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
P
+
ADP
ATP
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
 Fermentation
Carbohydrate catabolism
Fermentation
 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