Transcript Lecture 7

Chapter 5, part B
Microbial Metabolism
Overview of Respiration and Fermentation
Figure 5.11
Fermentation
• Fermentation releases energy from sugars or other organic molecules
by oxidation.
• Pyruvate is metabolized to various compounds
• O2 is not required in fermentation.
• Does not use the Krebs cycle or ETC
• Electrons removed from the substrate reduce
NAD+ to NADH.
• The final electron acceptor is an endogenous
organic molecule.
• Produces only small amounts of ATP (one or
two ATP molecules for each molecule of
starting material)
• ATP molecules are produced by substratelevel phosphorylation.
Fermentation
• Alcohol fermentation - acetaldehyde is
reduced by NADH to produce ethanol.
– Product - ethyl alcohol + CO2 (gas)
• Lactic acid fermentation (homolactic)pyruvic acid is reduced by NADH to
lactic acid.
– Product - lactic acid only
• Heterolactic fermentation
– Product - lactic acid as well as other acids
and alcohols.
Fermentation
Fermentation
Figure 5.18b
Lipid Catabolism
• Lipases hydrolyze lipids into
glycerol and fatty acids.
(hydrolase)
• Fatty acids and other
hydrocarbons are catabolized by
beta-oxidation.
• Catabolic products can be further
broken down in glycolysis and the
Krebs cycle.
Figure 5.20
Protein Catabolism
Extracellular proteases
Protein
Amino acids
Deamination, decarboxylation,
dehydrogenation
Organic acid
Urease
Urea
NH3 + CO2
Krebs cycle
Catabolism
Highly reduced
complex molecules
Oxidized
NAD+
NADH
Energy
ADP
ATP
Metabolic Pathways of Energy Use
Anabolism
• Polysaccharide Biosynthesis
ADPG (adenosine diphosphoglucose).
UGPG (uridine diphosphoglucose)
UDPNAc ( UDP-N-acetylglucoseamine)
Figure 5.28
Metabolic Pathways of Energy Use
• Lipid Biosynthesis
– Lipids are synthesized
from fatty acids and
glycerol.
• Glycerol is derived from
dihydroxyacetone
phosphate.
• Fatty acids are built from
acetyl CoA.
Figure 5.29
Metabolic Pathways of Energy Use
• Amino Acid and Protein Biosynthesis
• All amino acids can be synthesized either directly or indirectly
from intermediates of carbohydrate metabolism, particularly
from the Krebs cycle.
Figure 5.30a
Metabolic Pathways of Energy Use
• Purine and Pyrimidine Biosynthesis.
– The sugars composing nucleotides are derived from either
the pentose phosphate pathway or the Entner-Doudoroff
pathway.
– Carbon and nitrogen atoms
from certain amino acids form
the backbones of the purines
and pyrimidines
Figure 5.31
Reversible Reactions
• Can readily go in either direction.
• Each direction may need special conditions.
NADH
[Substrate concentration]
A + B


NAD+
[Product concentration]
AB
Amphibolic pathways
• Anabolic and catabolic reactions are
integrated through a group of
common intermediates.
• Both anabolic and catabolic
reactions also share some metabolic
pathways, such as Krebs
• Such integrated metabolic pathways
are referred to as amphibolic
pathways.
Phototrophs - Photosynthesis
•
Energy from sunlight is used to convert carbon dioxide( CO2) and
water (H2O) into organic materials to be used in cellular functions
such as biosynthesis and respiration
• Photo: Conversion of light energy into chemical energy (ATP)
– Light-dependent (light) reactions
• Synthesis: Fixing carbon into organic molecules
– Light-independent (dark) reaction, Calvin-Benson cycle
• Process is localized in chloroplasts (eukaryotes) or chlorosomes
(prokaryotes)
Light-dependent (light) reactions
Cyclic
Photophosphorylation
- the electrons return to
the chlorophyll
Noncyclic photophosphorylation The electrons are used to reduce
NADP+ and form NADPH
-The electrons from:
-H2O or H2S replace those lost from
chlorophyll
(H2S)
(S)
Figure 5.24a
Photosynthesis
• Oxygenic:
6CO2 + 12H2O + Light energy  C6H12O6 + 6 O2 + 6H2O
• Anoxygenic:
6CO2 + 12H2S + Light energy  C6H12O6 + 12 S + 6 H2O
Light-independent (dark) reaction
• Photosynthesis: Fixing carbon (CO2) into organic molecules
•
• Calvin-Benson cycle
• Use NADPH as cofactor
• Characteristic of:
- Cianobacteria,
- Green and Purple bacteria
- Algae and Plants
Autotrophs: Carbon dioxide (CO2) is used as source of carbon
Figure 5.25
A Summary of Energy Production Mechanisms
Nutritional types of organisms by Sources of energy
Chemotrophs: Bond energy is released from a chemical compound
Phototrophs: Light is absorbed in photo receptors and transformed into chemical
energy.
Chemoheterotrophs
• Chemotrophs - Organisms that use energy from organic chemicals
Glucose
NAD+
ETC
Pyruvic acid
NADH
ADP + P
ATP
• Heterotrophs: Organic compounds are metabolized to get carbon for
growth and development.
• Cannot fix carbon
Chemoautotrophs
• Use energy from inorganic chemicals
• Energy is used in the Calvin-Benson cycle to fix CO2
2Fe2+
NAD+
ETC
2Fe3+
NADH
2 H+
• Chemoautotroph
– Thiobacillus ferrooxidans
ADP + P
ATP
Phototrophs
• Use Energy from sunlight
Chlorophyll
ETC
Chlorophyll
oxidized
ADP + P
ATP
• Energy is used in the Calvin-Benson cycle to fix CO2 –
Photoautotrophs
• Energy is used in anabolism (carbon from organic compounds) Photoheterotrophs
A nutritional classification of organisms
Metabolic Diversity Among Organisms
Nutritional type
Energy
source
Carbon
source
Example
Photoautotroph
Light
CO2
Oxygenic:
Cyanobacteria
plants.
Anoxygenic: Green,
purple bacteria.
Green, purple
nonsulfur bacteria.
Photoheterotroph
Light
Organic
compounds
Chemoautotroph
Chemical CO2
Iron-oxidizing
bacteria.
Chemoheterotroph
Chemical Organic
compounds
Fermentative
bacteria.
Animals, protozoa,
fungi, bacteria.
Carbon cycle
Sulphur cycle
Nitrogen cycle
Phosphorus cycle
Biochemical tests and bacterial identification
Staphylococcus aureus
Pseudomonas aeruginosa
Gram stain
Bacillus subtilis
Kelbsiella pneumonia
• K. pneumonia and Ps. aeruginosa look alike through a
microscope after Gram stain; so how can they be differentiated?
Different species produce different enzymes
determine what type of
metabolic reactions an organism can carry out
– Oxygen requirements
– Fermentation of different substrates (sugars)
– Enzymes of respiration
– Amino acid catabolizing enzymes
Toxic Forms of Oxygen
• Singlet oxygen: O2 boosted to a higher-energy state
• Superoxide free radicals: O2–
• Peroxide anion: O22–
• Hydroxyl radical (OH)
Chemical Requirements Oxygen (O2)
Fermentation
test
Protein
Catabolism
•Fermentation tests are used to determine the substrates the
organism can metabolize by the products it generates.
E.coli
Control tube S.epidermidis S.aureus
Medium: Carbohydrate Mannitol, inverted Durham tube
Products: Acid and gas.
.
Figure 5.23
Protein Catabolism
Urease
NH3 + CO2
Dichotomous Key
• A dichotomous key is a series of questions which leads to the
identification of an item.
– a device on paper or computer that aids identification of a species or other
type of entity.
• Dichotomous keys are used for the identification of organisms.
• A dichotomous key works by
offering two alternatives at each
juncture, and the choice of one
of those alternatives determines
the next step.
Learning objectives
• Describe the chemical reactions of, and list some products of,
fermentation.
• Describe how lipids and proteins undergo catabolism.
• Provide two examples of the use of biochemical tests to identify
bacteria.
• Compare and contrast cyclic and noncyclic photophosphorylation.
• Compare and contrast the light-dependent and light-independent
reactions of photosynthesis.
• Compare and contrast oxidative phosphorylation and
photophosphorylation.
• Write a sentence to summarize energy production in cells.
• Categorize the various nutritional patterns among organisms according
to carbon source and mechanisms of carbohydrate catabolism and ATP
generation.
• Describe the major types of anabolism and their relationship to
catabolism.
• Define amphibolic pathways