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Chapter 5 – Microbial Metabolism
Catabolic and Anabolic Reactions
• Metabolism – __________________________________
• Recall from Module 1:
o Energy can be _______ when covalent bonds _______
o Energy can be _______ when covalent bonds _______
• Catabolism –
o
o
o
o Generally _________ reactions
o Purpose is to __________________________
§ ______ ATP
• Anabolism –
o
o
o
o Generally _______________ reactions
o Purpose is to
§ _____ ATP
• Catabolism provides _______________________ and _____________ for anabolism
o Catabolic reactions are “coupled with” anabolic reactions
o _________________ is transferred from one reaction to another
• Reactions are coupled by “_____”
o _____ is formed from catabolic reactions
o _____ is used by anabolic reactions
• A metabolic pathway
o A _________ of chemical _____________ in a cell
• All metabolic reactions are carried out by a group of proteins – ________
Enzymes
Enzymes and chemical reactions
• Enzymes are biological catalysts
o
o
o
Enzyme specificity
• Enzymes act on one or more “________________”
o ________ bind at __________
• Each enzyme is specific
o
o
• Specificity is due to _____________ of enzyme
o Recall, proteins (enzymes) have characteristic ________
o _______ is essential for _______
Naming enzymes
• Names of enzymes end in “–ase”
o Sucrase, catalase, DNA polymerase
• 6 general classes of enzymes
o Grouped according to general type of reaction catalyzed
o Enzymes are named for specific reaction they catalyze
Enzyme components
• Many enzymes are made entirely of _________________
• Some consist of 2 components
o Apoprotein –
o Cofactor § Can be _______________; iron, zinc, magnesium
§ Can be organic; called a “_________________”
• Holoenzyme –
o
The mechanism of enzymatic action
• The general sequence of events in an enzymatic reaction:
o Substrate(s) binds to ________________
§ This is called ______________________
o The substrate(s) is transformed
o Transformed molecule(s), the ______________, are released from enzyme
§ No longer ____________________
§ Enzymes only ___________ to _____________
o Enzyme is free to ___________________________________
Factors influencing enzymatic activity
• Various factors and conditions affect enzyme activity
• Temperature
o In general, chemical reactions speed up as temp ________________
o For enzymes, too ______ temperature causes ________
§
o Reversible in some cases
§
• pH
o pH is
o Too much or too little
• Inhibitors
o Certain chemicals that bind to enzymes
§
o Two classes of inhibitors:
§ Competitive inhibitors
•
• Shaped like substrate (can bind), but doesn’t undergo reaction
• Sulfanilamide inhibits bacterial growth
§ Noncompetitive inhibitor
•
• Also called
•
•
Binding causes change in shape of enzyme
Fluoride used to kill bacteria in mouth
Feedback inhibition
• Control of enzymatic activity by use of
o
• Anabolic reactions usually involve several steps to create a product
o A reaction “pathway”
o Similar to assembly line
o The final product often allosterically inhibits the first enzyme in series
o Prevents build up of too much product – waste of resources
Energy Production
• Energy is stored in _______________
o Recall, covalent bonds are formed by sharing electrons
• Energy is stored in ___________________ covalent bonds
o Catabolism involves stripping “high energy” __________ from molecules and
concentrate them in the bonds of ATP
Oxidation-Reduction reactions
• Oxidation –
o Often produces energy
o Loss of _________ often involve loss of ________
o ______________ – loss of hydrogen
• Reduction –
• Oxidation and reduction reactions are always coupled
o If one molecule is oxidized, another is reduced
• Paired reactions called “_________” reactions
• Catabolism is the oxidation of highly reduced molecules
The Generation of ATP
• Energy released by redox reactions “trapped” by ATP
o Formed by adding a phosphate group, P, to ADP
o Requires energy
• ATP formation can occur in three ways:
• Substrate-level phosphorylation
o Transfer of P _________________________________________________ to ADP
o Phosphorylated molecule acquired energy from
• Oxidative phosphorylation
o Electrons transferred from _____________________ to ______________ in cytosol
o Electrons are passed on to ___________________________, ETC
§ ETC consists of
o
• Photophosphorylation
o Occurs only in photosynthetic cells
o
§
o
Metabolic pathways of energy production
• Catabolism involves series of controlled reactions
o Releasing energy in one reaction generates too much heat
o Energy cannot be harnessed efficiently
o Will damage cell
• Catabolism is a series of ____________ reactions
o Electrons extracted to generate ATP
o Sequence of reactions called a pathway
• Every reaction in a pathway is performed by ___________
• Final product produced is the “__________”
o Non-final products formed are called _______________
o Secondary products produced along the way are called “______________” or
“________________”
Carbohydrate catabolism
• Carbohydrates are primary source of energy
o Glucose is most common energy source
• Glucose is broken down via two general processes:
o Cellular respiration
o Fermentation
• Both start with glycolysis – ______________
o Continue with different pathways
Glycolysis
• Glycolysis – __________ of glucose molecule (6 Carbons) to 2 pyruvic acid molecules (3 C)
o Aka “Embden-Meyerhof pathway”
• The first step in carbohydrate metabolism
• Occurs in almost all living cells
• During glycolysis:
o NAD+ is reduced to NADH – an electron carrier
o Requires 2 ATP molecules to “get started”
o Produces 4 ATP molecules
o Net production of:
§ ___ ATP molecules
§ ___ pyruvic acid molecules
§ ___ NADH molecules
• Does not require oxygen
Alternatives to glycolysis
• Many bacteria have other pathways in addition to glycolysis
• Pentose-phosphate pathway
o Operates ____________ with glycolysis
o Breaks down 5 carbon sugars (pentoses), and glucose
o Provides important by-products for synthesizing:
§
§
•
§
o Yields only ____ ATP per sugar
Entner-Doudoroff pathway
o Works _________ glycolysis
o Can metabolize glucose without glycolysis, pentose-phosphate
o Produces 1 molecule of ATP, 2 molecules of NADPH (from NADP+)
o Found in some Gram-negative bacteria
§ Usually not found in Gram-positive bacteria
Cellular respiration
• Breakdown of pyruvic acid to
• ATP generated by oxidizing glucose (remove electrons from organic molecule)
o Electrons passed to ________, found only in organisms that respire
o Electrons end up on inorganic molecule, final electron acceptor
• Two types of respiration:
o Aerobic respiration
§ Uses ________ as final electron acceptor
o Anaerobic respiration
§ Does not use ___________ as final electron acceptor
Aerobic respiration
• The Krebs cycle
o Aka ________________________ or citric acid cycle
§ A series of 8 reaction steps
§ Completely catabolizes pyruvic acid to _______________
•
§ Final end-product is same as starting reactant; a cycle
o After glycolysis, pyruvic acid (3C) is converted to acetyl-CoA (2C)
§ The “_______________ Step”
§ One _____ is lost as _____
§ ____ NADH is produced, _____ per glucose
o Acetyl-CoA “enters” Krebs cycle
§ Electrons transferred from acetyl-CoA to electron carriers
§ Main products are ________________ (similar to _______)
• Most important by-products
§ ____ ATP per acetyl-CoA by substrate-level phosphorylation
• The electron transport chain
o A sequence of __________________________________
o _____________________ created by glycolysis, Krebs cycle pass electrons to ETC
§ Become _______________
§ Return to glycolysis, Krebs cycle
o Energy from electrons drives ______ from inside cell to outside
§ Creates concentration gradient – _______________
§ High concentration of H+ outside, relative to inside of cell
§ H+ gradient favors diffusion back into cell
§ H+ cannot diffuse across membrane. Why?
§ Electrons end up on ____________________________
o H+ re-enters cell via facilitated diffusion
§ Transporter in membrane, ___________________
§ Captures potential energy in chemiosmotic gradient
§ Forms ATP
o Electrons are passed through ETC and placed on final electron acceptor
§ ____________for aerobic respiration
§ Converted to _____________
§ Organism an _____________
o In eukaryotic cells, ETC is located at inner mitochondrial membrane
Anaerobic respiration
• Similar to aerobic respiration
• Final electron acceptor is an inorganic molecule other than oxygen
o Include ________ ion (NO3-), _________ ion (SO42-), ____________ ion (CO32-)
o Amount of energy generated depends on final electron acceptor used
• Generates _______ energy than aerobic respiration
o Only part of Krebs cycle, ETC operates under anaerobic conditions
o Anaerobes grow _________________ than aerobes
Lipid and Protein Catabolism
• Other energy sources can be used
o Can oxidize ______________ and ________________
• Large polymers broken down first
o Fats are broken down by lipases
o Proteins are broken down by proteases, peptidases
• Smaller subunits enter catabolism at various points of _______________________________
Fermentation
• Conversion of pyruvic acid into __________________ end-product
o Main purpose to
o _______________________ can participate in glycolysis again
o Produces only small amounts of ATP
• Defined as:
o
o
o
o
• ATP is only generated by glycolysis
• End-products vary on the microorganism, many fermentations exist
o Lactic acid fermentation
§ Molecules of ___________ used to convert ________________________
§ Lactic acid bacteria include Streptococcus and Lactobacillus
§ Important in food industry
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o Alcohol Fermentation
§ Pyruvic acid converted to _________________
§ Regenerates NAD+
§ Performed by number of bacteria and yeast
§ The yeast Saccharomyces cerevisiae important in food industry
Photosynthesis
• Synthesis of _________________ from ______________________
o ___________ from ______________________
o Requires ___________________
• First, conversion of _____________________ into _______________________
• Second, _________________ used to drive conversion of ___________________________
• Making organic carbon from CO2 is called “_________________” or “________________”
• Proceeds in two steps: light dependent (light) reactions and light independent (dark) reactions
o The light reactions: Photophosphorylation
§ Light energy is absorbed by ______________
• In ________________ of _______________ in green algae, plants
• In __________________ of cyanobacteria
• Other bacteria use bacteriochlorophylls
• Light “___________” or energizes electrons in ______________
§ Excited electrons are passed to _____________
• ATP is generated
§ Cyclic photophosphorylation
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•
§
Noncyclic photophosphorylation
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• Electron are placed on _______________, forms _______________
• Produces ___________, ___________ as waste
o The dark reactions: The Calvin-Benson cycle
§ No __________ is required for them to occur
§ Uses ATP, NADPH to “________” carbon dioxide
• Makes __________
Metabolic diversity among organisms
• Organisms classified according to ______________
o
• Specifically, look at basic requirements to sustain life
o
• Two energy sources
o Phototrophs –
o Chemotrophs –
Two carbon sources
o Autotrophs (self-feeders) –
§ Aka ____________________________
o Heterotrophs (feeders on others) –
§ Aka _______________________________
Classification can be combined
• Photoautotroph
o
o Include photosynthetic bacteria (green and purple bacteria, cyanobacteria), algae,
plants
o Cyanobacteria, algae, plants produce oxygen – “oxygenic” photosynthesis
o The green and purple sulfur bacteria don’t produce oxygen – “anoxygenic”
photosynthesis
• Photoheterotroph
o
o Can’t convert carbon dioxide to sugar
o Anoxygenic photosynthesis
o Include green nonsulfur (Chloroflexus) and purple nonsulfur bacteria
(Rhodopseudomonas)
• Chemoautotrophs
o
o Inorganic sources of energy:
§ Hydrogen sulfide, elemental sulfur, ammonia, nitrite ions, hydrogen gas,
ferrous iron, carbon monoxide
o ATP produced by oxidative phosphorylation
• Chemoheterotrophs
o
o Energy source and carbon source usually the same
§ Eg, glucose used for energy and carbon
• Electrons in glucose used for energy
• Carbons in glucose used for carbon
o Heterotrophs classified according to their source of organic molecule
§ Saprophytes –
§ Parasites –
o Metabolic diversity of great interest
§ Can cause problems, provide potential solutions
• Rubber degrading bacteria can destroy gaskets in machinery
• BUT, can be used to degrade discarded tires
• Rhodococcus erythropolis can cause disease in humans, animals
• BUT, can remove sulfur from petroleum
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