Ch 5
Microbial
Metabolism
Objectives:
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 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 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
Enzymes lower
Activation Energy
Compare
to Fig 5.2
Fig 5.3
Enzymes
• Biological catalysts; specific; not used up in that
reaction
• Enzyme components:
– Apoenzymes, Cofactors, Holoenzymes
– Coenzymes (NAD+, NADP+, FAD)
• Naming of enzymes (see Table 5.1): Lactate
dehydrogenase; Cytochrome oxidase; ligase,
transferase etc.
Mechanism of Enzymatic
Reactions
Compare to
Fig 5.4
Factors Influencing Enzyme Activity
Enzymes can be denatured by temperature and pH
Fig 5.5c
Fig 5.6
Substrate concentration
influencing enzyme activity
Inhibitors
Noncompetitive –
Competitive
vs
allosteric inhibitors
inhibitors
Fig 5.7
Sulfa drugs
Feedback Inhibition
Also known as endproduct 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
-
Redox reaction =
oxidation reaction paired
with reduction reaction.
Fig 5.9
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 Phosphorylation:
ATP
1. Substrate level
phosphorylation:
transfer of a highenergy PO4– 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 respiration
1. 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
• Other names?
Krebs Cycle
• Transition step generates
acetyl-CoA from pyruvate (decarboxylation)
• Acetyl group of acetylCoA enters TCA cycle
• Generates ATP and reducing power
• Generates precursor metabolites
Krebs Cycle
Compare to
Fig 5.13
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
Overview of Respiration and Fermentation
Foundation
Figure
Fig 5.11
Fig 5.17
Anaerobic Respiration
• Inorganic molecule is final electron acceptor,
e.g.:
-
– NO3
–
2SO4
• 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
(see Table 5.4)
• Diversity of end products: _____________________
The Relationship of
Fermentation to
Glycolysis
Not in book
Also view Fig 5.18
Location of Carbohydrate Catabolism
Pathway
Glycolysis
Intermediate step
Krebs cycle
ETC
Eukaryote
Prokaryote
Energy produced from complete oxidation
of one glucose molecule using aerobic
respiration
Pathway
Glycolysis
Intermediate step
Krebs cycle
Total
ATP Produced
NADH
Produced
FADH2
Produced
ATP produced from complete oxidation of
one glucose using aerobic respiration
Pathway
By Substrate-Level
Phosphorylation
By Oxidative Phosphorylation
From NADH
Glycolysis
Intermediate step
Krebs cycle
Total
From FADH
Carbohydrate Catabolism
• 36 ATPs are produced in eukaryotes
Pathway
By Substrate-Level
Phosphorylation
By Oxidative Phosphorylation
From NADH
From FADH
0
Glycolysis
2
6
Intermediate step
0
6
Krebs cycle
2
18
4
Total
4
30
4
Catabolism of Other Compounds
• Polysaccharides and disaccharides
–Amylases for digestion of ___________ (very
common)
–Cellulase for digestion of cellulose (only
bacteria and fungi have this enzyme)
–Disaccharidases
• Lipid catabolism not covered
Protein Catabolism
Protein
Extracellular proteases
Deamination, decarboxylation, dehydrogenation,
desulfurylation
Amino acids
Organic acid
Decarboxylation
Krebs cycle
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 same organic
compound as energy source and carbon source.
Most medically important bacteria.
• Saprophytes vs. parasites
Anabolic Pathways
Biosynthesis not covered,
except for
Protein biosynthesis (see Ch 8)