rate is the frequency of collisions with enough energy to bring
about a reaction
Reaction rate can be increased by enzymes or by increasing temperature
or pressure
Enzyme Components
Biological catalysts
Biological catalysts
Specific for a chemical reaction; not used up in that reaction
Apoenzyme: protein
Cofactor: nonprotein component
Coenzyme: organic cofactor
Holoenzyme: apoenzyme plus cofactor
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Important Coenzymes
NAD+
NADP+
FAD
Coenzyme A
Enzyme Specificity and Efficiency
The turnover number is generally 1 to 10,000 molecules per second
Enzyme Classification
Oxidoreductase: oxidation-reduction reactions
Transferase: transfer functional groups
Hydrolase: hydrolysis
Lyase: removal of atoms without hydrolysis
Isomerase: rearrangement of atoms
Ligase: joining of molecules; uses ATP
Factors Influencing Enzyme Activity
Temperature
pH
Substrate concentration
Inhibitors
Factors Influencing Enzyme Activity
Temperature and pH denature proteins
Enzyme Inhibitors:
Competitive Inhibition
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Enzyme Inhibitors:
Noncompetitive Inhibition
Enzyme Inhibitors: Feedback Inhibition
Ribozymes
RNA that cuts and splices RNA
Check Your Understanding
What is a coenzyme? 5-3
Why is enzyme specificity important? 5-4
What happens to an enzyme below its optimal temperature? Above its
optimal temperature? 5-5
Why is feedback inhibition noncompetitive inhibition? 5-6
What is a ribozyme? 5-7
Energy Production
5-8 Explain the term oxidation-reduction.
5-9 List and provide examples of three types of phosphorylation
reactions that generate ATP.
5-10Explain the overall function of metabolic pathways.
Oxidation-Reduction Reactions
Oxidation: removal of electrons
Reduction: gain of electrons
Redox reaction: an oxidation reaction paired with
a reduction reaction
Oxidation-Reduction Reactions
In biological systems, the electrons are often associated with hydrogen
atoms
Biological oxidations are often dehydrogenations
The Generation of ATP
ATP is generated by the phosphorylation of ADP
Substrate-Level Phosphorylation
Energy from the transfer of a high-energy PO4– to ADP generates ATP
Oxidative Phosphorylation
Energy released from transfer of electrons (oxidation) of one compound to
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Oxidative Phosphorylation
Energy released from transfer of electrons (oxidation) of one compound to
another (reduction) is used to generate ATP in the electron transport chain
Photophosphorylation
Light causes chlorophyll to give up electrons
Energy released from transfer of electrons (oxidation) of chlorophyll
through a system of
carrier molecules is used to generate ATP
Check Your Understanding
Why is glucose such an important molecule for organisms? 5-8
Outline the three ways that ATP is generated. 5-9
What is the purpose of metabolic pathways? 5-10
Carbohydrate Catabolism
5-11Describe the chemical reactions of glycolysis.
5-12Identify the functions of the pentose phosphate and EntnerDoudoroff pathways.
5-13Explain the products of the Krebs cycle.
5-14Describe the chemiosmotic model for ATP generation.
5-15Compare and contrast aerobic and anaerobic respiration.
5-16 Describe the chemical reactions of, and list some products of,
fermentation.
Carbohydrate Catabolism
The breakdown of carbohydrates to release energy
Glycolysis
Krebs cycle
Electron transport chain
Glycolysis
The oxidation of glucose to pyruvic acid produces ATP and NADH
Preparatory Stage of Glycolysis
2 ATP are used
Glucose is split to form 2 glucose-3-phosphate
Energy-Conserving Stage of Glycolysis
2 glucose-3-phosphate are oxidized to 2 pyruvic acid
4 ATP are produced
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2 glucose-3-phosphate are oxidized to 2 pyruvic acid
4 ATP are produced
2 NADH are produced
Glycolysis
Glucose + 2 ATP + 2 ADP + 2 PO4– + 2 NAD+ → 2 pyruvic acid + 4 ATP +
2 NADH + 2H+
Alternatives to Glycolysis
Pentose phosphate pathway
Uses pentoses and NADPH
Operates with glycolysis
Entner-Doudoroff pathway
Produces NADPH and ATP
Does not involve glycolysis
Pseudomonas, Rhizobium, Agrobacterium
Cellular Respiration
Oxidation of molecules liberates electrons for an electron transport chain
ATP is generated by oxidative phosphorylation
Intermediate Step
Pyruvic acid (from glycolysis) is oxidized and decarboxylated
The Krebs Cycle
Oxidation of acetyl CoA produces NADH and FADH2
The Electron Transport Chain
A series of carrier molecules that are, in turn, oxidized and reduced as
electrons are passed down the chain
Energy released can be used to produce ATP by chemiosmosis
A Summary of Respiration
Aerobic respiration: the final electron acceptor in the electron transport
chain is molecular oxygen (O2)
Anaerobic respiration: the final electron acceptor in the electron transport
chain is NOT O2
Yields less energy than aerobic respiration because only part of the
Krebs cycle operates under anaerobic conditions
Respiration
Anaerobic Respiration
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Respiration
Anaerobic Respiration
Carbohydrate Catabolism
Carbohydrate Catabolism
Energy produced from complete oxidation of one glucose using aerobic
respiration
Carbohydrate Catabolism
ATP produced from complete oxidation of one glucose using aerobic
respiration
Carbohydrate Catabolism
36 ATPs are produced in eukaryotes
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)
Fermentation
Scientific definition:
Releases energy from oxidation of organic molecules
Does not require oxygen
Does not use the Krebs cycle or ETC
Uses an organic molecule as the final electron acceptor
Fermentation
Alcohol fermentation: produces ethanol + CO2
Lactic acid fermentation: produces lactic acid
Homolactic fermentation: produces lactic acid only
Heterolactic fermentation: produces lactic acid and other compounds
Check Your Understanding
What happens during the preparatory and energy-conserving stages of
glycolysis? 5-11
What is the value of the pentose phosphate and Entner-Doudoroff
pathways if they produce only one ATP molecule? 5-12
What are the principal products of the Krebs cycle? 5-13
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What is the value of the pentose phosphate and Entner-Doudoroff
pathways if they produce only one ATP molecule? 5-12
What are the principal products of the Krebs cycle? 5-13
How do carrier molecules function in the electron transport chain? 5-14
Compare the energy yield (ATP) of aerobic and anaerobic respiration. 5-15
List four compounds that can be made from pyruvic acid by an organism
that uses fermentation. 5-16
Lipid and Protein Catabolism
5-17Describe how lipids and proteins undergo catabolism.
5-18Provide two examples of the use of biochemical tests to identify
bacteria in the laboratory.
Protein Catabolism
Protein Catabolism
Biochemical Tests
Used to identify bacteria
Check Your Understanding
What are the end-products of lipid and protein catabolism? 5-17
On what biochemical basis are Pseudomonas and Escherichia
differentiated? 5-18
Photosynthesis
5-19Compare and contrast cyclic and noncyclic photophosphorylation.
5-20Compare and contrast the light-dependent and light-independent
reactions of photosynthesis.
5-21Compare and contrast oxidative phosphorylation and
photophosphorylation.
Photosynthesis
Photo: conversion of light energy into chemical energy (ATP)
Light-dependent (light) reactions
Synthesis:
Carbon fixation: fixing carbon into organic molecules
Light-independent (dark) reaction: Calvin-Benson cycle
Photosynthesis
Light-independent (dark) reaction: Calvin-Benson cycle
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Photosynthesis
Oxygenic:
Anoxygenic:
Cyclic Photophosphorylation
Noncyclic Photophosphorylation
Calvin-Benson Cycle
Check Your Understanding
How is photosynthesis important to catabolism?
5-19
What is made during the light-dependent reactions? 5-20
How are oxidative phosphorylation and photophosphorylation similar?
5-21
A Summary of Energy Production
5-22Write a sentence to summarize energy production in cells.
Check Your Understanding
Summarize how oxidation enables organisms to get energy from glucose,
sulfur, or sunlight. 5-22
Metabolic Diversity among Organisms
5-23Categorize the various nutritional patterns
among organisms according to carbon source and mechanisms of
carbohydrate catabolism
and ATP generation.
Chemotrophs
Use energy from chemicals
Chemoheterotroph
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Energy is used in anabolism
Chemotrophs
Use energy from chemicals
Chemoautotroph, Thiobacillus ferrooxidans
Energy is used in the Calvin-Benson cycle to fix CO2
Phototrophs
Use light energy
Photoautotrophs use energy in the Calvin-Benson cycle to fix CO2
Photoheterotrophs use energy
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Metabolic Diversity among Organisms
Check Your Understanding
Almost all medically important microbes belong to which of the four
aforementioned groups? 5-23
Metabolic Pathways of Energy Use
5-24Describe the major types of anabolism and their relationship to
catabolism.
Check Your Understanding
Where do amino acids required for protein synthesis come from? 5-24
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Check Your Understanding
Where do amino acids required for protein synthesis come from? 5-24
The Integration of Metabolism
5-25Define amphibolic pathways.
The Integration of Metabolism
Amphibolic pathways: metabolic pathways that have both catabolic and
anabolic functions
Check Your Understanding
Summarize the integration of metabolic pathways using peptidoglycan
synthesis as an example. 5-25