Microbial Physiology and Genetics

PART 1

Chapter 7

Microbial Physiology

Physiology – is the study of the vital life processes of organisms, especially how these processes normally function in living organisms

Microbial Physiology – concerns the vital life processes of microorganisms

Advantages of Using Bacteria

Inexpensive to maintain in the laboratory.

Take up little space and reproduce quickly.

Morphology, nutritional needs and metabolic reactions are easily observable.

NutrientsRefers to various chemical compounds that

organisms use to sustain life. Many nutrients are energy sources.Organisms will obtain energy from these

nutrients by breaking chemical bonds.When chemical bond is broken, energy is

released.Nutrients are broken down by enzymatic

actions.

Nutritional RequirementsSix major chemical elements: carbon,

hydrogen, oxygen, nitrogen, phosphorus and sulfur

Lesser amounts: sodium, potassium, chlorine, magnesium, calcium, iron, iodine, and some trace elements

Essential nutrients – materials that organisms are unable to synthesize, but are required for the building of macromolecules and sustaining life.

Categorizing Microorganisms According to Their Energy and Carbon Sources

Terms Relating to Energy SourcePhototrophs- use lightChemotrophs- use either inorganic or

organic chemicalsChemolithotrophs- use inorganic

chemicalsChemoorganotrophs- use organic

chemicals

Terms Relating to Organism’s Carbon SourceAutotrophs- use CO2 as their energy sourceHeterotrophs- use organic compounds as their

carbon source other than CO2

Photoautotrophs- use light energy and CO2 Photoheterotrophs- use light and organic

compounds other than CO2 Chemoautotrophs- use chemicals are energy

source and CO2 as carbon sourceChemoheterotrophs- use chemicals as energy

source and organic compound other than CO2 as energy source

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.

Ecology – is the study of the interaction between organisms and the world around them.

Ecosystem – refers to the interactions between living organisms and their nonliving environment.

Phototrophs are producers of food and oxygen for chemoheterotrophs.

Dead plants and animals would clutter the earth if chemoheterotrophic saprophytes and decomposers did not break down dead organic compounds.

Photoautotrophs contribute energy to the ecosystem by trapping energy from the sun and converting it to build organic compound.

Metabolic EnzymesMetabolism is the sum of the chemical

reactions in an organism, Metabolic reaction

Catabolism is the energy-releasing processes.

Anabolism is the energy-using processes.

Metabolic enzymes enhances and regulates metabolic reaction.

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

Metabolic pathways are determined by enzymes.

Enzymes are encoded by genes.

Biologic Catalysts

Biologic catalysts- protein that either causes a particular chemical reaction to occur or accelerates.

Substrate- particular substance in which enzymes act

Apoenzyme- protein (inactive)Cofactor- nonprotein component

Coenzyme- organic cofactor (activator)Holoenzyme- apoenzyme + cofactor

Kinds of Enzymes

Endoenzymes- produce within the cell that remains within the cell (digestive enzymes)

Exoenzymes- produce within the cell and released from the cell (cellulase)

Factors that Affects the Efficiency of Enzymes

Enzymes can be denatured by temperature and pH

Temperature

pH

Substrate concentration

Competitive Inhibition

Non-competitive Inhibition

Metabolism

Metabolite- any molecule that is a nutrient, an intermediary or end product of metabolism

Catabolism- breakdown of carbohydrates to release energy

Anabolism- assembly of smaller molecules to larger molecules

Metabolism

ATP is generated by the phosphorylation of ADP

Biochemical Pathways

Series of linked biochemical reactions that occur in a step-wise manner, leading from the starting material to the end product.

Glucose is the favorite “food” of cells, including microorganisms.

Nutrients- energy sourcesChemical bonds- stored energyWhenever chemical bonds within the nutrients are

broken, energy is released.Aerobic respiration and fermentation reactions.

Catabolism/Aerobic Respiration of Glucose

The breakdown of carbohydrates to release energyGlycolysisKrebs cycleElectron transport chain

Glycolysis

Glycolytic pathway, the Embden-Meyerhof pathway, Embden-Meyerhof-Parnas pathway.

A nine-step biochemical path, involving nine separate biochemical reactions, each of which requires specific enzymes.

Six-carbon molecule of glucose is broken down into three-carbon molecules of pyruvic acid.

Can take place with or without oxygen.Produces very little energy– only 2 ATP.Takes place in the cytoplasm of both prokaryptic

and eukaryotic cells.

Krebs CycleThe pyruvic acid molecules produced during

glycolysis are converted into acetyl-CoA molecules.

The Krebs Cycle is consists of eight separate reactions, each of which is controlled by a different enzymes.

Acetyl-CoA combine with oxalate to produce citric acid (tricarboxylic acid).

Only 2 ATP produced, but a number of products like NADH, FADH2, and H ions.

Mitochondria (eukaryotes); inner surface of cell membrane (prokaryotes).

Electron Transport Chain

Certain of the products produced during the Krebs cycle enter the electron transport chain.

Consist of a series of oxidation-reduction reactions, whereby energy is released as electrons are transferred from one compound to another.

Oxygen is at the end of the chain; referred to as then final or terminal electron acceptor.

Cytochrome oxidase- enzyme responsible for transferring electrons to oxygen.

Produces 32 ATP in prokaryotic cells, and 34 ATP in eukaryotic cells.

Net yield by aerobic respiration: 36 ATP (prokaryotic cells) and 38 ATP (eukaryotic cells).

Aerobic respiration of glucose produces 18-19X ATP than fermentation.

Biochemical Pathway

Prokaryotic Eukaryotic

Glycolysis 2 2

Krebs Cycle 2 2

ETC 32 34

Total ATP 36 38

Number of ATP Produced From One MoleculeOf Glucose by Aerobic Respiration

Pathway Eukaryote Prokaryote

Glycolysis Cytoplasm Cytoplasm

Intermediate step Cytoplasm Cytoplasm

Krebs cycle Mitochondrial matrix Cytoplasm

ETC Mitochondrial inner membrane

Plasma membrane

Fermentation of GlucoseDo not involve oxygenFirst step is glycolysisNext step is the conversion of pyruvic acid into an

end product.Does not use the Krebs cycle or ETCEnd product depends on specific organism

involved: Saccharomyces spp. and Zymomonas spp. convert

pyruvic acid to ethanol and CO2

Lactic acid bacteria convert pyruvic acid to lactic acid.

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 compoundsIn human muscle cells, lack of oxygen during

extreme exertion results in pyruvic acid being converted to lactic acid.

Fermentation produces only 2 ATPAerobes/facultative aerobes Vs. oblgate

anaerobes

Oxidation-reduction Reactions

Paired reactions in which electrons are transferred from one compound to another.

Oxidation- loss of one or more electronsReduction- gain of one or more electronsReducing agent- electron donorOxidizing agent- electron acceptor

Anabolism

Require energy to form chemical bonds.The energy is provided by the catabolic

reactions occurring simultaneously in the cell.Referred to as biosynthetic reactions.

PhotosynthesisChemosynthesis

PhotosynthesisPhoto: Conversion of light energy into chemical

energy (ATP)Light-dependent (light) reactions

Synthesis: Fixing carbon into organic moleculesLight-independent (dark) reaction, Calvin-Benson

cycleOxygenic:

6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2O

Anoxygenic: CO2 + 2 H2S + Light energy [CH2O] + 2 A + H2O

ChemosynthesisUse energy from chemicals.

Chemoautotroph, Thiobacillus ferroxidans

2Fe2+

2Fe3+

NAD+

NADH

ETC

ADP + P ATP

2 H+

Next topic: Microbial Genetics

Finish!