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MetabolismPart I: Fermentations
Part II: Respiration
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Learning objectives are to gain anappreciation of:
Catabolism and anabolism
ATP Generation and energyconservation
Fermentation
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Importance of Metabolism
Images: (1) www.bact.wisc.edu (2) en.wikipedia.org
Industrial Yogurt, cheese Bread, wine, beer
Medical/Health
Strain identification Digestion
Environmental
Cycling of elements Pollutant transformation
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Metabolism: the bigger picture
What is metabolism? Chemical reactions that occur in living
organisms in order to maintain life.
What does maintain life mean? Growth and division
Maintaining cellular structures
Sense/respond to environment
Two parts of metabolism:
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Cell components
nutrients + C-source
chemicals or light
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Two parts of metabolism
Anabolism- synthesis of complex moleculesfrom simpler ones during which energy isadded as input
Catabolism- the breakdown of larger, morecomplex molecules into smaller, simplerones, during which energy is released,
trapped, and made available for work
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Anabolism and Growth
Appropriate nutrients: Carbon source
N, S, P sources
Trace metals
Appropriate environmental conditions: pH
Oxygen Temperature.
Light
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CO2
Autotroph
Organic Compounds
Heterotroph
Anabolism
(biosynthesis)
Carbons Sources
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Catabolism
Organotrophs
Phototrophs
Litotrophs
Chemotrophs
Organic compounds,
i.e., glucose, succinate
Inorganic compounds,
S, Fe2+,CO2, H2, CH4
LightChemical compounds
ATP, pmf
Energy Sources:
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Adenosine triphosphate
two of the phosphatebonds are high energy
bonds breaking bond to
remove phosphatereleases energy
Figure 5.6
ATP and Energy
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The Role of ATP in Metabolism
Reactions in which the terminal phosphate of ATP is
removed results in a:
Exergonic breakdown of ATP can be coupled with:
Energy conserving reactions are used to catalyze theformation of ATP from ADP and Pi, and thus to
restore the energy balance of the cell
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Chemical-based ATP synthesis:
Substrate level phosphorylation Respiration-linked phosphorylation
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ADP obtains phosphate from
metabolic intermediate
molecule which has a high
energy bond
ATP is formed
ATP synthesis by substrate-levelphosphorylation
Phosphorylated intermediates are generated in:
Glycolysis (Embden-Meyhof pathway)
Tricarboxylic Acid Cycle (TCA)
Fermentation Finally, the Pi is transferred from a high energy
phosphorylated intermediate to ADP by a kinase
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Embden Meyerhof Pathwaya.k.a. glycolysis
Major pathway for:
Major pathway of:
Widespread method of:
The end result is the release of a small amount ofenergy
conserved as ATP through:
And fermentation end products.
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Glycolysis and Fermentation
Glycolysis is an anoxic process
It is divided into two major stages
Nets two ATPs and two NADHs
End product of glycolysis is:
The fate of this metabolite varies:
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Energy Input
Reductions
ATP by SLP
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Glucose + 6O2 6CO2 + 6H2O G=-2830 kJ/mol
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Glycolysis and NADH
Glycolysis also generates NADH
But, cells need:
Fermentation can regenerate: This can be done through:
Substrates can be reduced by NADH
Example:Lactic acid
fermentation
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NADH
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Fermentation
ATP production by substrate
level phosphorylation
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What is fermentation?
Widespread method of anaerobic metabolism The end result is the release of a small amount of
energy conserved as ATP through substrate level
phosphorylation
Incomplete oxidation of substrates Need to have a fermentation balance
Oxidation-reduction state of products equal thesubstrates
NAD+ recycled
Fermentation end products are generally secreted
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Why is fermentation important?
Ecologically important for decomposition oforganic material in anaerobic environments
Byproducts are usually energy rich and
used by other microbes as energy/carbonsources
Useful in food industry
Digestion
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Lots of fermentable
carbon sources
Substrate level P
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Lactic Acid Fermentation: I
Carried out by several groups ofbacteria
Lactobacillus and
Lactococcus Gram +
No cytochromes
Anaerobes Only use sugars
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Lactic AcidFermentation
Key Reaction
Fermentations have
to maintain redox
balance.
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Lactic acid bacteria and dairyproducts
These bacteria are used to to make cheeseand yogurt from milk.
Carbon/energy source in milk is lactose
Lactose is hydrolyzed
Causes pH to decrease
Milk proteins coagulateQuickTime and a
TIFF (Uncompressed) decompressorare needed to see this picture.
http://web.mit.edu/esgbio/www/lm/s
ugars/lactose.gif
QuickTime and aTIFF (Uncompressed) decompressor
are needed to see this picture.
http://www.reluctantgourmet.com/images/cheese.jpg
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What happens to the lactate?
Transported out by lactate symporter Takes a proton out with it.
Lactate is still a good carbon/energysource.
Glucose 2 Lactate G= -196 kJ/molMade 2 ATPs = +63 kJ/mol
-133 kJ/mol left in lactate
Wasted energy!
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Lactic acid bacteria are wastefulor are they?
They live in organic rich environmentswithout oxygen
They generate a proton gradient so moreATP can be made
They make acid which inhibits competitors
They can grow in low iron environments
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Substrates other than glucose
Monosaccharides Fructose, mannose, galactose get
converted to glucose-6-phosphate or
fructose-6-phosphate Disaccharides--get cleaved in
monosaccharides by specific enzymes Lactose => galactose and glucose Maltose => 2 glucoses Sucrose => glucose and fructose
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Large complex polysaccharides
Starch, cellulose: foundin plant material
Glycogen: found in
animals Bacterium needs
specific enzyme tobreak down the sugarchains into monomers The enzymes are often
secreted.
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Some Complex Polysaccharides
CelluloseAerobic decomposition:myxobacteriacytophagasporocytophaga
Fermented by:some clostridia
StarchAmylases in:
Bacillus acidocaldariusStreptococcus bovisBacteroides amylophilus
glucanases
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Polysaccharides and Catabolic Enzymes
In many cases the sugar monomers are ultimately metabolized
either by glycolysis or another pathway to generate pyruvate.
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Fermentations products are not fully oxidized
G glucose >> 2 lactate + 2H+ = -198 kJ/mol
G glucose + 6O2
>> 6CO2
+ 6H2O = -2830 kJ/mol
More energy can be conservedfrom glucose by oxidizing it to CO2
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Cells do this by:
Oxidative phosphorylation The tricarboxylic acid cycle
Next Lecture
The maximum energy stored in glucose can beconserved only when its complete oxidation iscoupled to the reduction of an external electron
accepting substrate.
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Study Questions
1. How is ATP produced when organisms grow fermentatively?Does it matter what type of fermentation is occurring?
2. Why is pyruvate reduced in fermentations? To what can it be
reduced? What do the fermentation products have in common?
3. Do fermentations produce a lot of ATP? Why not? What types
of environments might fermentative bacteria (such as lactic acid
bacteria) do well in?
4. What are the roles of ATP and NAD+ in glycolysis?
5. Compare and contrast the metabolism of lactose or maltose with
that of glucose?6. Can molecules such as cellulose enter gram + cells? Gram
cells? Why/why not? If not, how are they consumed?