Metabolism Part I: Fermentations Part II: Respiration

Learning objectives are to gain an appreciation of: Catabolism and anabolism ATP Generation and energy conservation Fermentation

Importance of Metabolism Images: (1) (2) en.wikipedia.org Industrial –Yogurt, cheese –Bread, wine, beer Medical/Health –Strain identification –Digestion Environmental –Cycling of elements –Pollutant transformation

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: –

Cell components nutrients + C-source chemicals or light

Two parts of metabolism Anabolism- synthesis of complex molecules from simpler ones during which energy is added as input Catabolism- the breakdown of larger, more complex molecules into smaller, simpler ones, during which energy is released, trapped, and made available for work

Anabolism and Growth Appropriate nutrients: –Carbon source –N, S, P sources –Trace metals Appropriate environmental conditions: –pH –Oxygen –Temperature. –Light

CO 2 Autotroph Organic Compounds Heterotroph Anabolism (biosynthesis) Carbons Sources

Catabolism Organotrophs Phototrophs Litotrophs Chemotrophs Organic compounds, i.e., glucose, succinate Inorganic compounds, S, Fe 2+,CO 2, H 2, CH 4 LightChemical compounds ATP, pmf Energy Sources:

Adenosine triphosphate two of the phosphate bonds are high energy bonds breaking bond to remove phosphate releases energy Figure 5.6 ATP and Energy

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 the formation of ATP from ADP and Pi, and thus to restore the energy balance of the cell

ATP is produced by three processes: _________________ phosphorylation –Two reactions are coupled to make ATP. __________________ phosphorylation –Carried out by: –Requires: Photophosphorylation

Chemical-based ATP synthesis: Substrate level phosphorylation Respiration-linked phosphorylation

ADP obtains phosphate from metabolic intermediate molecule which has a high energy bond ATP is formed ATP synthesis by substrate-level phosphorylation 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

Embden Meyerhof Pathway a.k.a. glycolysis Major pathway for: Major pathway of: Widespread method of: The end result is the release of a small amount of energy –conserved as ATP through: –And fermentation end products.

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:

Energy Input Reductions ATP by SLP

Glucose + 6O 2 6CO 2 + 6H 2 O ∆G˚’= kJ/mol

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

NADH

Fermentation ATP production by substrate level phosphorylation

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 the substrates –NAD+ recycled Fermentation end products are generally secreted

Why is fermentation important? Ecologically important for decomposition of organic material in anaerobic environments Byproducts are usually energy rich and used by other microbes as energy/carbon sources Useful in food industry Digestion

Lots of fermentable carbon sources Substrate level P

Lactic Acid Fermentation: I Carried out by several groups of bacteria –Lactobacillus and Lactococcus Gram + No cytochromes Anaerobes Only use sugars

Lactic Acid Fermentation Key Reaction Fermentations have to maintain redox balance.

Lactic acid bacteria and dairy products These bacteria are used to to make cheese and yogurt from milk. Carbon/energy source in milk is lactose Lactose is hydrolyzed Causes pH to decrease Milk proteins coagulate ugars/lactose.gif

What happens to the lactate? Transported out by lactate symporter –Takes a proton out with it. Lactate is still a good carbon/energy source. Glucose  2 Lactate ∆G˚’= -196 kJ/mol Made 2 ATPs = +63 kJ/mol -133 kJ/mol left in lactate Wasted energy!

Lactic acid bacteria are wasteful or are they? They live in organic rich environments without oxygen They generate a proton gradient so more ATP can be made They make acid which inhibits competitors They can grow in low iron environments

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

Large complex polysaccharides Starch, cellulose: found in plant material Glycogen: found in animals Bacterium needs specific enzyme to break down the sugar chains into monomers –The enzymes are often secreted.

Some Complex Polysaccharides Cellulose Aerobic decomposition: myxobacteria cytophaga sporocytophaga Fermented by: some clostridia Starch Amylases in: Bacillus acidocaldarius Streptococcus bovis Bacteroides amylophilus glucanases

Polysaccharides and Catabolic Enzymes In many cases the sugar monomers are ultimately metabolized either by glycolysis or another pathway to generate pyruvate.

Fermentations products are not fully oxidized ∆G˚’ glucose >> 2 lactate + 2H + = -198 kJ/mol ∆G˚’ glucose + 6O 2 >> 6CO 2 + 6H 2 O = kJ/mol More energy can be conserved from glucose by oxidizing it to CO2

Cells do this by: Oxidative phosphorylation The tricarboxylic acid cycle Next Lecture The maximum energy stored in glucose can be conserved only when its complete oxidation is coupled to the reduction of an external electron accepting substrate.

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?