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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?