2Metabolic PathwaysM : a complete set of chemical reactions that occur in living cells, allowing cells to grow and reproduce, maintain their structures, and respond to their environments.Major challenges in bioprocess development:To select an organism that can efficiently make a given productordigest wastes in the Environment.It is important to understand the metabolic pathways.
3Metabolic Pathways - Overview of metabolism pathways Metabolism can be subdivided by- C : The intracellular process of degrading a compound into smaller and simpler products and generating energy.Glucose to CO2, and H2O, protein to amino acids.- A : the synthesis of more complex compounds and requires energy.Synthesis of small molecules (amino acids, nucleotides, fatty acids and sugars) and complex compounds (glycan (polysaccharide), DNA, RNA, and lipids.)
4Major Metabolic Pathways in a Bacterial Cell (M.Shuler, 2002) End products are formed and released from the cells through these reactions,which are often valuable products for human or animal consumption.e.g. ethanol, amino acids, enzymes, fatty acids, antibodies.
5Metabolic Pathways Bioenergetics Sunlight Photosynthesis by autotrophs :CO2 + H2O → carbohydratesAutotrophsor heterotrophsCatabolismgenerating energy,e.g ATPAnabolismrequiring energy
6Metabolic Pathways Bioenergetics - Energy is mainly stored or transferred by adenosine triphosphate (ATP).Other energy carrying compounds include GTP, UTP and CTP.Guanosine Triphospohate, Uridine triphosphate and cytidine triphosphate
7Metabolic Pathways Bioenergetics - Reducing power: supply hydrogen atom in biosynthesis.Nicotinamide Adenine Dinucleotide (NADH)Flavin Adenine Dinucleotide (FADH2)NADH and FADH2 are major electron carriers in the oxidation of fuel molecules and for ATP generation.Nicotinamide Adenine Dinucleotide Phosphate (NADPH).major electron donor in reductive biosynthesis, e.g photosynthesis
14Glucose Catabolism Glycolysis Glycolysis or Embden-Meyerhof-Parnas (EMP)Breakdown of a molecule of g to two pyruvate molecules.- Each pathway is catalyzed by particular enzyme(s)- Generating 2 ATP, 2 NADH and pyruvate (Key Metabolite).- Taking place in cytoplasm
19Glucose Catabolism Krebs, Tricarboxylic Acid (TCA), or Citric Acid Cycle Under a conditionsTaking place- in mitochondria in eucaryotes- associated with membrane-bound enzymes in procaryotesPyruvate produced in glycolysis (EMP) pathway transfer its reducing power to NAD+.
20Citric Acid Cycle amino acid synthesis Control site by ATP NADH generatedCO2 releasedFADH2 generatedamino acid synthesis
21Glucose Catabolism Citric Acid Cycle The overall reaction of TCA cycle:acetyl-CoA + 3 NAD + FAD + Pi + 2H2O → CoA + 3(NADH + H+) FADH2+GTP+ 2CO2Intermediate products such as oxylacetate and α–ketoglutarate are used as precursors for the synthesis of certain amino acids.The reducing power (NADH + H+ and FADH2) is used for biosynthesis pathway or for ATP generation through the electron transport chain.
23Glucose Catabolism Respiratory Chain-Oxidative Phosphorylation “Oxidative Phosphorylation is the electron transport chain that forms ATP as electrons are transferred from NADH or FADH2 to o by a series of electron carriers” (L. Stryer, 1988)- electron acceptor: oxygen (aerobic condition)- generate ATP, H2O- from NADH or FADH2Taking place in mitochondria in eucaryotesor in cytoplasmic membrane in procaryotes
24Glucose Catabolism Oxidative Phosphorylation In the process of Oxidative PhosphorylationIn eucaryotes:NADH + H ATPFADH ATPIn procaryotes:NADH + H ≤2 ATPFADH2 ATP
28Hydrocarbon Catabolism Hydrocarbon: C & H- Aliaphatic hydrocarbone.g. octane, C8H18polyethylene –HC=CH-- Aromatic hydrocarbonnaphthaleneMetabolism of hydrocarbon- Requires oxygen- Hydrocarbons are converted to acetyl-CoA which is metabolized by TCA cycle.- Challenges : low solubility in aqueous solution.available microorganisms are limitedPseudomonas, Mycobacterianaphthalene
29Nitrogen Compounds Catabolism Nitrogen compounds can be used for C, N and energy sourcesProteins → peptides → amino acids → converted to other amino acids or organic acids and ammonia by deamination.- organic acids: acetyl-CoA into TCA cycle, lipids- amino acids: proteins, other amino acids or enter TCA cycle- ammonium: amino acid, protein, nucleic acidsNucleic acids → ribose/deoxyribose, phosphoric acid and purine/pyrimidine- sugar: glycolysis and TCA- Phosphoric acid: ATP, lipids, nucleic acids- bases: nucleic acids, urea, acetic acids
33Summary of Metabolism Pathways - catabolism: ATP, C skeleton for further biosynthesis- anabolism: biosynthesis requiring energyBioenergetics:- energy storage and carrier ATP- Reducing power carriers: NADH, NADPH, FADH