Microbial MetabolismMicrobial MetabolismCh. 8- pg 216Ch. 8- pg 216

Metabolism- Greek- to changeMetabolism- Greek- to change

EnzymesEnzymes

What is metabolism?What is metabolism?

The sum of chemical The sum of chemical reactions within a reactions within a living organismliving organism C6H12O6 + 6O2

6CO2 + 6H2O + energyH2O

O 2

ATP

NA

DH

NAD+

H+

e-

Why do we need to know about Why do we need to know about microbial metabolism?microbial metabolism?

Metabolism is the basis of all life, not just Metabolism is the basis of all life, not just microbesmicrobes

Metabolism forms the basis of all forms of Metabolism forms the basis of all forms of microbiology from environmental microbiology microbiology from environmental microbiology to medical microbiologyto medical microbiology

If your interest is in human health, knowledge If your interest is in human health, knowledge of metabolism forms the basis of antibiotic of metabolism forms the basis of antibiotic therapy. Some antibiotics interfere with therapy. Some antibiotics interfere with metabolic reactionsmetabolic reactions

Catabolic and Anabolic reactionsCatabolic and Anabolic reactions

CatabolismCatabolism degradative; breaks the bonds of larger molecules forming degradative; breaks the bonds of larger molecules forming

smaller molecules; releases energy smaller molecules; releases energy Generally hydrolytic- absorbs water Generally hydrolytic- absorbs water exergonic (produce energy)-energy stored in chemical bonds exergonic (produce energy)-energy stored in chemical bonds

is releasedis released AnabolismAnabolism

biosynthesis; process that forms larger macromolecules from biosynthesis; process that forms larger macromolecules from smaller molecules; requires energy input smaller molecules; requires energy input

Generally dehydration synthesis reactions (release water)Generally dehydration synthesis reactions (release water) Endergonic (consume energy) Endergonic (consume energy)

Enzymes-the driving force of Enzymes-the driving force of metabolic reactions metabolic reactions

An enzyme is a biological catalyst that speeds An enzyme is a biological catalyst that speeds up chemical reactions is the cell up chemical reactions is the cell

Increase the rate of a chemical reaction 10Increase the rate of a chemical reaction 1088-10-101010 times – to the speed of lifetimes – to the speed of life

Specific for a particular substrate and reactionSpecific for a particular substrate and reaction The unique three-dimensional shape of an The unique three-dimensional shape of an

enzyme allows it to recognize its substrateenzyme allows it to recognize its substrate

How do enzymes work?How do enzymes work? Decrease the activation Decrease the activation

energy, the energy energy, the energy required to initiate a required to initiate a chemical reactionchemical reaction

Enzymes have an active Enzymes have an active site at which only specific site at which only specific reactants or substrates reactants or substrates are positioned for various are positioned for various interactions.interactions.

Pg 219-textPg 219-text

Enzyme-substrate interactionEnzyme-substrate interaction

Active site

Turnover numberTurnover number Enzymes participate in chemical reactions but are not Enzymes participate in chemical reactions but are not

consumed by them (can function over and over again)consumed by them (can function over and over again) An enzymes speed or turnover number is the An enzymes speed or turnover number is the

maximum number of substrate molecules an enzyme maximum number of substrate molecules an enzyme molecule can convert to product each secondmolecule can convert to product each second

Enzyme speeds can range over several orders of Enzyme speeds can range over several orders of magnitude but are characteristic of a particular enzymemagnitude but are characteristic of a particular enzyme

ExamplesExamples DNA polymerase (DNA synthesis) 15DNA polymerase (DNA synthesis) 15 Catalase (breakdown of HCatalase (breakdown of H22OO22) 20,000 ) 20,000

Enzyme componentsEnzyme components Simple enzymes- consist entirely of proteinSimple enzymes- consist entirely of protein Conjugated enzymes (Conjugated enzymes (HoloenzymeHoloenzyme )consist of: )consist of:

ApoenzymeApoenzyme-the protein component-the protein component CofactorCofactor-non protein component -non protein component

metallic cofactors – iron, copper, magnesium, calcium metallic cofactors – iron, copper, magnesium, calcium vitamins , organic molecules (vitamins , organic molecules (coenzyme)coenzyme)

Apoenzyme + cofactor = Apoenzyme + cofactor = HoloenzymeHoloenzyme In the absence of the cofactor, the apoenzyme is inactiveIn the absence of the cofactor, the apoenzyme is inactive

CoenzymesCoenzymes Can act in catalysis by accepting a Can act in catalysis by accepting a

chemical group from one substrate chemical group from one substrate and transferring it to another and transferring it to another substrate substrate

Some act as electron carriersSome act as electron carriers Many are derived from vitamins. Many are derived from vitamins.

Examples: Examples: vitamin Bvitamin B66-coenzyme in amino -coenzyme in amino

acid metabolism, acid metabolism, Folic acid-coenzyme in the Folic acid-coenzyme in the

synthesis of nucleotidessynthesis of nucleotides

Important coenzymes in cellular Important coenzymes in cellular metabolismmetabolism

Nicotinamide adenine dinucleotide (NADNicotinamide adenine dinucleotide (NAD++) ) NADNAD++ is involved in catabolic reactions is involved in catabolic reactions

Nicotinamide adenine dinucleotide phosphate Nicotinamide adenine dinucleotide phosphate (NADP(NADP++)) NADPNADP++ is involved in anabolic reactions is involved in anabolic reactions

Both NAD+ and NADPH are derivatives of vitamin Both NAD+ and NADPH are derivatives of vitamin BB11 (niacin) and they both function as electron (niacin) and they both function as electron

carrierscarriers

Other key coenzymesOther key coenzymes The flavin coenzymesThe flavin coenzymes

Flavin mononucleotide (FMN) and flavin adenine Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)dinucleotide (FAD)

Derivatives of vitamin BDerivatives of vitamin B22 (riboflavin) (riboflavin) Also act as electron carriersAlso act as electron carriers

Coenzyme ACoenzyme A Derivative of vitamin BDerivative of vitamin B55 (pantothenic acid) (pantothenic acid) Important roles in fat metabolism and the TCA Important roles in fat metabolism and the TCA

(Tricarboxylic Acid) cycle(Tricarboxylic Acid) cycle

Naming enzymes-Naming enzymes-substrate acted on or type of reactionsubstrate acted on or type of reaction

Class (-”-ase”)Class (-”-ase”) Type of chemical reactionType of chemical reaction

OxidoreductaseOxidoreductase Oxidation-reduction (redox) reactions. Loss or gain Oxidation-reduction (redox) reactions. Loss or gain of electrons. of electrons.

TransferaseTransferase Transfer of functional groups, such as an amino or Transfer of functional groups, such as an amino or a phosphate groupa phosphate group

HydrolaseHydrolase Cleaves bonds on molecules with the addition of Cleaves bonds on molecules with the addition of water (hydrolysis)water (hydrolysis)

LyaseLyase Removal or addition of groups of atoms without Removal or addition of groups of atoms without hydrolysishydrolysis

IsomeraseIsomerase Rearrangement of atoms within a moleculeRearrangement of atoms within a molecule

LigaseLigase Joining two molecules (using energy from the Joining two molecules (using energy from the breakdown of ATP)breakdown of ATP)

See pg 224- Microbits 8.3- The enzyme Name GameSee pg 224- Microbits 8.3- The enzyme Name Game

Oxidation-Reduction ReactionsOxidation-Reduction Reactions

Oxidation- loss or removal of electronsOxidation- loss or removal of electrons Many substances combine with oxygen and transfer elections Many substances combine with oxygen and transfer elections

to oxygen. Substance becomes oxidizedto oxygen. Substance becomes oxidized If another electron receptor is present, oxygen does not need If another electron receptor is present, oxygen does not need

to be present.to be present. Reduction- gain of electronsReduction- gain of electrons

Substance becomes reduced.Substance becomes reduced. Because oxidation and reduction must occur Because oxidation and reduction must occur

simultaneously, reactions of called redox reactions.simultaneously, reactions of called redox reactions.

Comparison of oxidation and Comparison of oxidation and ReductionReduction

OxidationOxidation Loss of electronsLoss of electrons Gain of oxygenGain of oxygen Loss of hydrogenLoss of hydrogen Loss of energry-liberates Loss of energry-liberates

energyenergy Exothermic, exergonicExothermic, exergonic

Gives off heatGives off heat

ReductionReduction Gain of electronsGain of electrons Loss of oxygenLoss of oxygen Gain of hydrogenGain of hydrogen Gain of energy- energy Gain of energy- energy

stored in reduced stored in reduced compoundcompound

Endothermic; endergonicEndothermic; endergonic Requires energy, such as Requires energy, such as

heat.heat.

Factors affecting enzymatic activityFactors affecting enzymatic activity

-rate of chemical reactions increases with temperature

-elevation above a certain temperature reduces enzymatic activity due to denaturation of the enzyme

-most enzymes have a pH optimum

-changes in pH can cause result in alterations in the 3D-structure of the enzyme leading to denaturation

-high substrate concentration leads to maximal enzyme activity, the enzyme is said to be saturated

-under normal conditions enzymes are not saturated

Exo and endoenzymesExo and endoenzymesExoenzymesExoenzymes Active outside Active outside

the cellthe cell Breakdown of Breakdown of

nutrients that are nutrients that are too large to enter too large to enter the cell. the cell.

Some play a role Some play a role in disease e.g., in disease e.g., Streptokinase; Streptokinase; phospholipase Cphospholipase C

EndoenzymesEndoenzymes Most metabolic Most metabolic

enzymes are enzymes are endoenzymesendoenzymes

Control of metabolic pathwaysControl of metabolic pathways

Metabolic pathways are Metabolic pathways are controlled at the level of controlled at the level of their enzymestheir enzymes

Control of enzymesControl of enzymes SynthesisSynthesis ActivityActivity

Production of enzymes in the cellProduction of enzymes in the cell

Enzymes can be produced at constant levels in the cell (constitutive enzymes) OR

Their production can be regulated in response to substrate( induced enzymes) or product concentrations (feedback mechanisms).

Constitutive enzymesConstitutive enzymes – always present, – always present, always produced in equal amounts or at always produced in equal amounts or at equal rates, regardless of amount of equal rates, regardless of amount of substratesubstrate enzymes involved in glucose metabolismenzymes involved in glucose metabolism

Regulated enzymesRegulated enzymes – not constantly – not constantly present; production is turned on (induced) or present; production is turned on (induced) or turned off (repressed) in response to changes turned off (repressed) in response to changes in concentration of the substratein concentration of the substrate

Enzyme InhibitorsEnzyme Inhibitors An effective way to control the growth of An effective way to control the growth of

bacteria is to control their enzymesbacteria is to control their enzymes Certain poisons such as cyanide, arsenic and Certain poisons such as cyanide, arsenic and

mercury combine with enzymes and inhibit their mercury combine with enzymes and inhibit their activityactivity

Enzyme inhibitors can be classed asEnzyme inhibitors can be classed as Competitive inhibitorsCompetitive inhibitors Noncompetitive inhibitorsNoncompetitive inhibitors

Competitive inhibitorsCompetitive inhibitors Fill the active site and compete Fill the active site and compete

with substratewith substrate Similar in shape and chemical Similar in shape and chemical

structure to the substratestructure to the substrate Does not undergo any reaction to Does not undergo any reaction to

form productsform products May bind reversibly or irreversibly. May bind reversibly or irreversibly.

e.g., Inhibition of folic acid e.g., Inhibition of folic acid synthesis by sulfanilamide synthesis by sulfanilamide

Noncompetitive inhibitorsNoncompetitive inhibitors Interact with a site other Interact with a site other

than the active site than the active site (allosteric or regulatory site)(allosteric or regulatory site)

Binding of the inhibitor Binding of the inhibitor causes a change in the causes a change in the shape of the active site, shape of the active site, making it nonfunctional making it nonfunctional (allosteric inhibition)(allosteric inhibition)

May bind reversibly or May bind reversibly or irreversiblyirreversibly

Enzyme RepressionEnzyme Repression The end-product of the reaction signals back to The end-product of the reaction signals back to

the DNA to turn off expression of the genethe DNA to turn off expression of the gene

Prevents the cell from wasting energyPrevents the cell from wasting energy

The Cell’s Energy MachineThe Cell’s Energy Machine