METABOLIC PATHWAYS
ALLOWS CELLS TO USE METABOLITES TO THEIR FULL
POTENTIAL
METABOLISM
THE SUM OF ALL CELLULAR REACTIONS
TYPES OF METABOLIC REACTIONS
ANABOLIC VS CATABOLIC
CATABOLISM
AEROBIC VS ANAEROBIC
COUPLING AGENTS
ATP
ATP STRUCTURE
• ADENINE
• RIBOSE
• THREE PHOSPHATE GROUPS
THE IMPORTANCE OF HIGH ENERGY BONDS
• THIRD PHOSPHATE BOND
• UNSTABLE
• HYDROLYSIS IS EXERGONINC
ENERGY METABOLISM
OXIDATION VS REDUCTION
BIOLOGICAL OXIDATION
• REMOVAL OF ELECTIONS IN INORGANIC MOLECULES
• REMOVAL OF HYDROGENS IN ORGANIC MOLECULES
• DEHYDROGENASES
BIOLOGICAL REDUCTIONS
• ADDITIONS OF ELECTRONS IN INORGANIC
• ADDITIONS OF HYDROGENS IN ORGANIC
• OXIDATION AND REDUCTION MUST OCCUR SIMULTANEOUSLY
COUPLING AGENTS
COENZYMES
SUBSTRATES FOR OXIDATION
• INORGANIC COMPOUNDS (REDUCED IRON, SULFUR OR NITROGEN)
• HEXOSES (FRUCTOSE, GLUCOSE, LACTOSE)
• POLYSACCHARIDES
• PROTEINS
• FATS
GLUCOSE
• HEXOSE• MAIN SUGAR IN
VERTEBRATES• SUGAR RELEASED FROM
STARCH IN PLANTS• CONSTITUENT OF
SUCROSE • BEGINNING POINT FOR
EMBDEN MYERHOFF, ENTNER DUODOROFF, PENTOSE PHOSPHATE PATHWAYS
THE IMPORTANCE OF ELECTRON ACCEPTORS
• OXYGEN
• OTHER INORGANIC MOLECULES
• ORGANIC MOLECULES
AEROBIC RESPIRATION VS FERMENTATION
AEROBIC RESPIRATION
• NEED ELECTRON ACCEPTOR FOR OXIDATIONS TO OCCUR
• MOST USE OXYGEN
• ACCESS TO FULL ENERGY OF GLUCOSE REQUIRES OXIDATION
FERMENTATION
• MOST ORGANISMS CAN EXTRACT ENERGY BY EMBDEN MYERHOFF PATHWAY/GLYCOLYSIS
• DOES NOT REQUIRE OXYGEN• ELECTRONS ARE GIVEN BACK TO AN
ORGANIC MOLECULE THAT IS PYRUVATE OR A DERIVATIVE OF PYRUVATE
• LACTATE, ALCOHOL, ACIDS, ETC
ANAEROBIC RESPIRATION
• USES FINAL INORGANIC ELECTRON ACCEPTOR OTHER THAN ATMOSPHERIC OXYGEN
CLASSIFICATION OF ORGANISMS BY THEIR USE OF OXYGEN
• STRICT OR OBLIGATE AEROBES
• STRICT OR OBLIGATE ANAEROBES
• FACULATIVE ANAEROBES
EMBDEN - MEYERHOFF PATHWAY
GLYCOLYSIS
EMBDEN-MEYERHOFF
• TEN STEP PATHWAY
• FOUND IN BOTH AEROBIC AND ANAEROBIC ORGANSIMS
• PYRUVATE IS THE END PRODUCT
• CAN BE REDUCED THROUGH FERMENTATION
• OR OXIDIZED FURTHER
PRODUCTS OF EMBDEN MEYERHOFF
• NADH
• ATP
• PYRUVATE
PHASES OF THE EMBDEN MEYERHOFF PATHWAY
• PREPRATORY AND CLEAVAGE– STEPS 1-5
• OXIDATIVE – STEPS 6 & 7
• ATP GENERATING PHASE– STEPS 8-10
PREPARATION AND CLEAVAGE
• FRUCTOSE 1,6 BISPHOSPHATE
• TWO TERMINAL PHOSPHATE GROUPS
• DHAP AND GLYCERALDEHYDE 3 PHOSPHATE
DHAP AND GLYCERALDEHYDE 3 PHOSPHATE
• DHAP = KETOSE
• GLYCERALDEHYDE 3 PHOSPHATE = ALDOSE
• ONLY GLYCERALDEHYDE 3 PHOSPHATE OXIDIZED
OXIDATION AND ATP GENERATION
• NEGATIVE ENERGY YIELD SO FAR
• ATP PRODUCTION LINKED TO OXIDATION
• GLYCERALDEHYDE 3 DEHYDROGENASE
PYRUVATE & ATP FORMATION
• ISOMERIZATION REACTION TO INCREASE AMOUNT OF FREE ENERGY
• 3 PHOSPHOGLCERAATE TO 2PHOSPHOGLYCERATE TO PHOSPHENOLPYRUVATE
• PHOSPHOENOLPYRUVATE TO PYRUVATE
IMPORTANCE OF PYRUVATE
• BRANCHING POINT
• FATE DEPENDS ON ORGANISM AND OXYGEN
CATABOLISM OF GLUCOSE BY CELLULAR RESPIRATION
ENERGY RELEASE IS EXACTLY THE SAME AS WHEN SUGAR IS
THROWN ONTO A FIRE
BURNING GLUCOSE IN OXYGEN RELEASES 686,00
CALORIES PER MOLE
CELLS WILL NOT CAPTURE ALL THIS ENERGY
THE CATABOLISM OF GLUCOSE
• GLYCOLYSIS—EMBDEN MERYEHOFF PATHWAY
• KREBS CYCLE—TCA CYCLE
• ELECTRON TRANSPORT
STEP ONE OF GLYCOLYSIS
• SUBSTRATE PHOSPHORYLATION OF GLUCOSE
• CONVERSION TO GLUCOSE 6 PHOSPHATE
• GLUCOSE TRAPPING
• HEXOKINASE IS THE ENZYME USED IN EUKARYOTES
HORMONAL REGULATION
• MAMMALS REGULATE THIS PHOSPHORYLATION WITH THE HORMONE INSULIN
• THERE ARE MANY HORMONES THAT HELP REGULATE SUGAR METABOLISM
STEP TWO OF GLYCOLYSIS
• GLUCOSE 6 PHOSPHATE IS REARRANGED INTO FRUCTOSE 6 PHOSPHATE
• PHOSPHOFRUCTOKINASE IS THE ENZYME USED
STEP THREE OF GLYCOLYSIS
• SUBSTRATE PHOSPHORYLATION OF FRUCTOSE 6 PHOSPHATE TO FORM FRUCTOSE 1, 6 DIPHOSPHATE
• CAN ALSO BE CALLED FRUCTOSE 1,6 BISPHOSPHATE
• PHOSPHOFRUCTOKINASE IS THE ENZYME USED
IMPORTANCE OF PHOSPHOFRUCTOKINASE
• EXTENSIVELY STUDIED ENZYME
• KEY REGULATOR OF GLYCOLYTIC PATHWAY
• ACTIVITES STIMULATED BY FRUCTOSE 6 PHOSPHATE, AMP AND ADP
• ACTIVITIES INHIBITED BY ATP AND CITRATE
PHOSPHOFRUCTOKINASE ALLOWS THE CELL TO
BALANCE THE RATES OF GLYCOLYSIS AND THE
KREBS CYCLE
STEP FOUR OF GLYCOLYSIS
STEP FIVE OF GLYCOLYSIS
NO ENERGY HAS BEEN PRODUCED
• IN FACT WE HAVE INVESTED TWO ATPs
STEP SIX OF GLYCOLYSIS
STEP SEVEN OF GLYCOLYSIS
STEP EIGHT OF GLYCOLYSIS
• THIS PRIMES THE GLUCOSE FOR ATP PRODUCTION
STEP NINE OF GLYCOLYSIS
STEP TEN OF GLYCOLYSIS
FOUR ATP MOLECULES WILL BE HARVESTED IN THIS PORTION OF
THE PATHWAY
• TWO ATPs INVESTED EARLIER MUST BE PAID BACK
• THE NET YIELD OF GLYCOLYSIS IS 2 ATPs
• TWO NADHs
AEROBIC PATHWAYS
• TCA CYCLE/KREBS CYCLE
• ELECTRON TRANSPORT SYSTEM– PRODUCE CARBON DIOXIDE
• WATER
• ENERGY– STORED AS ATP
KREBS CYCLE
TCA CYCLE
PREPRATORY RX
CITRIC ACID AS A REGULATOR OF PHOSPHOFRUCTOKINASE
ACTIVITY
• CITRIC ACID IS AN INHIBITOR OF PHOSPHOFRUCTOKINASE
• PREVENTS GLYCOLYSIS FROM OCCURRING WHEN IT IS NOT NECESSARY
CITRATE IS A TERTIARY ALCOHOL
• MUST BE CONVERTED TO A SECONDARY ALCOHOL
ELECTRON TRANSPORT SYSTEM
• GLYCOLYSIS = 2 ATPs
• TCA = 2 ATPs
• MOST OF ATPs PRODUCED BY ETS
• SERIES OF ELECTRON CARRIERS
• REDOX REACTIONS
ELECTRON TRANSPORT SYSTEM
• FROM MORE NEGATIVE REDUCTION POTENTIALS TO MORE POSITIVE POTENTIALS
• DIFFERENCE BETWEEN NADH AND OXYGEN IS ABOUT 1.14 VOLTS
SITES OF ATP SYNTHESIS
• BETWEEN NADH AND COENZYME Q
• BETWEEN CYTOCHROME B AND C1
• BETWEEN CYTOCHROME A AND OXYGEN
ELECTRON TRANSPORT SYSTEM
• ALLOWS SMALL RELEASES OF ENERGY IN SMALL STEPS
• ESTABLISHES PROTON AND ELECTRICAL GRADIENT
• FOUND IN INNER MITOCHONDRIAL MEMBRANE• FOUR COMPLEXES OF CARRIERS• CYTOCHROME C AND COENZYME Q CONNECT
COMPLEXES
OXIDATIVE PHOSPHORYLATION
• AS MANY AS THREE ATPs FOR EACH TWO ELECTRONS FROM NADH TO OXYGEN
• AS MANY AS TWO ATPs FOR EACH TWO ELECTRONS FROM FADH2 TO OXYGEN
BACTERIAL ELECTRON TRANSPORT SYSTEMS
• SOME RESEMBLE MITOCHONDRIAL CHAINS
• MANY ARE VERY DIFFERENT
• VARIOUS TYPES OF CYTOCHROMES
• SOME HIGHLY BRANCHED
• MAY BE SHORTER
• HAVE LESS ATP PRODUCTION
OXIDATIVE PHOSPHORYLATION
• CHEMIOSMOSIS
• CONFORMATIONAL CHANGE HYPOTHESIS
CHEMIOSMOSIS
• PROTONS MOVE INTO INTERMEMBRANAL SPACE
• CAUSES PROTON MOTIVE FORCE• GRADIENT OF PROTONS• MEMBRANE POTENTIAL DUE TO
UNEVEN DISTRIBUTION OF CHARGES• ATPs MADE AS H+ DIFFUSE BACK
INTO MATRIX
OTHER USES OF PROTON MOTIVE FORCE
• TRANSPORT ACROSS MEMBRANES
• ROTATION OF BACTERIAL FLAGELLA
CONFORMATIONAL CHANGE HYPOTHESIS
• ENERGY RELEASED CAUSES CHANGES IN THE SHAPE OF ATPase ENZYME
• CHANGES DO ACTUALLY OCCUR DURING ELECTRON TRANSPORT
INHIBITORS OF ELECTRON TRANSPORT
• BLOCK ELECTRON TRANSPORT
• UNCOUPLE ATPase AND ELECTRON TRANSPORT
BLOCKERS
• PERICIDIN -- COMPETES WITH COENZYME Q FOR ELECTRONS
• ANTIMYCIN A -- BLOCKS ELECTRON TRANSPORT BETWEEN B AND C
• CYANIDE & AZIDE -- STOP TRANSFER BETWEEN CYTOCHROME A AND OXYGEN
UNCOUPLERS
• DO NOT AFFECT ELECTRON TRANSPORT
• DISCONNECT OXIDATIVE PHOSPHORYLATION FROM ELECTRON TRANSPORT
• ENERGY IS RELEASED AS HEAT
• DINTITOPHENOL & VALINOMYCIN
ATP YIELDS
GLYCOLYSIS & AEROBIC RESPIRATION
GLYCOLYSIS
• NET YIELD OF 2 ATPs
• TWO NADHs PRODUCE SIX ATPs
• TOTAL OF EIGHT ATPs
PREPARATORY REACTION
• 2 NADHs FOR A YIELD OF 6 ATPs
TCA CYCLE
• 2 ATPs
• 6 NADHs FOR 18 ATPs
• 2 FADH2s FOR 4 ATPs
ANAEROBIC PATHWAYS
LACTATE FERMENTATION
• DIRECT TRANSFER FROM NADH TO PYRUVATE
• LACTATE DEHYDROGENASE
• MAJOR PATHWAY IN MANY ANAEROBIC BACTERIA
• MUSCLES
ETHANOL FERMENTATION
• NADH AND ACETALDEHYDE (A DERIVATIVE OF PYRUVATE)
• TWO STEP SEQUENCE• DECARBOXYLATION--
PYRUVATE DECARBOXYLASE
• ACETALDEHYDE REDUCTION -- ALCOHOL DEHYDROGENASE
TYPES OF FERMENTATIONS
ALCOHOLIC FERMENTATION
• FUNGI
• ALGAE
• BACTERIA
• PROTOZOA
• SUGARS --------> ALCOHOL
• ALCOHOL DEHYDROGENASE
• NADH DONOR
LACTIC ACID FERMENTATION
• REDUCTION OF PYRUVATE TO LACTATE• MORE COMMON THAN ALCOHOL
FERMENTATION• BACTERIA• ALGAE• WATER MOLDS• PROTOZOA• ANIMAL MUSCLE CELLS
HOMOLACTIC ACID FERMENTERS
• LACTATE DEHYDROGENASE
• USE GLYCOLYTIC PATHWAY
• TWO KINDS OF LACTIC ACID FERMENTERS
HETEROLACTIC FERMENTERS
• MANY PRODUCE LACTATE
• ETHANOL
• VARIETY OF OTHER PRODUCTS
• USES PHOSPHOKETALOSE PATHWAY
FORMIC ACID FERMENTERS
MIXED ACID FERMENTATION
BUTANEDIOL FERMENTATION
MIXED ACID FERMENTATION
• ENTEROBACTERIACEAE
• PYRUVATE ---->
• HYDROGEN GAS
• CARBON DIOXIDE
• FORMIC HYDROGENLYASE
MIXED ACID FERMENTATION
• ETHANOL
• COMPLEX MIXTURE OF ACIDS
• ACETIC
• LACTIC
• SUCCINIC
• FORMIC
• ESCHERICHIA, SALMONELLA & ETC
ATP GENERATION IN FORMIC ACID
FERMENTATION• SOMETIME GENERATE ATP WILL
REOXIDIZING NADH
• USE ACETYL CO A -------> ACETYL-PHOSPHATE
• DONATES TO ADP
FERMENTERS OF AMINO ACIDS
• STICKLAND REACTION
• CLOSTRIDIUM SPECIES
• GENERATE AMMONIA, HYDROGEN SULFIDE, FATTY ACIDS AND AMINES
• PUTREFACTION ODORS
ANAEROBIC RESPIRATION
ANAEROBIC RESPIRATION
• ELECTRON TRANSPORT SYSTEMS DONATE ELECTRONS TO INORGANIC MOLECULES OTHER THAN OXYGEN
• NITRATE
• SULFATE
• CARBON DIOXIDE
NITRATE
• NO3 + 2 e- + 2 H+ -------> NO2 + H2O
• NITRATE IS THE ELECTRON ACCEPTOR
• NITRATE REDUCTASE REPLACES CYTOCHROME OXIDASE
• NOT EFFECTIVE
• PRODUCT TOXIC
DENITRIFICATION
• REDUCED ALL THE WAY TO N2
• ACCEPTS FIVE ELECTRONS
• IS NONTOXIC
• 2 NO3 + 10 e- + 12 H+ ------> N2 + 6 H2O
THE PENTOSE-PHOSPHATE PATHWAY
THE PENTOSE PHOSPHATE PATHWAY
• HEXOSE MONOPHOSPHATE PATHWAY
• CAN OPERATE AT SAME TIME AS EMBDEN-MEYERHOF
• AEROBIC OR ANAEROBIC• PROVIDES THREE TO SEVEN
CARBON SUGARS PHOSPHATE• NADPH IS ALSO PRODUCED
END PRODUCTS
• FRUCTOSE 6 PHOSPHATE
• GLYCERALDEHYDE 3 PHOSPHATE
• THREE CARBON DIOXIDE MOLECULES
• 6 NADPHs
• INTERMEDIATES FOR ANABOLIC REACTIONS
P GLUCOSE 6 - PHOSPHATE
`
NADPH
6-PHOSPHOGLUCONATE
NADPH
RIBULOSE 5 - PHOSPHATE
END PRODUCTS
ERYTHROSE 4 PHOSPHATE XYLOSE 5 PHOSPHATE
GLYCERALDEHYDE 3 PHOSPHATE FRUCTOSE 6 PHOSPHATE
IMPORTANCE OF PENTOSE PHOSPHATE PATHWAY
• MAKES ATP• NADPH ACTS AS SOURCE OF
ELECTRONS FOR BIOSYNTHESIS• PRODUCES FOUR AND FIVE CARBON
SUGARS WHICH CAN BE USED • PRODUCES HEXOSE SUGARS FOR
MICROBES GROWN ON PENTOSE CARBON SOURCE
ENTNER DOUDOROFF PATHWAY
• STARTS WITH GLUCOSE 6 PHOSPHATE
• DEHYDRATION FORMS KDPG
• END PRODUCTS ARE PGAL AND PYRUVATE
• PGAL CAN ENTER LOWER PART OF GLYCOLYSIS
• ONE ATP, ONE NADPH AND ONE NAD
BETA OXIDATION
BETA OXIDATION
• REMOVAL OF TWO CARBON GROUPS
• TO FORM ACETYL CoA– MAY ENTER KREBS CYCLE
• NADH AND FADH2 IS FORMED
PROTEIN METABOLISM
AMINO ACID BIOSYNTHESIS
• ADD AMINE GROUP TO KETO ACID
• SIMPLE ONE STEP TRANSMINATION REACTION– GLUTAMATE AND ASPARTATE ARE
EXAMPLES
CATABOLISM OF AMINO ACIDS
• REMOVAL OF AMINE GROUP FROM AMINO ACID
•
CATABOLISM OF PROTEINS AND AMINO ACIDS
• PATHOGENIC, FOOD SPOILERS, SOIL MICROBES
• PROTEASE ENZYMES• DEAMINATION• TRANSAMINATION• ALPHA KETO ACID ACCEPTOR• AMMONIUM ION MAY MAKE
MEDIUM ALKALINE