ch. 7 (microbial metabolism)

Microbial Metabolism

Chapter 7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Learning Outcomes: Section 7.1

1. Describe the relationship among metabolism, catabolism, and anabolism.

2. Fully define the structure and function of enzymes.

3. Differentiate between constitutive and regulated enzymes.

4. Diagram some different patterns of metabolism.

5. Describe how enzymes are controlled.

Metabolism and the Role of Enzymes

•Metabolism: pertains to all chemical reactions and physical workings of the cell

•Anabolism: -a building and bond-making process that forms

larger macromolecules from smaller ones

-requires the input of energy (ATP)

•Catabolism:-breaks the bonds of larger molecules into smaller

molecules

-releases energy (used to form ATP)

Simplified Model of MetabolismCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Rel

ati

ve

co

mp

lex

ity

of

mo

lec

ule

s

ANABOLISM

ANABOLISM

ANABOLISM

Nutrientsfrom outsideor frominternalpathways

Glycolysis

Krebs cycle

Respiratorychain

Fermentation

Yields energy Uses energy Uses energy Uses energy

Some assemblyreactions occurspontaneously

Complex lipids

RNA + DNA

Peptidoglycan

Proteins

Amino acids

Sugars

Nucleotides

Fatty acidsGlyceraldehyde-3-P

Acetyl CoA

Pyruvate

CATABOLISM

Glu

PheLys

Ala

ValGlucose

Precursormolecules

Macromolecules

Bacterialcell

Buildingblocks

Checklist of Enzyme Characteristics

Enzymes: Catalyzing the Chemical Reactions of Life

•Enzymes -are catalysts that increase the rate of chemical

reactions without becoming part of the products or being consumed in the reaction

-substrates: reactant molecules acted on by an enzyme

-Have unique active site on the enzyme that fits only the substrate

Enzyme Structure

•Simple enzymes consist of protein alone

•Conjugated enzymes contain protein and nonprotein molecules

-sometimes referred to as a holoenzyme

-apoenzyme: protein portion of a conjugated enzyme

-cofactors: inorganic elements (metal ions)

-coenzymes: organic cofactor molecules

Conjugated Enzyme Structure


CoenzymeCoenzyme

Metalliccofactor

ApoenzymesMetalliccofactor

Enzyme-Substrate Interactions

•A temporary enzyme-substrate union must occur at the active site

-fit is so specific that it is described as a “lock-and-key” fit

•Bond formed between the substrate and enzyme are weak and easily reversible

•Once the enzyme-substrate complex has formed, an appropriate reaction occurs on the substrate, often with the aid of a cofactor

•Product is formed

•Enzyme is free to interact with another substrate

Enzyme-Substrate Reactions


E

Substrates

Enzyme (E)Doesnot fit

(a) (b)

ES complex

(c)

Products

How Enzymes Work

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Cofactors: Supporting the Work of Enzymes

•The need of microorganisms for trace elements arises from their roles as cofactors for enzymes

-iron, copper, magnesium, manganese, zinc, cobalt, selenium, etc.

•Participate in precise functions between the enzyme and substrate

-help bring the active site and substrate close together

-participate directly in chemical reactions with the enzyme-substrate complex

Cofactors: Supporting the Work of Enzymes (cont’d)

•Coenzymes-organic compounds that work in conjunction

with an apoenzyme

-general function is to remove a chemical group from one substrate molecule and add it to another substrate molecule

-carry and transfer hydrogen atoms, electrons, carbon dioxide, and amino groups

-many derived from vitamins

Classification of Enzyme Functions

•Enzymes are classified and named according to characteristics such as site of action, type of action, and substrate

-prefix or stem word derived from a certain characteristic, usually the substrate acted upon or type of reaction catalyzed

-ending –ase

Classification of Enzyme Functions (cont’d)

•Six classes of enzymes based on general biochemical reaction

-oxidoreductases: transfer electrons from one substrate to another, dehydrogenases transfer a hydrogen from one compound to another

-transferases: transfer functional groups from one substrate to another

-hydrolases: cleave bonds on molecules with the addition of water


•Six classes of enzymes based on general biochemical reaction (cont’d)

-lyases: add groups to or remove groups from double-bonded substrates

-isomerases: change a substrate into its isomeric form

-ligases: catalyze the formation of bonds with the input of ATP and the removal of water


•Each enzyme also assigned a common name that indicates the specific reaction it catalyzes

-carbohydrase: digests a carbohydrate substrate

-amylase: acts on starch

-maltase: digests maltose

-proteinase, protease, peptidase: hydrolyzes the peptide bonds of a protein

-lipase: digests fats

-deoxyribonuclease (DNase): digests DNA

-synthetase or polymerase: bonds many small molecules together

Regulation of Enzyme Function

•Constitutive enzymes: always present in relatively constant amounts regardless of the amount of substrate

•Regulated enzymes: production is turned on (induced) or turned off (repressed) in responses to changes in concentration of the substrate

Regulated EnzymesConstitutive Enzymes

Add moresubstrate.

Enzyme is induced.

or

Enzyme is repressed.

Removesubstrate.

(b)

(a)

Add moresubstrate.

No change inamount of enzyme.


Regulation of Enzyme Function (cont’d)

•Activity of enzymes influenced by the cell’s environment

-natural temperature, pH, osmotic pressure

-changes in the normal conditions causes enzymes to be unstable or labile

•Denaturation-weak bonds that maintain the native shape of

the apoenzyme are broken

-this causes disruption of the enzyme’s shape

-prevents the substrate from attaching to the active site

Metabolic Pathways

•Often occur in a multistep series or pathway, with each step catalyzed by an enzyme

•Product of one reaction is often the reactant (substrate) for the next, forming a linear chain or reaction

•Many pathways have branches that provide alternate methods for nutrient processing

•Others have a cyclic form, in which the starting molecule is regenerated to initiate another turn of the cycle

•Do not stand alone; interconnected and merge at many sites

Patterns of Metabolism


A

B

C

D

E

U

O2

O

O1

M

N

P

Q

R

M

A

B

C

N

X

Y

Z

V

W

X

Z

Y

Multienzyme Systems

Branched

Convergent

Linear Cyclic

Example:Glycolysis

Example:Amino acidsynthesis

T input

KrebsCycle

S product

Divergent

Biochemical Pathway


Direct Controls on the Action of Enzymes

•Competitive inhibition-inhibits enzyme activity by supplying a

molecule that resembles the enzyme’s normal substrate

-“mimic” occupies the active site, preventing the actual substrate from binding

•Noncompetitive inhibition-enzymes have two binding sites: the active site

and a regulatory site

-molecules bind to the regulatory site

-slows down enzymatic activity once a certain concentration of product is reached

Two Common Control Mechanisms for EnzymesCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Competitive Inhibition Noncompetitive Inhibition

SubstrateCompetitiveinhibitor withsimilar shape

Active site

Regulatory site

Normalsubstrate

Both moleculescompete forthe active site.

Enzyme

Reaction proceeds. Reaction is blockedbecause competitiveinhibitor is incapableof becoming a product.

Product

Reaction proceeds. Reaction is blocked becausebinding of regulatory moleculein regulatory site changesconformation of active site sothat substrate cannot enter.

Regulatorymolecule(product)

Enzyme

Controls on Enzyme Synthesis

•Enzymes do not last indefinitely; some wear out, some are degraded deliberately, and some are diluted with each cell division

•Replacement of enzymes can be regulated according to cell demand

•Enzyme repression: genetic apparatus responsible for replacing enzymes is repressed

-response time is longer than for feedback inhibition

•Enzyme induction: enzymes appear (are induced) only when suitable substrates are present

Enzyme RepressionCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1

2

3

4

5

6

7

= +

RNA translated into protein

DNA transcribed into RNA

Protein

Excess product binds toDNA and shuts downfurther enzyme production. DNA can not be transcribed;

the protein cannot be made.

Substrate

Folds to form functionalenzyme structure

EnzymeProducts Substrate

Enzyme Induction in E. coli

•If E. coli is inoculated into a medium containing only lactose, it will produce the enzyme lactase to hydrolyze it into glucose and galactose

•If E. coli is subsequently inoculated into a medium containing only sucrose, it will cease to synthesizing lactase and begin synthesizing sucrase

•Allows the organism to utilize a variety of nutrients, and prevents it from wasting energy by making enzymes for which no substrates are present

Concept Check

Which of the following mechanisms of enzyme control blocks a reaction catalyzed by an enzyme, by the binding of a product to a regulatory site on the enzyme?

A. enzyme repressionB. competitive inhibitionC. enzyme inductionD. noncompetitive inhibitionE. None of the choices is correct.


6. Name the chemical in which energy is stored in cells.

7. Create a general diagram of a redox reaction.

8. Identify electron carriers used by cells.

Energy in Cells

•Energy is managed in the form of chemical reactions that involve the making and breaking of bonds and the transfer of electrons

•Exergonic reactions release energy, making it available for cellular work

•Endergonic reactions are driven forward with the addition of energy

•Exergonic and endergonic reactions are often coupled so that released energy is immediately put to work

Oxidation and Reduction

•Oxidation: loss of electrons-when a compound loses electrons, it is oxidized

•Reduction: gain of electrons-when a compound gains electrons, it is reduced

•Oxidation-reduction (redox) reactions are common in the cell and are indispensable to the required energy transformations

Oxidation and Reduction (cont’d)

•Oxidoreductases: enzymes that remove electrons from one substrate and add them to another

-their coenzyme carriers are nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD)

•Redox pair: an electron donor and an electron acceptor involved in a redox reaction

Redox PairsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

-+

Na 2 8 7Cl2 8 1

Oxidizing agentaccepts electrons.

Reducing agentgives up electrons.

Na 2 8 2 8 8Cl

Oxidizedcation

Reducedanion

Oxidation and Reduction (cont’d)

•Energy present in the electron acceptor can be captured to phosphorylate (add an inorganic phosphate) to ADP or to some other compound to store energy in ATP

•The cell does not handle electrons as discrete entities but rather as parts of an atom such as hydrogen (consisting of a single electron and a single proton)

•Dehydrogenation: the removal of hydrogen during a redox reaction

Electron Carriers: Molecular Shuttles

•Electron carriers resemble shuttles that are alternately loaded and unloaded, repeatedly accepting and releasing electrons and hydrogens to facilitate transfer of redox energy

H+

P

P

P

P

H++NAD+ NAD H

Reduced Nicotinamide

From substrate

Oxidized Nicotinamide

Adenine

Ribose

NH2

2H2e:

H

C

C C

C C

O

CH

NH2

H

C

C C

C C

O

C

N N


ATP: Metabolic Money•Three-part molecule

-nitrogen base (adenine)

-5-carbon sugar (ribose)

-chain of three phosphate groups bonded to ribose

-phosphate groups are bulky and carry negative charges, causing a strain between the last two phosphates

-the removal of the terminal phosphate releases

energy

N

NN

N N

H H

H

H

O

HHH H

O

O

O

O

P O

O

H

HPP

Adenine

AdenosineAdenosine

Diphosphate(ADP)

AdenosineTriphosphate

(ATP)

HO

OH OH OH

OH

Ribose

OHBond that releasesenergy when broken


Concept Check

In a redox reaction, loss of electrons is

A. phosphorylation.B. oxidation.C. fermentation.D. reduction.E. None of the choices is correct.


9. Name three basic catabolic pathways, and give an estimate of how much ATP each of them yields.

10. Write a summary statement describing glycolysis.

11. Describe the Krebs cycle.

12. Discuss the significance of the electron transport system.

13. Point out how anaerobic respiration differs from aerobic respiration.

14. Provide a summary of fermentation.

15. Describe how noncarbohydrate compounds are catabolized.

Catabolism

•Metabolism uses enzymes to catabolize organic molecules to precursor molecules that cells then use to anabolize larger, more complex molecules

•Reducing power: electrons available in NADH and FADH2

•Energy: stored in the bonds of ATP

-both are needed in large quantities for anabolic metabolism

-both are produced during catabolism

How the NAD+ Works


Overview of the Three Main Catabolic Pathways


Fermentation

ANAEROBIC RESPIRATION FERMENTATION

ATP ATP

AEROBIC RESPIRATION

CO2

NAD H

ATP

CO2

NAD H

ATP

NAD HCO2

ATPFADH2

Using organiccompounds as

electron acceptor

Electron Transport System Electron Transport System

Alcohols, acids

2 ATPs2–36 ATPs36–38 ATPsMaximum net yield

Yields variableamount ofenergy

Yields 2 GTPs

Yields 2 ATPs

CO2

NAD H

ATP

NAD H

FADH2 ATP

CO2

KrebsCycle

KrebsCycle

Using O2 as electron acceptor Using non- O2 compound as electron acceptor

(So42–, NO3–, CO3

2–)

Gly

co

lys

is

Gly

co

lys

is

Gly

co

lys

is

Getting Materials and Energy

•Nutrient processing in bacteria is extremely varied, but in most cases the nutrient is glucose

•Aerobic respiration-a series of reactions that converts glucose to

CO2 and allows the cell to recover significant amounts of energy

-utilizes glycolysis, the Krebs cycle, and the electron transport chain

-relies on free oxygen as the final electron and hydrogen acceptor

-characteristic of many bacteria, fungi, protozoa, and animals

Getting Materials and Energy (cont’d)

•Anaerobic respiration -used by strictly anaerobic organisms and those who

are able to metabolize with or without oxygen

-involves glycolysis, the Krebs cycle, and the electron transport chain

-uses NO3-, SO4

2-, CO33-, and other oxidized

compounds as final electron acceptors

•Fermentation-incomplete oxidation of glucose

-oxygen is not required

-organic compounds are final electron acceptors

Glycolysis

•Turns glucose into pyruvate, which yields energy in the pathways that follow


Table 7.2

One reaction breaks fructose-1,6-diphosphateinto two 3-carbon molecules.

Five reactions convert each 3 carbon moleculeinto the 3C pyruvate.

Pyruvate is a molecule that is uniquely suited for chemicalreactions that will produce reducing power (which willeventually produce ATP).

C C C C C C

Fructose-1, 6-diphosphate

C C C C C C

C C CC C C

C C CC C C

Glycolysis

Energy Lost or Gained

Uses 2 ATPs

Overview Details

Three reactions alter and rearrange the6-C glucose molecule into 6-C fructose-1,6diphosphate.

Yields 4 ATPs and 2 NADHs

Total Energy Yield: 2 ATPs and2 NADHs

Glucose

Pyruvate Pyruvate

How Glycolysis Works


The Krebs Cycle (Citric Acid Cycle):A Carbon and Energy Wheel

•After glycolysis, pyruvic acid is still energy-rich

•cytoplasm of bacteria and mitochondrial matrix of eukaryotes-a cyclical metabolic pathway that begins with acetyl CoA,

which joins with oxaloacetic acid, and then participates in seven other additional transformations

-transfers the energy stored in acetyl CoA to NAD+ and FAD by reducing them (transferring hydrogen ions to them)

-NADH and FADH2 carry electrons to the electron transport chain

-2 ATPs are produced for each molecule of glucose through phosphorylation

The Krebs Cycle


Table 7.3

Each acetyl CoA yields 1 GTP, 3 NADHs,1 FADH, and 2 CO2 molecules.

Total Yield per 2 acetyl CoAs:CO2: 4 In the course of seven more

reactions, citrate is manipulatedto yield energy and CO2 andoxaloacetate is regenerated.

Intermediate molecules on thewheel can be shunted into othermetabolic pathways as well.

In the first reaction, acetyl CoAdonates 2Cs to the 4C moleculeoxaloacetate to form 6C citrate.

C C C

Energy: 2 GTPs, 6 NADHs, 2 FADHs

Pyruvate

CC CC CC

Details

The Krebs Cycle

Energy Lost or Gained Overview

Pyruvate

The 3C pyruvate is converted to2C acetyl CoA in one reaction.

Otherintermediates GTP

CO2

CO2

Yields:3 NADHs1 FADH2

Citrate

Oxaloacetate

Acetyl CoA

Remember: Thishappens twice for

each glucosemolecule that

enters glycolysis.

One CO2 is liberated and one NADH isformed.

C C C C

C C C C C C

C CC

How the Krebs Cycle Works


The Respiratory Chain: Electron Transport

•A chain of special redox carriers that receives reduced carriers (NADH, FADH2) generated by glycolysis and the Krebs cycle

-passes them in a sequential and orderly fashion from one to the next

-highly energetic

-allows the transport of hydrogen ions outside of the membrane

-in the final step of the process, oxygen accepts electrons and hydrogen, forming water

The Respiratory Chain:Electron Transport (cont’d)

•Principal compounds in the electron transport chain:-NADH dehydrogenase

-flavoproteins

-coenzyme Q (ubiquinone)

-cytochromes

•Cytochromes contain a tightly bound metal ion in their center that is actively involved in accepting electrons and donating them to the next carrier in the series

The Respiratory (Electron Transport) ChainCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Table 7.4

Reduced carriers (NADH, FADH) transfer electrons and H+ to firstelectron carrier in chain: NADH dehydrogenase.

These are then sequentially transferred to the next four to sixcarriers with progressively more positive reduction potentials.The carriers are called cytochromes. The number of carriers varies,depending on the bacterium.

Simultaneous with the reduction of the electron carriers,protons are moved to the outside of the membrane, creating aconcentration gradient (more protons outside than inside thecell). The extracellular space becomes more positively chargedand more acidic than the intracellular space. This conditioncreates the proton motive force, by which protons flow down theconcentration gradient through the ATP synthase embedded in themembrane. This results in the conversion of ADP to ATP.

Once inside the cytoplasm, protons combine with O2 toform water (in aerobic respirers [left]), and with a variety ofO-containing compounds to produce more reduced compounds.

Anaerobic respiration yields less per NADH and FADH.

Aerobic respiration yields a maximum of 3 ATPs peroxidized NADH and 2 ATPs per oxidized FADH.

The Respiratory (Electron Transport) Chain

Anaerobicrespirers

Aerobicrespirers

CytoplasmH2O NO2

– HS–

O2

H+

CellmembraneWith ETS

Cell wall

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

Cytochromes

NAD H

ATPADP

ATPsynthase

NO3–

SO42–

The Electron Transport Chain (cont’d)

•Electron transport carriers and enzymes are embedded in the cell membrane in prokaryotes and on the inner mitochondrial membrane in eukaryotes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Intermembranespace

CristaeH+ ions

The Electron Chain (cont’d)

•Released energy from electron carriers in the electron transport chain is channeled through ATP synthase

•Oxidative phosphorylation: the coupling of ATP synthesis to electron transport

-each NADH that enters the electron transport chain can give rise to 3 ATPs

-Electrons from FADH2 enter the electron transport chain at a later point and have less energy to release, so only 2 ATPs result

The Terminal Step

•Aerobic respiration-catalyzed by cytochrome aa3, also known as

cytochrome oxidase

-adapted to receive electrons from cytochrome c, pick up hydrogens from solution, and react with oxygen to form water

2H+ + 2e- + ½ O2 H20

The Terminal Step (cont’d)

•Most eukaryotes have a fully functioning cytochrome system

•Bacteria exhibit wide-ranging variations in this system-some lack one or more redox steps

-several have alternative electron transport schemes

-lack of cytochrome c oxidase is useful in differentiating among certain genera of bacteria


•A potential side reaction of the respiratory chain is the incomplete reduction of oxygen to the superoxide ion (O2

-) and hydrogen peroxide (H2O2)

•Aerobes produce enzymes to deal with these toxic oxygen products

-superoxide dismutase

-catalase

-Streptococcus lacks these enzymes but still grows well in oxygen due to the production of peroxidase

Electron Transport System and ATP Synthesis



•Anaerobic Respiration-the terminal step utilizes oxygen-containing

ions, rather than free oxygen, as the final electron acceptor

Nitrate reductase

NO3- + NADH NO2

- + H2O + NAD+

•Nitrate reductase catalyzes the removal of oxygen from nitrate, leaving nitrite and water as products

Anaerobic Respiration (cont’d)

•Denitrification-some species of Pseudomonas and Bacillus

possess enzymes that can further reduce nitrite to nitric oxide (NO), nitrous oxide (N2O), and even nitrogen gas (N2)

-important step in recycling nitrogen in the biosphere

•Other oxygen-containing nutrients reduced anaerobically by various bacteria are carbonates and sulfates

•None of the anaerobic pathways produce as much ATP as aerobic respiration

After Pyruvic Acid II: Fermentation

•Fermentation-the incomplete oxidation of glucose or other

carbohydrates in the absence of oxygen

-uses organic compounds as the terminal electron acceptors

-yields a small amount of ATP

-used by organisms that do not have an electron transport chain

-other organisms revert to fermentation when oxygen is lacking

Fermentation (cont’d)

•Only yields 2 ATPs per molecule of glucose

•Many bacteria grow as fast as they would in the presence of oxygen due to an increase in the rate of glycolysis

•Permits independence from molecular oxygen-allows colonization of anaerobic environments

-enables adaptation to variations in oxygen availability

-provides a means for growth when oxygen levels are too low for aerobic respiration

Fermentation (cont’d)

•Bacteria and ruminant cattle-digest cellulose through fermentation

-hydrolyze cellulose to glucose

-ferment glucose to organic acids which are absorbed as the bovine’s principal energy source

•Human muscle cells-undergo a form of fermentation that permits short

periods of activity after the oxygen supply has been depleted

-convert pyruvic acid to lactic acid, allowing anaerobic production of ATP

-accumulated lactic acid causes muscle fatigue

Fermentation


Table 7.5

Pyruvic acid from glycolysis can itself become the electronacceptor.

Pyruvic acid can also be enzymatically altered and then serve asthe electron acceptor.

The NADs are recycled to reenter glycolysis.

The organic molecules that became reduced in their role aselectron acceptors are extremely varied, and often yield usefulproducts such as ethyl alcohol, lactic acid, propionic acid,butanol, and others.

C C

O

H

H

H

H

CC C

H

H

H

H

O

C C

H

H

H

H

H

C C C

Lactic acid

OH

OH

NAD+

Ethyl alcohol

OH

Acetaldehyde

CO2

Pyruvic acid

Remember: Thishappens twice for

each glucosemolecule that

enters glycolysis.

Fermentation

NAD H NAD H

Products of Fermentation in Microorganisms

•Alcoholic beverages: ethanol and CO2

•Solvents: acetone, butanol

•Organic acids: lactic acid, acetic acid

•Vitamins, antibiotics, and hormones

•Large-scale industrial syntheses by microorganisms often utilize entirely different fermentation mechanisms for the production of antibiotics, hormones, vitamins, and amino acids

Catabolism of Noncarbohydrate Compounds

•Complex polysaccharides broken into component sugars, which can enter glycolysis

•Lipids broken down by lipases-glycerol converted to dihydroxyacetone

phosphate, which can enter midway into glycolysis

-fatty acids undergo beta oxidation, whose products can enter the Krebs cycle as acetyl CoA

Catabolism of Noncarbohydrate Compounds (cont’d)

•Proteins are broken down into amino acids by proteases

-amino groups are removed through deamination

-remaining carbon compounds are converted into Krebs cycle intermediates or decarboxylated

Concept Check

What is the maximum net yield of ATP per molecule of glucose for each of the following types of respiration?

A. aerobic respirationB. anaerobic respirationC. fermentation


16. Provide an overview of the anabolic stages of metabolism.

17. Define amphibolism.

Anabolism and the Crossing Pathways of Metabolism

•The Frugality of the Cell-cells have systems for careful management of

carbon compounds

-catabolic pathways contain strategic molecular intermediates (metabolites) that can be diverted into anabolic pathways

-a given molecule can serve multiple purposes; maximum benefit can be derived from all nutrients and metabolites of the cell pool

•Amphibolism: the ability of a system to integrate catabolic and anabolic pathways to improve cell efficiency

Amphibolic Pathways of Glucose MetabolismCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Table 7.6

Intermediates from glycolysis are fed into the aminoacid synthesis pathway. From there, the compounds areformed into proteins. Amino acids can then contributenitrogenous groups to nucleotides to form nucleic acids.

Glucose and related simple sugars are made intoadditional sugars and polymerized to form complexcarbohydrates.

The glycolysis product acetyl CoA can be oxidized to formfatty acids, critical components of lipids.

Catabolic PathwaysIn addition to the respiration and fermentation pathwaysalready described, bacteria can deaminate amino acids,which leads to the formation of a variety of metabolicintermediates, including pyruvate and acetyl CoA.

Also, fatty acids can be oxidized to form acetyl CoA.C

AT

AB

OL

ISM

AN

AB

OL

ISM

Gly

coly

sis

Amphibolic Pathways of Glucose Metabolism

Anabolic Pathways

Beta oxidationDeamination

GLUCOSE

Metabolicpathways

Simplepathways

Pyruvic acid

Acetyl coenzymeA

KrebsCycle

NH3 H2O

CO2

Building block

Macromolecule

Cellstructure

Membranesstorage

Cell wallstorage

Enzymes/Membranes

Chromosomes

Lipids/Fats

Starch/CelluloseProteins

Nucleicacids

Fatty acidsCarbohydratesAmino acidsNucleotides

Anabolism: Formation of Macromolecules

•Two possible sources for monosaccharides, amino acids, fatty acids, nitrogenous bases, and vitamins

-enter the cell from the outside as nutrients

-can be synthesized through various cellular pathways

Anabolism: Formation of Macromolecules (cont’d)

•The degree to which an organism can synthesize its own building blocks is genetically determined and varies from group to group

-autotrophs only require CO2 as a carbon source and a few minerals to synthesize all cell substances

-some heterotrophs such as E. coli can synthesize all cellular substances from a few minerals and one organic carbon source such as glucose

Carbohydrate Biosynthesis

•Glucose has a crucial role in bioenergetics-major component of cellulose cell walls and

certain storage molecules

-an intermediary in glycolysis, glucose-6-P is used to form glycogen

-peptidoglycan is a linked polymer derived from fructose-6-P from glycolysis

-the carbohydrates ribose and deoxyribose are essential building blocks of nucleic acids

-polysaccharides are the predominant components of capsules and glycocalyx

Amino Acids, Protein Synthesis, and Nucleic Acid Synthesis

•Proteins-account for a large proportion of a cell’s

constituents

-essential components of enzymes, cell membrane, cell wall, and cell appendages

-20 amino acids needed to make these proteins

-some organisms, such as E. coli, have pathways that will synthesize all 20 amino acids

-others, such as animals, lack some or all of the pathways for amino acid synthesis

Amino Acids, Protein Synthesis, and Nucleic Acid Synthesis (cont’d)

•Nucleic acids: DNA and RNA-responsible for the hereditary continuity of cells

and the direction of protein synthesis

-covered in more detail in chapter 8

Assembly of the Cell

•Component parts of bacteria are being synthesized on a continuous basis

•Catabolism is also taking place as long as nutrients are present and the cell is nondormant

•Cell division takes place when-anabolism produces enough macromolecules to

serve two cells

-DNA replication produces duplicate copies of the cell’s genetic material

-membrane and cell wall have increased in size

•Catabolic processes provide all of the energy for complex building reactions

Concept Check

The ability of a cell to integrate molecule-using and molecule-building pathways to improve cell efficiency is known as

A. anabolism.B. amphibolism.C. catabolism.D. metabolism.E. None of the choices is correct.

ch. 7 (microbial metabolism)

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