PowerPoint® Lecture
Presentations prepared by
Mindy Miller-Kittrell,
North Carolina
State University
CHAPTER
5
Microbial
Metabolism
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• Metabolism
• Collection of controlled biochemical reactions that take
place within a microbe
• Ultimate function of metabolism is to reproduce the
organism
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• Metabolic Processes Guided by Eight Elementary
Statements
• Every cell acquires nutrients
• Metabolism requires energy from light or catabolism of
nutrients
• Energy is stored in adenosine triphosphate (ATP)
• Cells catabolize nutrients to form precursor metabolites
• Precursor metabolites, energy from ATP, and enzymes
are used in anabolic reactions
• Enzymes plus ATP form macromolecules
• Cells grow by assembling macromolecules
• Cells reproduce once they have doubled in size
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• Catabolism and Anabolism
• Two major classes of metabolic reactions
• Catabolic pathways
• Break larger molecules into smaller products
• Exergonic (release energy)
• Anabolic pathways
• Synthesize large molecules from the smaller products of
catabolism
• Endergonic (require more energy than they release)
© 2014 Pearson Education, Inc.
Figure 5.1 Metabolism is composed of catabolic and anabolic reactions.
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• Oxidation and Reduction Reactions
• Transfer of electrons from an electron donor to an electron
acceptor
• Reactions always occur simultaneously
• Cells use electron carriers to carry electrons (often in H atoms)
• Three important electron carriers
• Nicotinamide adenine dinucleotide (NAD+)
• Nicotinamide adenine dinucleotide phosphate (NADP+)
• Flavin adenine dinucleotide (FAD)
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• ATP Production and Energy Storage
• Organisms release energy from nutrients
• Can be concentrated and stored in high-energy phosphate bonds
(ATP)
• Phosphorylation – inorganic phosphate is added to substrate
• Cells phosphorylate ADP to ATP in three ways
• Substrate-level phosphorylation
• Oxidative phosphorylation
• Photophosphorylation
• Anabolic pathways use some energy of ATP by breaking a
phosphate bond
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• The Roles of Enzymes in Metabolism
• Enzymes are organic catalysts
• Increase likelihood of a reaction
© 2014 Pearson Education, Inc.
Enzymes: Overview
PLAY
© 2014 Pearson Education, Inc.
Enzymes: Overview
Basic Chemical Reactions Underlying
Metabolism
• The Roles of Enzymes in Metabolism
• Naming and classifying enzymes
• Six categories of enzymes based on mode of action
• Hydrolases
• Isomerases
• Ligases or polymerases
• Lyases
• Oxidoreductases
• Transferases
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• The Roles of Enzymes in Metabolism
• The makeup of enzymes
• Many protein enzymes are complete in themselves
• Apoenzymes are inactive if not bound to nonprotein
cofactors (inorganic ions or coenzymes)
• Binding of apoenzyme and its cofactor(s) yields
holoenzyme
• Some are RNA molecules called ribozymes
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Basic Chemical Reactions Underlying
Metabolism
• The Roles of Enzymes in Metabolism
• Enzyme activity
• Many factors influence the rate of enzymatic reactions
• Temperature
• pH
• Enzyme and substrate concentrations
• Presence of inhibitors
• Inhibitors
• Substances that block an enzyme's active site
• Do not denature enzymes
• Three types
© 2014 Pearson Education, Inc.
Figure 5.8 Denaturation of protein enzymes.
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Many organisms oxidize carbohydrates as primary
energy source for anabolic reactions
• Glucose most common carbohydrate used
• Glucose catabolized by two processes:
• Cellular respiration
• Fermentation
© 2014 Pearson Education, Inc.
Figure 5.12 Summary of glucose catabolism.
Respiration
G
L
Y
C
O
L
Y
S
I
S
Glucose
Fermentation
NADH
NADH
ATP
ATP
Pyruvic acid
(or derivative)
2 Pyruvic acid
Formation of
fermentation
end-products
Acetyl-CoA
FADH2
NADH
KREBS
CYCLE
e–
ATP
ADP
Electrons
© 2014 Pearson Education, Inc.
ATP
Final electron
acceptor
Carbohydrate Catabolism
• Glycolysis
• Occurs in cytoplasm of most cells
• Involves splitting of a six-carbon glucose into two three-
carbon sugar molecules
• Substrate-level phosphorylation – direct transfer of
phosphate between two substrates
• Net gain of two ATP molecules, two molecules of
NADH, and precursor metabolite pyruvic acid
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Glycolysis
• Divided into three stages involving 10 total steps
• Energy-investment stage
• Lysis stage
• Energy-conserving stage
© 2014 Pearson Education, Inc.
Figure 5.13 Glycolysis.
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Cellular Respiration
• Resultant pyruvic acid completely oxidized to produce
ATP by series of redox reactions
• Three stages of cellular respiration
1. Synthesis of acetyl-CoA
2. Krebs cycle
3. Final series of redox reaction
(electron transport chain)
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Cellular Respiration
• Synthesis of acetyl-CoA
• Results in
• Two molecules of acetyl-CoA
• Two molecules of CO2
• Two molecules of NADH
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Cellular Respiration
• The Krebs cycle
• Great amount of energy remains in bonds of acetyl-CoA
• Transfers much of this energy to coenzymes NAD+ and FAD
• Occurs in cytosol of prokaryotes and in matrix of
mitochondria in eukaryotes
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Cellular Respiration
• The Krebs cycle
• Six types of reactions in Krebs cycle
• Anabolism of citric acid
• Isomerization
• Redox reactions
• Decarboxylations
• Substrate-level phosphorylation
• Hydration reaction
© 2014 Pearson Education, Inc.
Figure 5.16 The Krebs cycle.
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Cellular Respiration
• The Krebs cycle
• Results in
• Two molecules of ATP
• Two molecules of FADH2
• Six molecules of NADH
• Four molecules of CO2
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Cellular Respiration
• Electron transport
• Most significant production of ATP occurs from series of
redox reactions known as an electron transport chain (ETC)
• Series of carrier molecules that pass electrons from one to
another to final electron acceptor
• Energy from electrons used to pump protons (H+) across the
membrane, establishing a proton gradient
• Located in cristae of eukaryotes and in cytoplasmic
membrane of prokaryotes
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Cellular Respiration
• Chemiosmosis
• Use of electrochemical gradients to generate ATP
• Cells use energy released in redox reactions of ETC
to create proton gradient
• Protons flow down electrochemical gradient through
ATP synthases that phosphorylate ADP to ATP
• Called oxidative phosphorylation because proton
gradient is created by oxidation of components of
ETC
• Total of ~34 ATP molecules formed from one
molecule of glucose
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Carbohydrate Catabolism
• Fermentation
• Sometimes cells cannot completely oxidize glucose by
cellular respiration
• Cells require constant source of NAD+
• Cannot be obtained simply using glycolysis and Krebs cycle
• Fermentation pathways provide cells with alternate source
of NAD+
• Partial oxidation of sugar (or other metabolites) to release
energy using an organic molecule from within the cell as final
electron acceptor
© 2014 Pearson Education, Inc.
Figure 5.22 Representative fermentation products and the organisms that produce them.
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Other Catabolic Pathways
• Lipids and proteins contain energy in their chemical
bonds
• Can be converted into precursor metabolites
• Serve as substrates in glycolysis and the Krebs cycle
© 2014 Pearson Education, Inc.
Figure 5.24 Protein catabolism.
Polypeptide
Proteases
Extracellular fluid
Amino acids
Cytoplasmic
membrane
Deamination
Cytoplasm
To Krebs cycle
© 2014 Pearson Education, Inc.
Photosynthesis
• Many organisms synthesize their own organic
molecules from inorganic carbon dioxide
• Most of these organisms capture light energy and
use it to synthesize carbohydrates from CO2 and
H2O by a process called photosynthesis
© 2014 Pearson Education, Inc.
Photosynthesis
• Chemicals and Structures
• Chlorophylls
• Important to organisms that capture light energy with
pigment molecules
• Composed of hydrocarbon tail attached to lightabsorbing active site centered on magnesium ion
• Active sites structurally similar to cytochrome
molecules in ETC
• Structural differences cause absorption at different
wavelengths
© 2014 Pearson Education, Inc.
Photosynthesis
• Chemicals and Structures
• Photosystems
• Arrangement of molecules of chlorophyll and other pigments to
form light-harvesting matrices
• Embedded in cellular membranes called thylakoids
• In prokaryotes – invagination of cytoplasmic membrane
• In eukaryotes – formed from inner membrane of chloroplasts
• Arranged in stacks called grana
• Stroma is space between outer membrane of grana and thylakoid
membrane
© 2014 Pearson Education, Inc.
Photosynthesis
• Chemicals and Structures
• Two types of photosystems
• Photosystem I (PS I)
• Photosystem II (PS II)
• Photosystems absorb light energy and use redox
reactions to store energy in the form of ATP and NADPH
• Light-dependent reactions depend on light energy
• Light-independent reactions synthesize glucose from
carbon dioxide and water
© 2014 Pearson Education, Inc.
Photosynthesis
• Light-Dependent Reactions
• As electrons move down the chain, their energy is used
to pump protons across the membrane
• Photophosphorylation uses proton motive force to
generate ATP
• Photophosphorylation can be cyclic or noncyclic
© 2014 Pearson Education, Inc.
Photosynthesis
• Light-Independent Reactions
• Do not require light directly
• Use ATP and NADPH generated by light-dependent
reactions
• Key reaction is carbon fixation by Calvin-Benson cycle
• Three steps
• Fixation of CO2
• Reduction
• Regeneration of RuBP
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Figure 5.29 The role of gluconeogenesis in the biosynthesis of complex carbohydrates.
© 2014 Pearson Education, Inc.
Figure 5.30 Biosynthesis of fat, a lipid.
© 2014 Pearson Education, Inc.
Integration and Regulation of Metabolic
Function
• Cells synthesize or degrade channel and transport
proteins
• Cells often synthesize enzymes only when
substrate is available
• Cells catabolize the more energy-efficient choice if
two energy sources are available
• Cells synthesize metabolites they need, cease
synthesis if metabolite is available
© 2014 Pearson Education, Inc.
Integration and Regulation of Metabolic
Function
• Eukaryotic cells isolate enzymes of different
metabolic pathways within membrane-bounded
organelles
• Cells use allosteric sites on enzymes to control
activity of enzymes
• Feedback inhibition slows/stops anabolic
pathways when product is in abundance
• Cells regulate amphibolic pathways by requiring
different coenzymes for each pathway
© 2014 Pearson Education, Inc.
Integration and Regulation of Metabolic
Function
• Two types of regulatory mechanisms
• Control of gene expression
• Cells control amount and timing of protein (enzyme)
production
• Control of metabolic expression
• Cells control activity of proteins (enzymes) once produced
© 2014 Pearson Education, Inc.