Microbial Metabolism
Ch 5
• Metabolism is the sum of the
chemical reactions in an organism.
• Catabolism is the energy-releasing
processes.
• Anabolism is the energy-using
processes. (typically building
something)
Microbial Metabolism
• Catabolism provides the building blocks and
energy for anabolism.
Figure 5.1
Amphibolic pathways
• Are metabolic pathways that have both
catabolic and anabolic functions.
– This is basically all of life
Figure 5.32.1
Amphibolic pathways
Figure 5.32.2
• A metabolic pathway is a sequence of
enzymatically catalyzed chemical
reactions in a cell.
• A primary metabolic pathway are the
reactions that do the basic work of the
cell. Get food and grow
• Metabolic pathways are determined by
enzymes.
• Enzymes are encoded by genes.
Biochemical tests
• Used to
identify
bacteria.
• Enzymes
are genes
• Sum of
genes is
your
organism
Figure 10.8
Enzymes
Figure 5.2
Enzymes
• Biological catalysts
– Specific for a chemical reaction; not used up in
that reaction
• Apoenzyme: protein
• Cofactor: Nonprotein component
– Coenzyme: Organic cofactor
• Holoenzyme: Apoenzyme + cofactor
Enzymes
Figure 5.3
Important Coenzymes
•
•
•
•
•
•
•
NAD+
NADP+
FAD
Coenzyme A
Biotin
Folic acid
Many of the vitamins
Enzymes
• The turnover number is generally 1-10,000
molecules per second.
Figure 5.4
Factors Influencing Enzyme
Activity
• Enzymes can be denatured by temperature
and pH
Figure 5.6
•
Factors Influencing Enzyme
Activity
Temperature
Figure 5.5a
•
Factors Influencing Enzyme
Activity
pH
Figure 5.5b
Factors Influencing Enzyme
Activity
• Substrate concentration
Figure 5.5c
•
Factors Influencing Enzyme
Activity
Competitive
inhibition
Figure 5.7a, b
Factors Influencing Enzyme
Activity
Sulfa inhibits
the enzyme that
uses PABA for
synthesis of
folic acid
Factors Influencing Enzyme
Activity
• Noncompetitive inhibition
Figure 5.7a, c
• Feedback
inhibition
Figure 5.8
The Generation of ATP
• ATP is generated by the phosphorylation of
ADP.
The Generation of ATP
• Substrate-level phosphorylation is the
transfer of a high-energy PO4- to ADP.
The Generation of ATP
• Energy released from the transfer of
electrons (oxidation) of one compound to
another (reduction) is used to generate
ATP by chemiosmosis.
Metabolic Pathways
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
Preparatory
Stage
Glucose
1
• 2 ATPs are used
• Glucose is split
to form 2
Glyceraldehyde3-phosphate
Glucose
6-phosphate
2
Fructose
6-phosphate
3
4
Fructose
1,6-diphosphate
5
Glyceraldehyde
3-phosphate
(GP)
Dihydroxyacetone
phosphate (DHAP)
Figure 5.12.1
Energy-Conserving Stage
6
1,3-diphosphoglyceric acid
• 2 Glucose-3phosphate
oxidized to 2
Pyruvic acid
• 4 ATP
produced
• 2 NADH
produced
7
3-phosphoglyceric acid
8
2-phosphoglyceric acid
9
Phosphoenolpyruvic acid
(PEP)
10
Pyruvic acid
Figure 5.12.2
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
– Use and production of 5 carbon sugars (na)
– Bacillus subtilis, E. coli, Enterococcus faecalis
• 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 generated by oxidative
phosphorylation
Intermediate Step
• Pyruvic acid
(from glycolysis)
is oxidized and
decarboyxlated
Figure 5.13.1
Krebs Cycle
• Oxidation of acetyl CoA produces NADH
and FADH2
Krebs Cycle
Figure 5.13.2
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.
Chemiosmosis
Figure 5.15
Electron transport and
Chemiosmosis
Figure 5.16.2
Figure 5.14
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
cycles operations under anaerobic
conditions.
Anaerobic respiration
Electron acceptor
Products
NO3–
NO2–, N2 + H2O
SO4–
H2S + H2O
CO32 –
CH4 + H2O
• Energy produced from complete oxidation of
1 glucose using aerobic respiration
Pathway
ATP
produced
NADH
FADH2
produce produce
d
d
Glycolysis
2
2
0
Intermediate
step
0
2
Krebs cycle
2
6
2
Total
4
10
2
• ATP produced from complete oxidation of 1
glucose using aerobic respiration
Pathway
Glycolysis
Intermediate
step
Krebs cycle
Total
By substratelevel
phosphorylati
on
2
By oxidative
phosphorylation
From
From
NADH
FADH
6
0
0
6
2
18
4
4
30
4
• 36 ATPs are produced in eukaryotes.
Pathway
Eukaryote
Prokaryote
Glycolysis
Cytoplasm
Cytoplasm
Intermediate step
Cytoplasm
Cytoplasm
Krebs cycle
Mitochondrial
matrix
Mitochondrial
inner membrane
Cytoplasm
ETC
Plasma
membrane
Fermentation
• 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
Figure 5.18b
Fermentation
• Alcohol fermentation. Produces ethyl
alcohol + CO2
• Lactic acid fermentation. Produces
lactic acid.
– Homolactic fermentation. Produces lactic acid
only.
– Heterolactic fermentation. Produces lactic
acid and other compounds.
Fermentation
Figure 5.19
Fermentation
Production of acid and gas
Figure 5.23
Lipid Catabolism
Figure 5.20
Protein Catabolism
Protein
Extracellular proteases
Deamination, decarboxylation, dehydrogenation
Amino acids
Organic acid
Krebs cycle
• Used to
identify
bacteria.
Biochemical tests
Figure 10.8
• Halobacterium
uses
bacteriorhodopsi
n, not chlorophyll,
to generate
electrons for a
chemiosmotic
proton pump.
Chemotrophs
• Use energy from chemicals.
– Chemoheterotroph
Glucose
NAD+
ETC
Pyruvic acid
NADH
ADP + P
• Energy is used in anabolism.
ATP
Chemotrophs
• Use energy from chemicals.
– Chemoautotroph, Thiobacillus ferroxidans
2Fe2+
NAD+
ETC
2Fe3+
NADH
ADP + P
ATP
2 H+
• Energy used in the Calvin-Benson cycle to fix CO2.
Metabolic Diversity Among
Organisms
Nutritional type
Energy
source
Carbon
source
Example
Photoautotroph
Light
CO2
Oxygenic:
Cyanobacteria plants.
Anoxygenic: Green,
purple bacteria.
Organic
Green, purple
compounds nonsulfur bacteria.
Photoheterotroph
Light
Chemoautotroph
Chemical
CO
Chemoheterotroph
Chemical
Organic
Fermentative bacteria.
compounds Animals, protozoa,
fungi, bacteria.
Iron-oxidizing
bacteria.
Metabolic Pathways of Energy
Use
• Polysaccharide Biosynthesis
Figure 5.28
Metabolic Pathways of Energy
Use
• Lipid
Biosynthesis
Figure 5.29
Metabolic Pathways of Energy
Use
• Amino Acid and Protein Biosynthesis
Figure 5.30a
Metabolic Pathways of Energy
Use
•Amino Acid and Protein Biosynthesis
Figure 5.30b
Metabolic Pathways of Energy
Use
• Purine and
Pyrimidine
Biosynthesis
Figure 5.31
Amphibolic pathways
• Are metabolic pathways that have both
catabolic and anabolic functions.
Figure 5.32.1
Amphibolic pathways
Figure 5.32.2