PRIMARY METABOLISM

FUNCTIONS OF METABOLISM

ANABOLIC

• Change nutrients into structural and functional components of the organism

CATABOLIC

• Extract chemical energy or nutrient element such as N and S from complex nutrients to provide E and materials for anabolic reactions

Anabolism depends on catabolism for E in the form of NADH, ATP and NADPH.

Also for the production of key intermediates for functional macromolecules synthesis

Primary Metabolism

The metabolic events that are important to functions of fungus in pure culture

Secondary metabolism coextensive with primary metabolism

The division into primary and secondary depends on the distribution of the metabolites among the organisms.

Eg of metabolites?

Organic acid, vitamin, antibiotics etc.

Carbon and Energy Metabolism

Glucose metabolism

Non-carbohydrates function as sole sources of C, must be convertable to glucose by a process called gluconeogenesis

Provide precursors for cell wall , glycoproteinsand other materials derived directly from hexoses.

Glycolysis

Glycolysis:

the breakdown of glucose by enzymes, releasing energy and pyruvic acid

3 pathways for hexoses:

1. EM (Embden-Meyerhof-Parnas)2. HM (Hexose monophosphate )3. ED (Entner-Doudoroff)

Glycolysis of Pentoses

2 pathways:

1. XP (xylitol pathway)

2. PK (phosphoketolase pathway)

EM, HM and XP pathways are universal in fungi

PK widespread among yeasts

ED – only for Tilletia caries and Caldariomycesfumago

Although EM and HM pathways lead through G3P to pyruvate but different metabolic functions.

EM uses NAD as electron acceptor.

HM leads to the reduction of NADP to NADPH.

There are other sources of reduced NADP for biosynthetic purposes besides HM pathway.

Fermentation

Regeneration of NAD by the transfer of electrons from NADH to an organic electron acceptor generated by the metabolism of the foodstuff.

In fungi this electron acceptor is pyruvate

Types of Fermentation

1. Alcoholic

2. Lactic acid

3. Mixed acid fermentation

Pyruvic acid as electron acceptor

ALCOHOLIC FERMENTATION

Pyruvate to ethanol and CO2

Saccharomyces

Aspergillus, Fusarium and Mucor are well known for this ability but obligate aerobes.

LACTIC ACID FERMENTATION

Found primarily in Chytridomycetes, Oomycetes and Zygomycetes

Rhizopus, a member of Zygomycete, carry out lactic acid fermentation together with alcoholic fermentation.

Mixed Acid Fermentation

Found in a small group of Chytridiomycetes

Similar to mixed acid fermentation of Enterobacteriaceae with acetate, lactate, formate, ethanol, methane, CO2 and H2 as end products.

RESPIRATION

In fungi is similar to that in other organisms.

3 interdependent processes

1. Citric acid cycle

2. Electron transport

3. Oxidative phosphorylation

Mitochondrion: center of respiration

TCA is a central hub of both catabolic and anabolic metabolism.

• ETC – 2nd critical process in respiration

ALTERNATIVE RESPIRATION

2 alternate pathways of electron transport that are distinct from the cytochrome path.

Differ from the cytochrome path in being insensitive to cyanide and sensitive to either salycil hydroxamate (SHAM) or azide.

• SHAM-sensitive pathway accepts electrons as the level of ubiquinol and transports them to O2 without proton transport

Without phosphorylation of ADP.

Azide-sensitive pathway also lack proton transport capability.

The alternative pathways are readily demonstrable when the normal pathway is blocked or limited.

ENERGY METABOLISM OF FUNGIGroup Name

Respiration Fermentation

Anaerobicgrowth

Fungi

Obligaterespirers

Yes No No Many yeasts and mostfilamentous fungi

Aerobicrespirers

Yes Anaerobic inpregrowncells

No A few yeasts andfilamentous fungi

Aerobicfermentors

Limited Aerobic andAnaerobic

No Schizosaccharomycespombe and otheryeasts

Facultativeaerobicfermentors

Limited Aerobic andAnaerobic

Facultative Saccharomycescerevisiae

Obligateanaerobes

Absent Anaerobic Obligate RumenChytridiomycetes

OTHER DEGRADATIVE PATHWAYS

Serve several functions:

1. Release of NH4 for reutilization

2. Provision of carbon metabolites utilizable as C and E sources

3. Detoxification of inhibitory compounds

Example: degradation of amino acids, purinesand pyrimidines.

GLUCONEOGENESIS

Required f o r growth on noncarbohydratecarbon sources

Involves substrates closely related to the EM pathway and requires the reversal of this process.

general property of fungi.