Bacterial metabolism Assist. Prof. Emrah Ruh NEU Faculty of Medicine Department of Medical Microbiology

Bacterial metabolism Metabolism: The sum of all chemical reactions within a living organism Metabolism  Catabolism + anabolism

Bacterial metabolism Catabolism: Chemical reactions that result in the breakdown of more complex organic molecules into simpler substances Release energy (ATP; stored and used to power anabolic chemical reactions)

Bacterial metabolism Anabolism: Chemical reactions in which simpler substances are combined to form more complex molecules Require energy (ATP)

Bacterial metabolism Catabolism + anabolism  Metabolism

Bacterial metabolism Adenosine Triphosphate (ATP)

Bacterial metabolism Adenosine Triphosphate (ATP) Energy (ATP) is required for the anabolic reaction ATP ADP P +

Bacterial metabolism Adenosine Triphosphate (ATP) Catabolic reactions release energy The energy is stored as ATP ATP ADP P +

Bacterial metabolism Energy production Oxidation-Reduction Reactions: Oxidation: the removal of one or more electrons from a substrate. Protons (H+) are often removed with the electrons Reduction of a substrate: its gain of one or more electrons

Bacterial metabolism Energy production Oxidation-Reduction (Redox) Reactions:

Bacterial metabolism Energy production Oxidation-Reduction (Redox) Reactions: Nicotinamide adenine dinucleotide (NAD+) is the oxidized form; NADH is the reduced form

Bacterial metabolism Energy production The generation of ATP: Energy released during certain metabolic reactions can be trapped to form ATP from ADP and phosphate Addition of a phosphate to a molecule is called phosphorylation

Bacterial metabolism Energy production (ATP generation) The generation of ATP: Oxidative phosphorylation Substrate-level phosphorylation Photophosphorylation Chemiosmosis

Bacterial metabolism Energy production (ATP generation) Oxidative phosphorylation: Energy is released as electrons are passed to a series of electron acceptors (an electron transport chain) and finally to O2 or another inorganic compound Energy released is utilized to make ATP by chemiosmosis

Bacterial metabolism Energy production (ATP generation) Substrate-level phosphorylation: A high-energy phosphate from a substrate in catabolism is added to ADP An enzyme transfers the phosphate group to ADP to form ATP

Bacterial metabolism Energy production (ATP generation) Photophosphorylation: Energy from light is trapped by chlorophyll, and electrons are passed through a series of electron acceptors (an electron transport chain)  Energy released during electron transfer is utilized to make ATP by chemiosmosis

Bacterial metabolism Energy production (ATP generation) Chemiosmosis: The energy from electron transfer through an electron transport chain drives proton pumps The proton pumps move protons to one side of the membrane, increasing the concentration on one side and decreasing the concentration on the other side

Bacterial metabolism Energy production (ATP generation) Chemiosmosis: The protons diffuse down their concentration gradient through a membrane channel that has enzymatic (ATPase) activity The energy of the protons moving through the channel drives phosphorylation of ADP to make ATP

Bacterial metabolism Energy production (ATP generation) The generation of ATP: Oxidative phosphorylation Substrate-level phosphorylation Photophosphorylation Chemiosmosis

Bacterial metabolism Energy production (ATP generation) The processes that use these mechanisms: Cellular respiration (aerobic, anaerobic) Fermentation Photosynthesis

Bacterial metabolism Energy production (ATP generation) Cellular respiration: ATP is generated by oxidation of organic molecules, the passage of electrons down an electron transport chain, and chemiosmosis The final electron acceptor: Aerobic  O2 Anaerobic  Inorganic molecules (NO3-, SO4-2, CO3-2,…)

Bacterial metabolism Energy production (ATP generation) Fermentation: The final electron acceptor is an organic molecule ATP production is accomplished by substrate- level phosphorylation 

Bacterial metabolism Energy production (ATP generation) Photosynthesis: ATP is generated by photophosphorylation Plants, algae, cyanobateria,...

Bacterial metabolism Energy production (ATP generation)

Bacterial metabolism Metabolic diversity among organisms Carbon source Autotrophs Heterotrophs Energy source Phototrophs Chemotrophs

Bacterial metabolism Metabolic diversity among organisms Carbon source Autotrophs Self-feeders; and use CO2 as a carbon source Heterotrophs Feed on others and use organic sources of carbon

Bacterial metabolism Metabolic diversity among organisms Energy source Phototrophs Use light as an energy source Chemotrophs Use redox reactions of organic or inorganic compounds as an energy source

Bacterial metabolism Metabolic diversity among organisms

Bacterial metabolism Metabolic diversity among organisms

Bacterial metabolism Carbohydrate catabolism Most of a cell’s energy is produced from the oxidation of carbohydrates Glucose is the most commonly used carbohydrate The two major types of glucose catabolism: Respiration  glucose is completely broken down Fermentation  glucose is partially broken down

Bacterial metabolism Carbohydrate catabolism

Bacterial metabolism Carbohydrate catabolism Oxidation of glucose Glycolysis (Embden-Meyerhof pathway) Pentose phosphate pathway Entner-Doudoroff pathway

Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway) Stage 1

Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway) The most common pathway for the oxidation of glucose Pyruvic acid is the end-product Two ATP and two NADH molecules are produced from one glucose molecule

Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway)

Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway)

Bacterial metabolism Carbohydrate catabolism Oxidation of glucose Glycolysis (Embden-Meyerhof pathway) Pentose phosphate pathway Entner-Doudoroff pathway

Bacterial metabolism Carbohydrate catabolism Oxidation of glucose

Carbohydrate catabolism Cellular respiration During respiration, organic molecules are oxidized  Energy is generated from the electron transport chain The final electron acceptor: Aerobic respiration  O2 Anaerobic respiration  Inorganic molecule

Carbohydrate catabolism Aerobic respiration Stage 2

Carbohydrate catabolism Aerobic respiration From one molecule of glucose, oxidation in the Krebs cycle produces six molecules of NADH, two molecules of FADH2, and two molecules of ATP

Carbohydrate catabolism Aerobic respiration The Krebs Cycle

Carbohydrate catabolism Aerobic respiration Stage 3 (Electron transport system)

Carbohydrate catabolism Aerobic respiration Electrons are brought to the electron transport chain by NADH The electron transport chain consists of carriers, including flavoproteins, cytochromes, and ubiquinones Electrons are passed from one carrier to the next, the energy is used to drive proton pumps

Carbohydrate catabolism Aerobic respiration Electron transport system

Carbohydrate catabolism Aerobic respiration Two NADH molecules from glycolysis Two NADH molecules from formation of acetyl CoA Six NADH molecules from Krebs cycle Two FADH molecules from Krebs cycle One NADH: Three ATP molecules One FADH: Two ATP molecules

Carbohydrate catabolism Aerobic respiration - Chemiosmosis Protons being pumped across the membrane generate proton motive force as electrons move through a series of acceptors or carriers Energy produced from movement of the protons back across the membrane is used by ATP synthase to make ATP from ADP and phosphate

Carbohydrate catabolism Aerobic respiration - Chemiosmosis Electron carriers: Eukaryotes  inner mitochondrial membrane Prokaryotes  plasma membrane

Carbohydrate catabolism Aerobic respiration - Summary Aerobic prokaryotes: 38 ATP molecules are produced from complete oxidation of a glucose molecule in glycolysis, the Krebs cycle, and the electron transport chain Eukaryotes: 36 ATP molecules are produced from complete oxidation of a glucose molecule

Carbohydrate catabolism Aerobic respiration - Summary Aerobic prokaryotes

Carbohydrate catabolism Summary Aerobic prokaryotes

Carbohydrate catabolism Anaerobic respiration The final electron acceptors: Inorganic molecules (eg, NO3-, SO4-2, and CO3-2) NO3- (nitrate) is reduced to NO2- (nitrite) SO4-2 (sulfate) is reduced to H2S (hydrogen sulfide) CO3-2 (carbonate) is reduced to CH4 (methane) The total ATP yield is less than in aerobic respiration (only part of the Krebs cycle operates)

Carbohydrate catabolism Fermentation

Carbohydrate catabolism Fermentation Releases energy from sugars or other organic molecules by oxidation Does not require O2, the Krebs cycle, or an electron transport chain Can sometimes occur in the presence of O2 Uses an organic molecule as the final electron acceptor

Carbohydrate catabolism Fermentation Produces two ATP molecules by substrate-level phosphorylation Electrons removed from the substrate reduce NAD+ to NADH NADH molecules are then oxidized to NAD for lactic acid or alcohol fermentation Fermentation without aerobic electron transport and a complete Krebs cycle produces only two ATP molecules per glucose

Carbohydrate catabolism Fermentation

Carbohydrate catabolism Fermentation

Carbohydrate catabolism Fermentation Lactic acid fermentation Alcohol fermentation

Carbohydrate catabolism Fermentation

Carbohydrate catabolism Fermentation Lactic acid fermentation: Pyruvic acid is reduced by NADH to lactic acid Lactic acid fermenters include bacteria (eg, Streptococcus and Lactobacillus) Making milk into yogurt and cheese! Lactic acid can be fermented to propionic acid and CO2 by Propionibacterium freudenreichii (Swiss cheese)

Carbohydrate catabolism Fermentation Alcohol fermentation: Acetaldehyde is reduced by NADH to produce ethanol Alcohol fermenters include yeasts and bacteria Making wine, whiskey, bread, etc…! Ethanol can be fermented to acetic acid (vinegar) by Acetobacter Acetic acid can be fermented to methane by Methanosarcina

Carbohydrate catabolism ATP yield – Summary According to the quantity of ATP yield: Aerobic respiration Anaerobic respiration Fermentation Energy

Carbohydrate catabolism ATP yield – Summary

Bacterial metabolism Grouping  Carbohydrate utilization Type of carbohydrate utilization: Oxidative bacteria Fermentative bacteria Nonsaccharolytic bacteria (lipid and protein catabolism)

Bacterial metabolism Lipid and protein catabolism Lipids: Lipases hydrolyze lipids into glycerol and fatty acids Catabolic products can be further broken down in glycolysis and the Krebs cycle

Bacterial metabolism Lipid and protein catabolism Amino acids: Transamination (transfer of NH2), decarboxylation (removal of COOH), and dehydrogenation (H2) reactions convert the amino acids into substances (alkaline conditions) Catabolized substances enter the glycolytic pathway or Krebs cycle

Bacterial metabolism Lipid and protein catabolism

Bacterial metabolism Anabolism Polysaccharide biosynthesis Lipid biosynthesis Amino acid and protein biosynthesis Purine and pyrimidine biosynthesis

Anabolism Polysaccharide biosynthesis Glucose (and other simple sugars - monosaccharides) may be synthesized from intermediates in glycolysis and the Krebs cycle  Monosaccharides can be linked together to make polysaccharides

Anabolism Polysaccharide biosynthesis (Adenosine diphosphoglucose) (Uridine diphosphoglucose) (UDP-N-acetylglucosamine)

Anabolism Lipid biosynthesis Lipids are synthesized from fatty acids and glycerol

Anabolism Lipid biosynthesis

Anabolism Amino acid and protein biosynthesis Amino acids are required for protein biosynthesis All amino acids can be synthesized either directly or indirectly from intermediates of carbohydrate metabolism, particularly from the Krebs cycle Transamination or amination reactions: Amino acid = Organic acids + an amine (NH2) group

Anabolism Amino acid and protein biosynthesis

Anabolism Amino acid and protein biosynthesis Glutamic acid  a-Ketoglutaric acid + NH2 Aspartic acid  Oxaloacetic acid + NH2

Anabolism 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 (aspartic acid, glycine, glutamic acid) form the backbones of the purines and pyrimidines Includes DNA, RNA, ATP, NAD,…

Anabolism Purine and pyrimidine biosynthesis

Bacterial metabolism The integration of metabolism Anabolic and catabolic reactions are integrated through a group of common intermediates Such integrated metabolic pathways are referred to as amphibolic pathways

Bacterial metabolism