Biology 1009Microbiology-Summer 2003

Johnson

Unit 2Chapters 5, 6, 7, and 14

Chapter 5Microbial Metabolism

Metabolism-sum of all chemical reactions within living organismsTwo types:1) Catabolism (catabolic)Ø Breakdown of complex organic molecules into

simpler compoundsØ Release energy

2) Anabolism (anabolic)Ø The building of complex organic molecules from

simpler onesØ Requires energy

Enzymes-proteins (catalysts) that speed up and direct chemical

reactionsEnzymes are substrate specificl Lipase lipidl Sucrase sucrosel Urease ureal Protease proteinl Dnase DNA

Enzymes have 3 D shapeEnzymes are efficient and work at low temps

Enzyme Specificity

Explained by Lock and Key Theory

E + S ---à ES ----à E + P

Naming Enzymes-most named by adding “ase” to substrate

Maltose MaltaseLipids LipaseProteins ProteaseRemove a “P” PhosphataseRemove a “H” Dehydrogenase

Naming Enzymes-Classes

Grouped based on the type of reaction they catalyze

1) Oxidoreductase=electrons gained or lost

2) Hydrolases=catalyze hydrolysis3) Ligases=join two molecules

(synthesis)

Enzyme Components

Two portionsl Apoenzyme-protein portionl Coenzyme-non-protein

Holoenzyme-entire enzyme

Coenzymes

Many derived from vitaminsImportant examples:l Niacin-NAD (nicotinamide adenine

dinucleotide)l Riboflavin-FAD (flavin adenine

dinucleotide)*Both have roles in ETS

Factors Influencing Enzymatic Activity

Temperature-drastic increase may cause denaturationpH-extreme pH may denature enzymesSubstrate concentration-enzyme activity increases as substrate { } increases until saturation occursInhibitors-two main typesl Competitive and noncompetitive

Temperature, pH, and substrate concentration

Competitive Inhibitors

Compete with substrate for active siteTwo types:

1) Irreversible2) Reversible

Examples:l Penicillin

l Compete for the active site on the enzyme involved with the synthesis of the amino acidcrossbridge in the bacterial cell wall

Noncompetitive Inhibitors

Attach to an allosteric site of enzyme, not the active site

Energy Production

Oxidation-Reduction Reactions1) Oxidation-loss of electrons from an atom

or molecule2) Reduction-molecule or atom gains an

electron

*As one substance in oxidized, another is simultaneously reduced

Oxidation-reduction

Generation of ATP

Phosphorylation-generation of ATP that occurs when a phosphate group is added to an organic moleculeThree Mechanisms of Phosphorylation

1) Substrate Level Phosphorylation-P directly added to ADP

2) Oxidative Phosphorylation-ETS(chemiosmosis)3) Photophosphorylation-ETS in plants

Carbohydrate Catabolism

Microbes oxidize carbohydrates as their primary source of energyMost common sourceàglucoseEnergy obtained from glucose via two main mechanisms:

1) Respiration2) Fermentation

Aerobic Cellular Respiration

Electrons released by oxidation and are passed down ETS (electron transport system) with oxygen being the final electron acceptorGeneral equation:l Glucose + oxygen --à carbon dioxide +

water + ATP

Respiration-Chemical Equation

C6H12O6 + 6 O2à 6 CO2 + 6 H2O + 38 ATP

Aerobic Cellular Respiration

Four subpathways

1) Glycolysis2) Transition Reaction3) Kreb’s Cycle4) Electron Transport System

Glycolysis

Splitting of sugar (6 carbons)Oxidation of glucose molecule into 2 molecules of pyruvic acid (3 carbons)

End productsl 2 pyruvic acid moleculesl 2 NADHl 2 ATP

Summary of Glycolysis

Transition Reaction

Connects glycolysis to the Kreb’s Cycle

End Productsl 2 Acetyl CoEnzyme Al 2 Carbon dioxide moleculesl 2 NADH

Krebs Cycle(Citric Acid Cycle)

Series of chemical reactions that begin and end with citric acid (6 carbons)

End productsl 2 ATP l 6 NADHl 2 FADH2

l 4 CO2

Krebs Cycle

Electron Transport System

Occurs within the cell membrane of prokaryotesElectrons transferred from compound to compound, generating ATP via oxidative phosphorylation =Chemiosmotic Model of ATP Synthesisl Yields 34 ATP for each glucose molecule

ETS

Chemiosmotic Generation of ATP

Uses proton gradient l Energy produced from movement of

protons across cell membrane used by ATP synthase (protein channel) to make ATP from ADP and “P”

Chemiosmosis

Summary of ATP Production from ETS

3 ATP for each NADH2 ATP for each FADH2

l NADH FADH2

Ø Glycolysis 2 0Ø Transition 2 0Ø Krebs Cycle 6 2Total= 10 210 times 3 = 30 ATP 2 times 2 = 4 ATP

Total ATP Production for the complete oxidation of 1 glucose

in aerobic respiration

ATPGlycolysis 2Transition Reaction 0Krebs cycle 2ETS 34

l Total 38 ATP

Summary of Aerobic Respiration in Prokaryotes

Anaerobic Respiration

Electrons released by oxidation are passed down an ETS but oxygen is not the final electron acceptorl Final electron acceptors:

l Nitratel Sulfatel Carbonate

l Note: Lower amts of ATP produced

Fermentation

Anaerobic process that does not utilize the ETS or the Krebs Cycle.Usually involves the incomplete oxidation of a carbohydrate which then becomes the final electron acceptor.Involves glycolysis plus an additional stepYields many different end products

Lactic Acid Fermentation

Involved in food spoilageInvolved in food production (yogurt, milk, pickles)Two genera= Streptococcus/LactobacillusTwo steps:l Step 1=Glycolysis-1 glucose broken down into 2

pyruvic acid molecules + 2 ATPl Step 2=Reduction of 2 molecules of pyruvic acid

into 2 molecules of lactic acid

Alcohol Fermentation

Only 2 ATPEnd products: alcohol + carbon dioxideUsed to make alcoholic beverages & it makes bread dough riseExample= yeast (Saccharomyces cerevisiae)Three steps:l Glycolysis-yields 2 ATP & 2 pyruvic acidl 2 pyruvic acid broken down into 2 molecules

aldehyde and 2 CO2l 2 aldehyde reduced into 2 ethanol molecules

Types of Fermentation

Lipid Catabolism

Lipase breaks down lipid into glycerol and fatty acidsl Glycerol-converted into DHAP and

catabolized via glycolyis and the Krebs Cycle

l Fatty acids-undergo beta oxidation to produce Acetyl CoA, which is catabolized via Krebs Cycle

Lipid Catabolism

Protein Catabolism

Proteins too large to pass through cell membraneProteases and peptidases produced by microbe to break proteins and peptides into amino acidsAmino acids then enzymatically converted to substances that can enter Krebs Cycle

Catabolism of Organic Foods

Photosynthesis

Conversion of light energy from the sun into chemical energyChemical energy used to reduce CO2 into sugarInvolved in carbon fixation-recycling of carbon in the environment (living organisms rely on this)Photosynthesis-occurs in plants, algae, and cyanobacteria

Photosynthesis-Two Parts

Light Reaction-Light energy converts ADP and P into ATP via photophosphorylationl Two types of photophosphorylation: cyclic &

noncyclicl Chlorophyll from plants contain electrons that go

through ETS to make ATP

Dark Reaction-No light required-CO2 fixed to produce glucose

General Chemical Equationl 6 CO2 + 12 H2O + sun à C6H12O6 + 6 O2 + 6 H2O

Cyclic Photophosphorylation

Noncyclic Photophosphorylation