Microbial Metabolism Flashcards
Commercially or medically important bacterial products
Lactococcus and Lactobacillus, Streptococcus mutants
Important in laboratory
Escherichia coli, Klebsiella, Enterobacter
Importance of Microbial Metabolism
-Model for studying metabolic pathways and processes in eukaryotic cells
-Potential targets for antimicrobial drugs
All chemical changes occurring in a
microorganism during its growth and
development for healthy and stable
maintenance
Microbial Metabolism
Two classes of chemical reactions
-Anabolism
-Catabolism
Release free energy and reducing power that are captured in the form of ATP and NADPH, respectively.
Oxidative, exergonic pathways of catabolism
Consuming chemical energy in the form of ATP and using NADPH as a source of high energy electrons for reductive purposes.
Anabolic process, endergonic
Transfer energy from ATP to complex molecules
Anabolic reactions
Transfer energy from complex molecules to ATP
Catabolic reactions
Metabolic pathways are a series of reactions catalyzed by:
Multiple enzymes
Energy and Carbon Sources Used by
Different Groups of Prokaryotes
Photoautotroph, Photoheterotroph, Chemolithoautotroph, Chemoorganoheterotroph
Energy source: Sunlight
Carbon Source: Carbon dioxide
Photoautotroph
Energy Source: Sunlight
Carbon source: Organic compounds
Photoheterotroph
Energy source: Inorganic chemicals
Carbon Source: Carbon dioxide
Chemolithoautotroph
Energy source: Organic compounds
Carbon source: Organic compounds
Chemoorganoheterotroph
❑ “sugar splitting”
❑ occurs in cytosol of bacteria
❑ converts glucose (6-C) to pyruvate (3-C)
❑ can occur in the absence of oxygen
❑ enzyme-mediated
Glycolysis
- gross energy yield (Glycolysis) =
4 ATP + 2 NADH
- net energy yield (Glycolysis) =
2 ATP + 2 NADH
❑ phosphogluconate pathway or hexose monophosphate shunt
❑ other metabolic pathway used by cells to break down glucose
❑ generates NADPH, ribose 5-phosphate, and erythrose 4-phosphate
(intermediates)
Pentose Phosphate Pathway
❑ aerobic (O2-requiring) breakdown of nutrients with accompanying synthesis
of ATP
❑ comprises three stages in the metabolic breakdown of glucose
❑ takes place in the cytoplasm
Aerobic Respiration
three stages in the metabolic breakdown of glucose:
❑ transition step/conversion of pyruvate to acetyl CoA
❑ Krebs cycle / citric acid cycle
❑ oxidative phosphorylation: electron transport chain and chemiosmosis
❑ pyruvate converted to acetyl coenzyme A
❑ undergoes chemical modification/ “grooming”
Transition Step
Chemical Modification/”grooming”
❑ removal of carboxyl group from pyruvate and given off as CO2
❑ 2-C compound is oxidized, NAD+ is reduced to NADH
❑ coenzyme A joins the 2-C compound forming acetyl-coenzyme A (acetyl CoA)
Energy yield (per glucose in Transition Step):
2 NADH
Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle
Transition Reaction
❑ named after Hans Krebs
❑ also known as citric acid cycle or tricarboxylic acid cycle
❑ yields more energy than glycolysis
Krebs Cycle
❑ Energy yield (per glucose in Krebs cycle):
2 ATP +6 NADH + 2 FADH2
❑ final stage of cellular respiration
❑ “big energy payoff” stage
❑ uses electron transport chain and chemiosmosis
❑ located in the cell membrane
Oxidative Phosphorylation
membrane-embedded electron carriers that pass electrons sequentially from one to another
Electron transport chain
movement of ions (H+) down their electrochemical gradient that generates ATP
Chemiosmosis
Electron carriers (4)
❑ I – flavoprotein (flavin monunucleotide)
❑ II – Fe-S protein
❑ Quinone (Q)- non-protein mobile carrier ; aka CoQ
❑ Cytochrome (C) – mobile carrier; Q to oxygen
– enzyme
that makes ATP from
ADP and inorganic
phosphate
- uses energy of ion
gradient top power
ATP synthesis
ATP synthase
❑ varied types and arrangement of electron transport chain components
❑ could provide a mechanism to distinguish certain types of bacteria
Electron Transport Chain of Prokaryotes
Detects the presence of an enzyme “oxidase” produced by certain
bacteria which will reduce the dye – tetramethyl-p-phenylene diamine
dihydrochloride.
Oxidase Test
Positive test in Oxidase test is indicated by the development of a _________________
Purple Color
Oxidase positive:
Pseudomonas, Vibrio, Neisseria
Oxidase negative:
Salmonella, Shigella
Energy conversion:
1 NADH = 3ATP
1 FADH2 = 2 ATP
The balance sheet of aerobic respiration
(Glycolysis substrate-level phosphorylation)
2 ATP
The balance sheet of aerobic respiration
(Glycolysis NADH conversion (2 NADH))
6 ATP
The balance sheet of aerobic respiration
(Transition step (2 NADH))
6 ATP
The balance sheet of aerobic respiration
(Krebs cycle substrate-level phosphorylation)
2 ATP
The balance sheet of aerobic respiration
(Krebs cycle: NADH )
18 ATP
The balance sheet of aerobic respiration
(Krebs cycle: FADH2)
4 ATP
Total ATP in aerobic respiration
38 ATP
❑ oxygen is not the final electron acceptor in the electron transport chain
❑ less efficient form of energy transformation than aerobic respiration
❑ less amount of energy is released in the reduction of inorganic chemicals
other than molecular oxygen
❑ anaerobic or facultative bacteria
Anaerobic Respiration
Sulfate reduction
Desulfovibro
Carbon dioxide reduction
Methanobacterium and Methanococcus
❑ makes a few ATP molecules
❑ Krebs cycle and oxidative phosphorylation are shut down
❑ organic molecule accepts the electrons (not O2)
❑ i.e. E. coli (use any of the three ATP-generating options), LAB (obligate
fermenters), obligate anaerobes
Fermentation
process by which light energy is converted to chemical energy
Photosynthesis
Intermediary product of Photosynthesis in Microorganisms
ATP
Major end-product of Photosynthesis in Microorganisms
Glucose
❑ process takes place in cell membrane
* contains chlorophyll or chlorophyll-like pigments
* thylakoid membranes (cyanobacteria)
* chlorosomes (green bacteria)
* extensive cell membrane invaginations (purple bacteria)
Photosynthesis in Microorganisms
Prokaryotes
Green Sulfur bacteria, purple sulfur bacteria, cyanobacteria
Eukaryotes
Diatoms, dinoflagellates, algae
Photosynthesis occurs in the same manner as eukaryotic microorganisms
and green plants
Photosynthesis: Cyanobacteria
Mg-containing green pigment that absorbs light energy
chlorophyll a
Light-receiving systems
photosystems I and II
- chlorophylls and accessory pigments
- reaction center pigments
- antennae pigments
Photosystems I and II
Chlorophylls and accessory pigments
❑ bacteriochlorophylls
❑ carotenoids (photosymthetic prokaryotes and eukaryotes) and phycobilins (cyanobacteria and red algae)
purple and green photosynthetic bacteria
bacteriochlorophylls
electron donors in photosynthetic process
reaction center pigments
“funnel”, make up antenna complex
antennae pigments
❑ green sulfur bacteria and purple sulfur bacteria
❑ archaea (extreme halophiles)
Photosynthesis: Other Prokaryotes
❑ do not use water as source of hydrogen ions
❑ fatty acids and other organic or inorganic substances are used as source of H+ ions
❑ no oxygen is liberated
❑ anoxygenic
green sulfur bacteria and purple sulfur bacteria
bacteriorhodopsin pigment
archaea (extreme halophiles)
