Microbial MetabolismCh 5

• Metabolism is the sum of the chemical reactions in an organism.

• Catabolism is the energy-releasing processes.

• Anabolism is the energy-using processes. (typically building something)

• Catabolism provides the building blocks and energy for anabolism.

Microbial Metabolism

Figure 5.1

• Are metabolic pathways that have both catabolic and anabolic functions.– This is basically all of life

Amphibolic pathways

Figure 5.32.1

Amphibolic pathways

Figure 5.32.2

• A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell.

• A primary metabolic pathway are the reactions that do the basic work of the cell. Get food and grow

• Metabolic pathways are determined by enzymes.

• Enzymes are encoded by genes.

Biochemical tests

Figure 10.8

• Used to identify bacteria.

• Enzymes are genes

• Sum of genes is your organism

Enzymes

Figure 5.2

• Biological catalysts– Specific for a chemical reaction; not used up in

that reaction

• Apoenzyme: protein

• Cofactor: Nonprotein component– Coenzyme: Organic cofactor

• Holoenzyme: Apoenzyme + cofactor

Enzymes

Enzymes

Figure 5.3

• NAD+

• NADP+

• FAD

• Coenzyme A

• Biotin

• Folic acid

• Many of the vitamins

Important Coenzymes

• The turnover number is generally 1-10,000 molecules per second.

Enzymes

Figure 5.4

• Enzymes can be denatured by temperature and pH

Factors Influencing Enzyme Activity

Figure 5.6

• Temperature

Factors Influencing Enzyme Activity

Figure 5.5a

• pH

Factors Influencing Enzyme Activity

Figure 5.5b

• Substrate concentration

Factors Influencing Enzyme Activity

Figure 5.5c

• Competitive inhibition

Factors Influencing Enzyme Activity

Figure 5.7a, b

Factors Influencing Enzyme Activity

Sulfa inhibits the enzyme that uses PABA for synthesis of folic acid

• Noncompetitive inhibition

Factors Influencing Enzyme Activity

Figure 5.7a, c

• Feedback inhibition

Figure 5.8

• ATP is generated by the phosphorylation of ADP.

The Generation of ATP

• Substrate-level phosphorylation is the transfer of a high-energy PO4

- to ADP.

The Generation of ATP

• Energy released from the transfer of electrons (oxidation) of one compound to another (reduction) is used to generate ATP by chemiosmosis.

The Generation of ATP

Metabolic Pathways

• The breakdown of carbohydrates to release energy– Glycolysis– Krebs cycle– Electron transport chain

Carbohydrate Catabolism

• The oxidation of glucose to pyruvic acid, produces ATP and NADH.

Glycolysis

• 2 ATPs are used

• Glucose is split to form 2 Glyceraldehyde-3-phosphate

Preparatory Stage

Figure 5.12.1

PreparatoryStage

Glucose

Glucose6-phosphate

Fructose6-phosphate

Fructose1,6-diphosphate

Dihydroxyacetonephosphate (DHAP)

Glyceraldehyde3-phosphate(GP)

1

2

3

4

5

• 2 Glucose-3-phosphate oxidized to 2 Pyruvic acid

• 4 ATP produced

• 2 NADH produced

Energy-Conserving Stage

Figure 5.12.2

1,3-diphosphoglyceric acid

3-phosphoglyceric acid

2-phosphoglyceric acid

Phosphoenolpyruvic acid(PEP)

6

7

8

9

10

Pyruvic acid

• Glucose + 2 ATP + 2 ADP + 2 PO4– + 2

NAD+ 2 pyruvic acid + 4 ATP + 2 NADH + 2H+

Glycolysis

• Pentose phosphate pathway:– Uses pentoses and NADPH– Operates with glycolysis– Use and production of 5 carbon sugars (na)– Bacillus subtilis, E. coli, Enterococcus faecalis

• Entner-Doudoroff pathway: – Produces NADPH and ATP– Does not involve glycolysis– Pseudomonas, Rhizobium, Agrobacterium

Alternatives to Glycolysis

• Oxidation of molecules liberates electrons for an electron transport chain

• ATP generated by oxidative phosphorylation

Cellular Respiration

• Pyruvic acid (from glycolysis) is oxidized and decarboyxlated

Intermediate Step

Figure 5.13.1

• Oxidation of acetyl CoA produces NADH and FADH2

Krebs Cycle

Krebs Cycle

Figure 5.13.2

• A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain.

• Energy released can be used to produce ATP by chemiosmosis.

The Electron Transport Chain

Chemiosmosis

Figure 5.15

Electron transport and Chemiosmosis

Figure 5.16.2

Figure 5.14

• Aerobic respiration: The final electron acceptor in the electron transport chain is molecular oxygen (O2).

• Anaerobic respiration: The final electron acceptor in the electron transport chain is not O2. Yields less energy than aerobic respiration because only part of the Krebs cycles operations under anaerobic conditions.

Respiration

Anaerobic respiration

Electron acceptor Products

NO3– NO2

–, N2 + H2O

SO4– H2S + H2O

CO32 – CH4 + H2O

• Energy produced from complete oxidation of 1 glucose using aerobic respiration

Pathway ATP produced

NADH produce

d

FADH2 produce

d

Glycolysis 2 2 0

Intermediate step 0 2

Krebs cycle 2 6 2

Total 4 10 2

• ATP produced from complete oxidation of 1 glucose using aerobic respiration

• 36 ATPs are produced in eukaryotes.

Pathway

By substrate-level

phosphorylation

By oxidative phosphorylation

From NADH

From FADH

Glycolysis 2 6 0Intermediate step 0 6

Krebs cycle 2 18 4Total 4 30 4

Pathway Eukaryote Prokaryote

Glycolysis Cytoplasm Cytoplasm

Intermediate step Cytoplasm Cytoplasm

Krebs cycle Mitochondrial matrix Cytoplasm

ETC Mitochondrial inner membrane

Plasma membrane

• Releases energy from oxidation of organic molecules

• Does not require oxygen

• Does not use the Krebs cycle or ETC

• Uses an organic molecule as the final electron acceptor

Fermentation

Fermentation

Figure 5.18b

• Alcohol fermentation. Produces ethyl alcohol + CO2

• Lactic acid fermentation. Produces lactic acid.– Homolactic fermentation. Produces lactic acid

only.– Heterolactic fermentation. Produces lactic

acid and other compounds.

Fermentation

Fermentation

Figure 5.19

Fermentation

Figure 5.23

Production of acid and gas

Lipid Catabolism

Figure 5.20

Protein Catabolism

Protein Amino acidsExtracellular proteases

Krebs cycleDeamination, decarboxylation, dehydrogenation

Organic acid

Biochemical tests

Figure 10.8

• Used to identify bacteria.

• Halobacterium uses bacteriorhodopsin, not chlorophyll, to generate electrons for a chemiosmotic proton pump.

Chemotrophs• Use energy from chemicals.

– Chemoheterotroph

• Energy is used in anabolism.

Glucose

Pyruvic acid

NAD+

NADH

ETC

ADP + P ATP

Chemotrophs• Use energy from chemicals.

– Chemoautotroph, Thiobacillus ferroxidans

• Energy used in the Calvin-Benson cycle to fix CO2.

2Fe2+

2Fe3+

NAD+

NADH

ETC

ADP + P ATP

2 H+

Metabolic Diversity Among Organisms

Nutritional type Energy source

Carbon source Example

Photoautotroph Light CO2Oxygenic: Cyanobacteria plants.Anoxygenic: Green, purple bacteria.

Photoheterotroph Light Organic compounds

Green, purple nonsulfur bacteria.

Chemoautotroph Chemical CO Iron-oxidizing bacteria.

Chemoheterotroph Chemical Organic compounds

Fermentative bacteria.Animals, protozoa, fungi, bacteria.

• Polysaccharide Biosynthesis

Metabolic Pathways of Energy Use

Figure 5.28

• Lipid Biosynthesis

Metabolic Pathways of Energy Use

Figure 5.29

• Amino Acid and Protein Biosynthesis

Metabolic Pathways of Energy Use

Figure 5.30a

Metabolic Pathways of Energy Use

Figure 5.30b

•Amino Acid and Protein Biosynthesis

• Purine and Pyrimidine Biosynthesis

Metabolic Pathways of Energy Use

Figure 5.31

• Are metabolic pathways that have both catabolic and anabolic functions.

Amphibolic pathways

Figure 5.32.1

Amphibolic pathways

Figure 5.32.2