Lecture 3-4
Study Guide
Pathways, Cycles, and Reactions to Review
Glycolysis – Separate sheet
Pentose Phosphate Pathway ( Reactions )
 Oxidation of glucose 6- phosphate to phosphogluconate
 Oxidation of 6-phosphogluconate to ribulose 5- phosphate and CO2
 Ribulose 5- phosphate is then converted to 3-5 sugar phosphate
Pentose Phosphate Pathway ( Functions)
 Intermediates formed – Fructose – 6 phosphate and Glyceraldehyde 3-phosphate
can be used in the glycolytic pathway
 NADPH which is formed serves as the source of electrons for molecules during
biosynthesis
 Transketolose transfers 2 C group: Transaldolase transfers 3C group
 Erythrose 4-phosphate is used to synthesize aromatic amino acids and vitamin B6
 Ribose 5- phosphate can be used for the synthesis of nucleic acids
 Ribulose 1,5- biphosphate is the primary CO2 acceptor in photosynthesis.
 Intermediates may be used to produce ATP
Summary
Glucose 6-phosphate + 12 NADP+ + 7 H2O
6CO2 + 12 NADPH + H+ + Pi
Fermentations
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Microorganisms use pyruvate or a derivative as an electron or hydrogen acceptor for
the reoxidation of NADH. This regenerates NAD+ which is needed for the gycolytic
pathway.
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General Principle – NADH + H+ is oxidized to NAD+ and the electron acceptor is
usually pyruvate or a pyruvate derivative
Types of fermentation
 Alcoholic fermentation – 2 step process. Pyruvate undergoes a decarboxylation
reaction from a 3C to a 2C compound, acetaldehyde. Acetaldehyde is then reduced
to alcohol and NADH + H+ is oxidized to NAD+.
 Lactic acid fermentation – Pyruvate is reduced to lactate( Pyruvic acid to lactic acid)
Homolactic – use the glycolytic pathway and reduce all of their pyruvate to lactate
Heterolactic – form products other than lactate – ethanol and CO2.
 Mixed acid fermentation results in the production of a mixture of acids, acetic,
lactic, succinic, and formic as well as the production of CO2.
 Formic acid fermentation – Enterobacteriaceae – Produce formic acid and convert it
to CO2 and H2 with formic hydrogenlyase
HCOOH
CO2 and H2
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Butanediol fermentation is characteristic of Enterobacter, Serratia, Erwinia, and
Proteus. Pyruvate is converted to acetoin which is then reduced to 2,3 butaanediol
with NADH. A large amount of ethanol is also produced.
Anaerobic butylic-butyric acid fermentation occurs in Clostridium species that cause
botulism and tetanus
Mannitol fermentation – Characteristic of Staphylococcus aureus
Stickland Reaction
 One amino acid is reduced and the other acts as the electron acceptor.
 Alanine is oxidized and glycine is reduced to form acetate, CO2 and NH3.
 Can form ATP
 Common to Clostridium species
 Oxidation of alanine, leucine, isoleucine, valine, phenylalanine, tryptophan, and
histidine
Tricarboxylic Acid Cycle( Citric Acid Cycle)
TCA cycle occurs in a variety of aerobic bacteria, algae, and fungi.
It is an important source of energy
E. coli which is a facultative anaerobe – uses the TCA under specific circumstances
Most microorganisms even ones that do not do the complete TCA have the enzymes
for the cycle
 In this reaction pyruvate ( 3C) is oxidized by a complex enzyme Pyruvate
dehydrogenase to Acetyl COA and CO2. ( NADH = H+ is formed)
 In the cycle Acetyl COA is added to OAA to form the 6 C compound citric acid
Which starts the cycle
 In the cycle – three NADH + H+ are formed and one FADH2/ One GTP is formed. (
page 178)
 One of the most significant aspects of the Tricarboxylic acid cycle is its function in
providing Carbon skeletons for biosynthesis through its intermediates
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Electron Transport Chain and the production of ATP
E. coli
Paracoccus denitrificans
Transports electrons from NADH to
Transfers electrons from NADH to
acceptors
acceptors and succinate – oxidizes methanol
and methylamines the carbon source
Facultative anaerobe – Aerobic or anaerobic
Facultative anaerobe, that grows
respiration
heterotrophically or autrotrphically –
aerobic respiration or anaerobic respiration
with with nitrate as the acceptor
Moves protons across the plasma membrane
Moves protons across the membrane
Cytochromes unique - branched
Cytochromes present
Ubiquinol donates electrons to both
Aerobically connects to the Calvin cycle
branches
Anaerobically connects to nitrite reductase,
nitric oxide reductase
Branches based upon conditions for growth
Is involved in denitrification
and levels of oxygen
Chemiosmosis
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The production of a proton gradient across the plasma membrane between the
periplasm and cytoplasm of bacterial cells
Produces ATP by the movement of the protons through a channel which is catalyzed
by ATP synthase. The ATPase activity is on the inner surface of the plasma
membrane in bacteria.
The movement of the protons through the channel drives oxidative phosphorylation
The final step oxygen is reduced to form water
Antibiotics can block this process.
The antibiotic piericidin competes with Coenzyme Q in the chain – competitive
inhibition
There are also molecules that stop the ATP synthesis
Catabolic Reactions
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Common disaccharides are cleaved to monosaccharides
Polysaccharides are cleaved to smaller molecules
Reserve carbohydrates like glycogen and starch may be broken down by
phsophorylases. Phosphorylases catalyze reaction win which the polysaccharide
chain is shortened by one and then yields glucose 1- phosphate( This molecule can
then enter the glycolytic pathway by glucose 6- phosphate
Lipid catabolism – fatty acids and other lipids are oxidized in the Beta ocidation
pathway. In this pathway cyclic fatty acids are degraded to acetyl COA which
feeds into the TCA or they can be used in biosynthesis
Amino acid catabolism( food spoilage) – bacteria secrete protease enzymes that
hydrolyze proteins and polypeptides to amino acids which are then transported into
the cell and catabolized. Deamination is the removal of an amino group, NH2. The
acceptor of the amino group may be an alpha keto acid acceptor which can then be
converted to pyruvate, acetyl COA or an intermediate in the TCA.
Photosynthesis – Light energy is converted to chemical energy. A two step process. The
light dependent reaction is the first reaction in which energy is trapped by pigments and
fed into electron transport chains on the surface of membranes. This precedes the Light
Independent Reaction or Calvin Cycle through which carbon skeletons are generated to form
all molecules in the cell. In the process oxygen is regenerated in our biosphere.
The Light Dependent Reaction ( Cyanobacteria )
 Light is trapped by pigments
 Light is used to produce ATP< NADH, and NADPH
 Different pigments capture different wave lengths of light
 Chlorophyll A is the primary photosynthetic pigment. Chlorophyll A absorbs light at
a wavelength of 665 nm. Chlorophyll b absorbs light at a wavelength of 645nm
 Other pigments are
Carotene
Xanthophyll
Fucoxanthin
Phycoerythrin( 550 nm)
Phycocyanin( 620 nm)
 Chlorophylls and accessory pigments are arranged in organized arrays called
antennas with the reaction center chlorophyll receiving the input of energy from all
the other molecules
 Photosystem II ( 680) and Photosystem I ( 700 nm)
 Cyclic- most primitive system – P700 – electrons become excited when the energy is
transferred from the light energy to the reaction center. The highly excited
electron enters an electron transport chain which producesATP. CYCLIC
PHOTOPHOSPHORyLATION
 Non-Cyclic – involves the interaction of both Photosystem I and II. (This differs
from Green Plant photosynthesis which is pictured in your text) P 700 is excited and
donates electrons to ferredoxin, In the non cyclic reaction, Ferrodoxin reduces
NADP+ to NADPH + H+. PHotosystem Ii is required to complete this reaction, it
donates electrons to oxidized P700 and generates ATP in the process. ( The P 680 is
excited and donates electrosn to pheophytin a) Electrons subsequently travel to
Plastoquinone and dwon the electron transport chain to P700. This is NON CYCLIC
PHOTOPHOSPHORYLATION. Water is cleaved to form O2.
 Generation of ATP occurs with the same mechanism in this process as with oxidative
phosphorylation.