1 Chapter 10 Catabolism : Energy Release and Conservation
CHAPTER GLOSSARY Aerobic respiration Anaerobic respiration
Anoxygenic photosynthesis ATP synthase Bacteriochlorophyll
Bacteriorhodopsin Chemiosmotic hypothesis Chemolithotroph
Chlorophyll Cyclic photophosphorylation Dark reactions
Embden-Meyerhof pathway Entner-Doudoroff pathway Fermentation
Glycolysis Light reactions Noncyclic photophosphorylation Oxidative
phosphorylation Oxygenic photosynthesis Pentose phosphate pathway
Photophosphorylation Photosynthesis Proton motive force (PMF)
Substrate-level phosphorylation Tricarboxylic acid (TCA) cycle
Slide 2 2 Chemoorganotrophic fueling processes also called
chemoheterotrophs processes aerobic respiration anaerobic
respiration fermentation Slide 3 3 Chemoorganic fueling
processes-respiration most respiration involves use of an electron
transport chain as electrons pass through the electron transport
chain to the final electron acceptor, a proton motive force (PMF)
is generated and used to synthesize ATP aerobic respiration final
electron acceptor is oxygen anaerobic respiration final electron
acceptor is different exogenous acceptor such as NO 3-, SO 4 2-, CO
2, Fe 3+, or SeO 4 2- organic acceptors may also be used ATP made
primarily by oxidative phosphorylation Slide 4 4 Chemoorganic
fueling processes - fermentation uses an endogenous electron
acceptor usually an intermediate of the pathway used to oxidize the
organic energy source e.g., pyruvate does not involve the use of an
electron transport chain nor the generation of a proton motive
force ATP synthesized only by substrate-level phosphorylation Slide
5 5 Energy Sources many different energy sources are funneled into
common degradative pathways most pathways generate glucose or
intermediates of the pathways used in glucose metabolism few
pathways greatly increase metabolic efficiency Slide 6 6 Amphibolic
Pathways function both as catabolic and anabolic pathways important
ones Embden-Meyerhof pathway pentose phosphate pathway
tricarboxylic acid (TCA) cycle Catabolic Pathways enzyme catalyzed
reactions whereby the product of one reaction serves as the
substrate for the next pathways also provide materials for
biosynthesis amphibolic pathways Slide 7 7 Aerobic Respiration
process that can completely catabolize an organic energy source to
CO 2 using glycolytic pathways (glycolysis) TCA cycle electron
transport chain with oxygen as the final electron acceptor produces
ATP, and high energy electron carriers Slide 8 8 The Breakdown of
Glucose to Pyruvate Three common routes Embden-Meyerhof pathway
Entner-Doudoroff pathway pentose phosphate pathway The
Embden-Meyerhof Pathway glucose + 2ADP + 2P i + 2NAD + 2 pyruvate +
2ATP + 2NADH + 2H + occurs in cytoplasmic matrix of most
microorganisms, plants, and animals the most common pathway for
glucose degradation to pyruvate in stage two of aerobic respiration
function in presence or absence of O 2 two phases Slide 9 9
addition of phosphates primes the pump oxidation step generates
NADH high-energy molecules used to synthesize ATP by
substrate-level phosphorylation The Embden-Meyerhof Pathway Slide
10 10 The Entner-Doudoroff Pathway yield per glucose molecule: 1
ATP 1 NADPH 1 NADH reactions of Embden- Meyerhof Pathway reactions
of Entner- Doudoroff Pathway used by soil bacteria and a few
gram-negative bacteria replaces the first phase of the
Embden-Meyerhof pathway Slide 11 11 The Pentose Phosphate Pathway
also called hexose monophosphate pathway can operate at same time
as glycolytic pathway or Entner-Doudoroff pathway can operate
aerobically or anaerobically an amphibolic pathway glucose-6-P +
12NADP + + 7H 2 O 6CO 2 + 12NADPH + 12H + P i Summary of pentose
phosphate pathway Slide 12 12 Oxidation steps Produce NADPH, which
is needed for biosynthesis sugar trans- formation reactions produce
sugars needed for biosynthesis sugars can also be further degraded
The Pentose Phosphate Pathway Slide 13 13 The Tricarboxylic Acid
Cycle also called citric acid cycle and Krebs cycle common in
aerobic bacteria, free-living protozoa, most algae, and fungi major
role is as a source of carbon skeletons for use in biosynthesis for
each acetyl-CoA molecule oxidized, TCA cycle generates: 2 molecules
of CO 2 3 molecules of NADH one FADH 2 one GTP Slide 14 14 Electron
Transport and Oxidative Phosphorylation only 4 ATP molecules
synthesized directly from oxidation of glucose to CO 2 most ATP
made when NADH and FADH 2 (formed as glucose degraded) are oxidized
in electron transport chain (ETC) Electron Transport Chains the
mitochondrial electron transport chain (ETC) is composed of a
series of electron carriers that operate together to transfer
electrons from NADH and FADH 2 to a terminal electron acceptor, O 2
electrons flow from carriers with more negative reduction
potentials (E 0 ) to carriers with more positive E 0 Slide 15 15
The Electron Transport Chain large difference in E 0 of NADH and E
0 of O 2 large amount of energy released each carrier is reduced
and then reoxidized carriers are constantly recycled the difference
in reduction potentials electron carriers, NADH and O 2 is large,
resulting in release of great deal of energy Slide 16 16
Mitochondrial ETC in eukaryotes the electron transport chain
carriers are within the inner mitochondrial membrane and connected
by coenzyme Q and cytochrome c electron transfer accompanied by
proton movement across inner mitochondrial membrane Slide 17 17
located in plasma membrane some resemble mitochondrial ETC, but
many are different different electron carriers may be branched may
be shorter may have lower P/O ratio Bacterial and Archaeal ETCs
Paracoccus denitrificans facultative, soil bacterium extremely
versatile metabolically under oxic conditions, uses aerobic
respiration similar electron carriers and transport mechanism as
mitochondria protons transported to periplasmic space rather than
inner mitochondrial membrane can use one carbon molecules instead
of glucose Slide 18 18 upper branch stationary phase and low
aeration lower branch log phase and high aeration Electron
Transport Chain of E. coli branched pathway Different array of
cytochromes used than in mitochondrial Slide 19 19 Oxidative
Phosphorylation Process by which ATP is synthesized as the result
of electron transport driven by the oxidation of a chemical energy
source Chemiosmotic hypothesis the most widely accepted hypothesis
to explain oxidative phosphorylation electron transport chain
organized so protons move outward from the mitochondrial matrix as
electrons are transported down the chain proton expulsion during
electron transport results in the formation of a concentration
gradient of protons and a charge gradient the combined chemical and
electrical potential difference make up the proton motive force
(PMF) Slide 20 20 The Q Cycle Slide 21 21 PMF drives ATP synthesis
Importance of PMF diffusion of protons back across membrane (down
gradient) drives formation of ATP ATP synthase enzyme that uses PMF
down gradient to catalyze ATP synthesis functions like rotary
engine with conformational changes Slide 22 22 ATP synthase
structure and function Slide 23 23 ATP Yield During Aerobic
Respiration maximum ATP yield can be calculated includes P/O ratios
of NADH and FADH 2 ATP produced by substrate level phosphorylation
the theoretical maximum total yield of ATP during aerobic
respiration is 38 the actual number closer to 30 than 38 Slide 24
24 Theoretical vs. Actual Yield of ATP amount of ATP produced
during aerobic respiration varies depending on growth conditions
and nature of ETC under anaerobic conditions, glycolysis only
yields 2 ATP molecules Factors Affecting ATP Yield bacterial ETCs
are shorter and have lower P/O ratios ATP production may vary with
environmental conditions PMF in bacteria and archaea is used for
other purposes than ATP production (flagella rotation) precursor
metabolite may be used for biosynthesis Slide 25 25 Anaerobic
Respiration uses electron carriers other than O 2 generally yields
less energy because E 0 of electron acceptor is less positive than
E 0 of O 2 Slide 26 26 An Example dissimilatory nitrate reduction
use of nitrate as terminal electron acceptor the anaerobic
reduction of nitrate makes it unavailable to cell for assimilation
( , ) or uptake denitrification reduction of nitrate to nitrogen
gas in soil, causes loss of soil fertility ETC of Paracoccus
denitrificans - anaerobic Slide 27 27 Fermentation oxidation of
NADH produced by glycolysis pyruvate or derivative used as
endogenous electron acceptor substrate only partially oxidized
oxygen not needed oxidative phosphorylation does not occur ATP
formed by substrate-level phosphorylation Slide 28 28 homolactic
fermenters heterolactic fermenters food spoilage alcoholic
fermentation alcoholic beverages, bread, etc. yogurt, sauerkraut ,
pickles , etc. Slide 29 29 Slide 30 30 Catabolism of Other
Carbohydrates many different carbohydrates can serve as energy
source carbohydrates can be supplied externally or internally (from
internal reserves) monosaccharides converted to other sugars that
enter glycolytic pathway disaccharides and polysaccharides cleaved
by hydrolases or phosphorylases Slide 31 31 Reserve Polymers used
as energy sources in absence of external nutrients e.g., glycogen
and starch cleaved by phosphorylases (glucose) n + P i (glucose)
n-1 + glucose-1-P glucose-1-P enters glycolytic pathway e.g., Poly-
-hydroxybutyrate (PHB) the soil bacterium Azotobacter PHB
acetyl-CoA acetyl-CoA enters TCA cycle Slide 32 32 Lipid Catabolism
triglycerides common energy sources hydrolyzed to glycerol and
fatty acids by lipases glycerol degraded via glycolytic pathway
fatty acids often oxidized via -oxidation pathway Slide 33 33
-oxidation pathway Slide 34 34 Protein and Amino Acid Catabolism
transfer of amino group from one amino acid to -keto acid protease
hydrolyzes protein to amino acids deamination removal of amino
group from amino acid resulting organic acids converted to
pyruvate, acetyl-CoA, or TCA cycle intermediate can be oxidized via
TCA cycle can be used for biosynthesis can occur through
transamination Slide 35 35 Chemolithotrophy carried out by
chemolithotrophs electrons released from energy source which is an
inorganic molecule transferred to terminal electron acceptor
(usually O 2 ) by ETC ATP synthesized by oxidative phosphorylation
Slide 36 36 Energy Sources bacterial and archaeal species have
specific electron donor and acceptor preferences much less energy
is available from oxidation of inorganic molecules than glucose
oxidation due to more positive redox potentials Slide 37 37 Three
Major Groups of Chemolithotrophs have ecological importance several
bacteria and archaea oxidize hydrogen sulfur-oxidizing microbes
hydrogen sulfide (H 2 S), sulfur (S 0 ), thiosulfate (S 2 O 3 2- )
nitrifying bacteria oxidize ammonia to nitrate Slide 38 38
Sulfur-oxidizing bacteria ATP can be synthesized by both oxidative
phosphorylation and substrate-level phosphorylation Slide 39 39
Nitrifying Bacteria Example requires 2 different genera oxidize
ammonia to nitrate NH 4 + NO 2 - NO 3 - Slide 40 40 Reverse
Electron Flow by Chemolithotrophs Calvin cycle requires NAD(P)H as
electron source for fixing CO 2 many energy sources used by
chemolithotrophs have E 0 more positive than NAD + (P)/NAD(P)H use
reverse electron flow to generate NAD(P)H Metabolic Flexibility of
Chemolithotrophs many switch from chemolithotrophic metabolism to
chemoorganotrophic metabolism many switch from autotrophic
metabolism (via Calvin cycle) to heterotrophic metabolism Slide 41
41 Phototrophy photosynthesis energy from light trapped and
converted to chemical energy a two part process light reactions in
which light energy is trapped and converted to chemical energy dark
reactions in which the energy produced in the light reactions is
used to reduce CO 2 and synthesize cell constituents oxygenic
photosynthesis eucaryotes and cyanobacteria anoxygenic
photosynthesis all other bacteria Slide 42 42 Phototrophic fueling
reactions Slide 43 43 photosynthetic eukaryotes and cyanobacteria
oxygen is generated and released into the environment most
important pigments are chlorophylls The Light Reaction in Oxygenic
Photosynthesis Slide 44 44 The Light Reaction in Oxygenic
Photosynthesis chlorophylls major light-absorbing pigments
accessory pigments transfer light energy to chlorophylls e.g.,
carotenoids and phycobiliproteins Different chlorophylls have
different absorption peaks Chlorophyll structure Slide 45 45
Accessory pigments absorb different wavelengths of light than
chlorophylls Slide 46 46 Organization of pigments antennas highly
organized arrays of chlorophylls and accessory pigments captured
light transferred to special reaction-center chlorophyll directly
involved in photosynthetic electron transport photosystems antenna
and its associated reaction-center chlorophyll electron flow PMF
ATP Slide 47 47 noncyclic electron flow ATP + NADPH made (noncyclic
photophos- phorylation) cyclic electron flow ATP made (cyclic
photophos- phorylation) Oxygenic Photosynthesis Slide 48 48
electron flow PMF ATP The Mechanism of Photosynthesis Slide 49 49
Purple nonsulfur bacteria, Rhodobacter sphaeroides The Light
Reaction in Anoxygenic Photosynthesis H 2 O not used as an electron
source; therefore O 2 is not produced only one photosystem involved
uses different pigments and mechanisms to generate reducing power
carried out by phototrophic green bacteria, phototrophic purple
bacteria and heliobacteria (similar to PSII) electron source for
generation of NADH by reverse electron flow Slide 50 50 Green
sulfur bacteria (similar to PSI) Photosynthetic electron transport
system of Chlorobium limicola. MK is the quinone menaquinone. Slide
51 51 Bacteriorhodopsin-Based Phototrophy Some archaea use a type
of phototrophy that involves bacteriorhodopsin, a membrane protein
which functions as a light-driven proton pump a proton motive force
is generated an electron transport chain is not involved
