MYCO 3.1B Fungal Energetics & Metabolism

T/F: Fungal energetics focus on how fungi produce energy (i.e., biochemical reactions involved), while fungal metabolism pertains to how fungi synthesize substances essential for their growth & survival

TRUE

_ are the central reactions in fungal metabolism

• Glycolysis (Embden-Myerhoff-Parnas pathway)

• Krebs cycle (Citric Acid cycle)

T/F: Aerobic respiration is a process that reduces oxidized organic compounds in a controlled manner

FALSE

Aerobic respiration is a process that oxidizes reduced organic compounds in a controlled manner;

C6H12O6 (reduced) → (oxidized form)

T/F: There are many pathways that can branch out from or go into glycolysis

TRUE

Differentiate substrate-level vs. oxidative phosphorylation

• Substrate-level involves direct transfer of phosphate group from a high-energy substrate to ADP, forming ATP

• Oxidative uses electron transport chain to generate proton gradient that drives ATP synthesis of ATP synthase

T/F: Both glycolysis and citric acid cycle involves substrate-level phosphorylation, while oxidative phosphorylation is only observed in electron transport chain

TRUE

Oxidizing substances imply _ and thus _

breaking down its bonds and thus releasing energy, prompting creation of reduced temporary energy carriers, e.g., NADH, FADH₂

Glycolytic pathway is very fundamental in both _

energy production and biosynthesis

_ releases stored energy in organic molecules for cellular function; hence, a catabolic reaction

Aerobic respiration

_ is the process oxidizing reduced organic compounds in a controlled manner; during this process, free energy is released and stored in a compound called ATP

Aerobic respiration

During respiration, free energy is released and transiently stored in a compound called _

ATP

Enumerate 5 pathways involved in aerobic respiration (oxidizes reduced organic molecules to release free energy for cellular function)

1. Glycolysis = Glucose (6C) → Pyruvate (3C) [cytosol]

2. Pyruvate decarboxylation / oxidation = Pyruvate (3C) → Acetyl-CoA (2C) [MT matrix]

3. Citric acid cycle = to generate electron carriers (NADH, FADH₂) that will drive ATP synthesis via proton gradient during ETC

4. Electron transport chain = use movements of electrons across carriers to pump H+ across membrane and generate proton gradient that will drive ATP synthesis via ATP synthase

5. Oxidative phosphorylation = use electrons to generate ATP

In glycolysis, sucrose (glucose + fructose) may be used to end up with more energy because they produce _

pyruvate + malate

Describe reactants & products of glycolysis (EMP); TLDR glycolysis

• Reactants = Glucose (6C) + 2NAD⁺ + 2 Pi + 2 ADP

• Products = 2 pyruvate (3C) + 2 NADH + 2 ATP (net) + 2 H2O + 2 H⁺ + heat

*4 ATP in total

Glycolysis

(1) Glucose → G6P = - 1 ATP

G6P → F6P

F6P → F-1,6-BP = - 1 ATP

(2) F-1,6-BP → G3P, DHAP

(3) G3P (+Pi) → 1,3-BPG = + 2 NADH

1,3-BPG (-Pi) → 3-PG = + 2 ATP

3-PG → 2-PG

2-PG → PEP = + 2H2O

PEP (-Pi) → Pyruvate = + 2ATP

During _, free energy is released and transiently stored in a compound called ATP

respiration

In glycolysis, glucose may have come from other sources—_ can pass through biochemical pathways (gluconeogenesis) that ultimately make glucose

protein & fat

In glycolysis, _ (glucose + fructose) may be used to end up with more energy because they produce pyruvate + malate

sucrose

Before entering _, the pyruvate from glycolysis must first be decarboxylated to yield _

• Krebs cycle (TCA)

• Acetyl CoA (2C)

ETC is needed to generate _ needed for chemiosmotic coupling

proton gradient

Explain the process of pyruvate decarboxylation link reaction

1. Pyruvate is first transported from cytosol → MT matrix via pyruvate translocase

2. A carboxyl group (1C) is removed from pyruvate (3C) to make 2C derivative; hence the term “decarboxylation”

   1. -COOH is released as CO2

3. Decarboxylated 2C intermediate is then oxidized, with lost e- picked up by NAD+, forming NADH

4. Oxidized 2C is now an acetyl group, which will be joined to a Coenzyme A group (derivative from Vit B5) to form Acetyl-CoA

The complete oxidation of Acetyl-CoA reduces _ in a process called the citric acid cycle (TCA)

NAD+ & FAD+ → NADH & FADH₂

Per completely oxidized Acetyl-CoA, _ are produced

• 3 NADH

• 1 FADH2

• 1 ATP

Explain citric acid cycle (TCA/Krebs)

Acetyl-CoA (2C) condenses with oxaloacetate (OAA, 4C) and undergoes series of conversions that regenerates OAA & produces reduced temporary energy carriers: 3 NADH, 1 FADH2, 1 ATP per completely oxidized Acetyl-CoA

• A-CoA + OAA → 6C citrate

• 6C citrate → 6C isocitrate

• 6C isocitrate → 5C a-keto

  • + CO2

  • + NADH

• 5C a-keto → 4C succinyl CoA

  • + CO2

  • + NADH

• 4C succinyl CoA → 4C succinate

  • + 1 ATP

• 4C succinate → 4C fumarate

  • + 1 FADH2

• 4C fumarate → 4C malate

  • + NADH

• 4C malate → 4C OAA

• 4C OAA + 2C A-CoA → 6C citrate

In the beginning of TCA (Krebs), Acetyl-CoA (2C) is condensed with _ and undergoes series of conversions that regenerates _ but produces reduced temporary energy carriers, including 3 NADH, 1 FADH2, 1 ATP, per completely oxidized Acetyl-CoA

oxaloacetate (OAA)

Overall reaction of aerobic respiration suggests that CO2 is produced as a waste, and this is evident in _ stages

Pyruvate decarboxylation, TCA

_ is needed to generate proton gradient for chemiosmotic coupling

Electron Transport Chain (ETC)

Explain chemiosmotic coupling

*Reduced temporary energy carriers + ATP produced from glycolysis & TCA then participate here

1. [ETC] Electron transport (transport of electrons from 1 carrier to another) drives the pumps to pump protons across the membrane, allowing protons to establish an electrochemical H+ gradient

   1. NADH is oxidized, releasing electron that goes into ETC that allows H+ to be pumped from matrix to IMS

2. [Oxidative phosphorylation] Proton gradient is harnessed by ATP synthase to make ATP, as H+ re-enters the MT matrix

Cells use _ to mill energy from an electron donated by either NADH or FADH2 to move H+ from the MT matrix into intermembrane space (IMS)

electron transport chain

Hydrogen cannot enter MT matrix except through _

ATP synthase

H+ accumulation in IMS creates an electrochemical gradient due to 2 things, including _

cocha

• H+ concentration difference in IMS & matrix, thus a pH change (lower pH in IMS than matrix)

• Charge difference = IMS is more positive

Explain 1st step of chemiosmotic coupling: ETC

NADH+ (reduced) → (oxidized) high energy e- + H⁺ + NAD+ (re-used)

• High energy e- travel thru ETC complexes, driving active pumping of H+ from matrix into IMS

• This results in H+ accumulation in IMS that creates an electrochemical gradient

  • Concentration difference → change in pH (low outside)

  • Charge difference → IMS more electropositive

• H+ goes back into MT matrix via ATP synthase (passive transport)

• NAD⁺ for reuse in glycolysis and the citric acid cycle

_ functions via rotational catalysis through the binding change mechanism that drives ATP synthesis

ATP synthase

ATP synthase functions via _ through _ that drives ATP synthesis

• Rotational catalysis

• Binding change mechanism (cycling between loose ADP, tight ATP, open or empty conformation)

T/F: Hydrogen cannot enter the MT matrix except through ATP synthase

TRUE

T/F: F1 of ATP synthase has 3 chemically similar but conformationally distinct alpha, beta protomers—each of which has 1 catalytic site for protein synthesis (L,T,O)

FALSE

F1 of ATP synthase has 3 chemically identical but conformationally distinct alpha, beta protomers—each of which has 1 catalytic site for protein synthesis (L,T,O)

Each protomer (a or b) (within rotor) has 1 catalytic site, either _

• Loose conformation = binds ligands loosely

• Tight conformation = binds ligands tightly, catalytically active

• Open / empty conformation = has very low affinity for substrates/products

Explain binding change mechanism that explains rotational catalysis of ATP

1. H+ accumulates in IMS due to ETC pumping H+ out into IMS

2. H+ cannot enter MT matrix except through ATP synthase

3. ATP synthase functions via rotational catalysis through binding change mechanism (cycling between L,T,O states) that drive ATP synthesis, such that

4. As H+ passes through ATP synthase, gamma subunit induces conformational changes in alpha & beta subunits, promoting the ff:

   1. Initially = ATP in T conformation, then ADP+Pi binding in L conformation

   2. Addition of energy causes L site to become T, O to L, T to O

   3. This causes ADP+PI in T, ATP in O, causing its release, with H2O as byproduct of hydrolysis

   4. New ATP then spontaneously forms in the new T site

   5. After 2 such sequences, enzyme returns to its initial state

T/F: ATP synthase directly uses the energy of proton flow to synthesize ATP, rather than to induce conformational changes that drive ATP synthesis

FALSE

Proton flow induces conformational changes that allow ATP synthesis, rather than directly providing energy to form the bond

T/F: The release of ATP from ATP synthase requires energy input from the proton gradient

TRUE

The energy from proton flow is required to induce the conformational change (from T to O) that allows ATP release

T/F: ATP is synthesized in the Loose (L) conformation of ATP synthase

FALSE

ATP is synthesized in the Tight (T) conformation of ATP synthase

T/F: A single full rotation of the γ subunit of ATP synthase results in the synthesis and release of three ATP molecules

TRUE

The γ subunit rotates in 120° steps, and a full 360° rotation cycles through three catalytic sites, each producing one ATP

*120deg = 1 ATP in 1 site
Full rotatio 360 deg = 1 ATP in each of 3 sites = 3 ATP

The complete oxidation of 1 glucose molecules produces an equivalent of _

36 - 38 ATP

1 NADH forms _ ATP, while 1 FADH2 forms _ ATP

• NADH = 3 ATP

• FADH2 = 2 ATP

Explain energy generation in aerobic respiration

T/F: The proximity of ADP + Pi is what causes production of ATP

TRUE

The general conversion of ATP produced by NADH = 3, FADH = 2, but in reality, it is actually close to _

NADH = 2.5/molecule, FADH2 = 1.5/molecule

T/F: Fungi can perform fermentations when O2 is not available as electron donor

FALSE

Fungi can perform fermentations when O2 is not available as electron acceptor

Explain lactic acid & ethanol fermentation pathways

• Lactic acid fermentation

  • Pyruvate from glycolysis is directly converted to (reduced to) lactate, using NADH and thus oxidizing this back to NAD+ (to be used for another round of glycolysis)

  • The whole pathway yields much less overall energy than complete oxidation

• Ethanol fermentation

  • Pyruvate is converted to (oxidized to) acetaldehyde, releasing CO2

  • Acetaldehyde is reduced to ethanol by oxidizing NADH in the process, thus regenerating NAD+ necessary for glycosis to continue

• Goal: to regenerate NAD+ so glycosis can continue to produce ATP under anaerobic conditions

T/F: Ethanol fermentation produces more ATP per glucose molecule than lactic acid fermentation

FALSE

Both only produce 2 ATP per glucose via glycolysis

T/F: In ethanol fermentation, NADH is oxidized to NAD⁺ during the conversion of pyruvate to acetaldehyde

FALSE

In ethanol fermentation, NADH is oxidized to NAD⁺ during the conversion/reduction of acetaldehyde to ethanol

T/F: Only ethanol fermentation releases CO2, making it the only fermentation pathway that contributes to bread rising

TRUE

Lactic acid fermentation does not release CO₂, whereas ethanol fermentation does—this is why yeast makes bread rise

T/F: The production of ethanol and CO2 in yeast fermentation is necessary for regenerating ATP

FALSE

The fermentation process itself does not generate ATP; ATP is only produced during glycolysis

T/F: Lactic acid fermentation occurs in fungi and some bacteria, but never in human cells

FALSE

human muscle cells undergo lactic acid fermentation during anaerobic conditions like intense exercise

T/F: Fungi evolved to do fermentation despite yielding more ATP via aerobic respiration to survive under anaerobic conditions

TRUE

_ is the starting molecule for Pentose Phosphate Pathway

G6P

Explain Pentose Phosphate Pathway

*Functions for both energy production & biosynthesis

• Under oxidative phase

  • G6P → 6-phosphogluconate

    • NADP+ → NADPH, which is then used to regenerate glutathione back to its active form to neutralize ROS, e.g., H2O2

    • NADPH → 2 GSH to GSSG, which converts H2O2 → H2O

  • 6-phosphoglucanate → Ribulose-5-phosphate, producing another NADPH, releasing CO2

  • Ribu-5-P → Ribose-5-phosphate, producing sugar backbones for synthesis of nucleotides, coenzymes, DNA, RNA

• Under nonoxidative phase

  • Ribulose-5-P can be converted back to G3P, F6P, which can reenter EMP and produce other types of sugars to be used, for instance, for cell wall synthesis

T/F: Under nonoxidative phase of PPP, ribose-5-phosphate can be converted to G3P or F6P to re-enter EMP

FALSE

Under nonoxidative phase of PPP, ribulose-5-phosphate can be converted to G3P or F6P to re-enter EMP for production of other sugar types

T/F: In PPP, ribulose-5-phosphate can be used as sugar backbones for producing nucleotides, coenzymes, DNA, RNA

FALSE

In PPP, ribose-5-phosphate can be used as sugar backbones for producing nucleotides, coenzymes, DNA, RNA

T/F: In Pentose Phosphate Pathway, oxidative phase is irreversible, nonoxidative is reversible

TRUE

T/F: In Pentose Phosphate Pathway, the nonoxidative phase does not regenerate NADPH but allows sugar rearrangements

TRUE

In PPP, _ produced from converting G6P to 6-phosphogluconate reduces glutathione (GSSG) back to its active form (GSH)

NADPH

_ detoxifies ROS like H2O2 by converting it to H2O, preventing oxidative damage

Glutathione (GSH)

T/F: NADPH generated from the PPP is essential for neutralizing reactive oxygen species (ROS) by maintaining glutathione in its reduced form (GSH)

TRUE

T/F: A deficiency in the PPP would have the greatest impact on cells that experience high oxidative stress, such as red blood cells

TRUE

Red blood cells lack mitochondria and depend on NADPH from the PPP to regenerate glutathione and prevent oxidative damage

T/F: Inhibition of glucose-6-phosphate dehydrogenase (G6PD), the first enzyme in the PPP, would impair a cell’s ability to synthesize nucleotides and manage oxidative stress

TRUE

G6PD deficiency reduces NADPH levels, making cells vulnerable to oxidative stress and limiting their ability to produce ribose-5-phosphate for nucleotide synthesis

T/F: In PPP, ribulose-5-phosphate can regenerate G6P under oxidative conditions but indirectly via glycolytic intermediates, e.g., G3P, F6P

FALSE

In PPP, ribulose-5-phosphate can regenerate G6P under nonoxidative conditions but indirectly via glycolytic intermediates, e.g., G3P, F6P

_ refers to the metabolic process where fatty acids are broken down in the mitochondria into acetyl-CoA, NADH, FADH2, which can then enter TCA and ETC to produce ATP

Beta-oxidation

T/F: Both lactic acid and ethanol fermentation occur in cytosol

TRUE

The fatty acyl CoA is shortened by _ carbons per 1 beta oxidation cycle

2

Beta oxidation cycle of fatty acids continue until _

fatty acid is completely degraded

Explain beta-oxidation of fatty acids

• [cytosol] Glu → Pyruvate (glycolysis)

• Pyru → [mito] TCA → citrate

  • Citrate is pumped out to cytosol

  • Citrate → acetyl-CoA → Palmitoyl-ACP (precursor for first FA)

  • → Palmitic acid (C16 FA), which then enters ER, where no. of carbons can be changed (shortened/lengthened), producing triglycerides + long chain fatty acids

• TAG + LCFA enter mitochondria, undergoing beta-oxidation cycle

  • Per beta-oxi cycle, fatty acyl CoA is shortened by 2 carbons

  • e.g., 4C fatty acyl CoA, after producing 1 acetyl CoA (which is 2 carbon), reenters beta-oxi cycle as 2C fatty acyl CoA

    • NADH, FADH2 is produced in the process

  • Cycle repeats until the entire fatty acyl CoA is completely degraded

Triglycerides and long-chain FAs are sent to _ for beta-oxidation

mitochondria

Fatty acids are first activated to _ in the mitochondria by acyl-CoA synthetase before entering beta-oxidation

fatty acyl-CoA

During beta-oxidation of fatty acids, _ are the energy carriers produced

NADH + FADH2

T/F: Each round of β-oxidation shortens a fatty acid chain by one carbon, producing Acetyl-CoA

FALSE

Each round of β-oxidation shortens a fatty acid chain by two carbon, producing Acetyl-CoA

T/F: Fungal β-oxidation is essential for generating Acetyl-CoA, which can enter both the TCA cycle and gluconeogenesis

TRUE

T/F: The first step of β-oxidation involves the activation of fatty acids in the mitochondria using ATP

TRUE

Fatty acids are activated to fatty acyl-CoA by acyl-CoA synthetase before entering β-oxidation

T/F: Fatty acid synthesis and β-oxidation occur in the same cellular compartment to ensure efficient regulation

FALSE

• FA synthesis = cytosol + ER

• Beta-oxidation = mitochondria

T/F: If the fungal cell needs to generate energy, then it’s most likely not going to export citrate, but if it needs to extend its hypha, then it will need to export some citrate to create phospholipids of plasma membrane

TRUE

Describe 2 circumstances where citrate would need to be exported out of mitochondria for fatty acid synthesis

• If there is an absolute need to synthesize some kind of lipids, or

• If there is an excess of materials and would want to store excess energy in the form of fat

_ are critical for fungi, as they use these for wns walls, nucleotides, and storage compounds; produced using 2 carbon precursors (acetate)

Sugars

Sugars are critical for fungi, as they use these as for _; produced using _

• wns walls, nucleotides, storage compounds

• 2-carbon precursors → acetate

_ creates glucose via glyoxylate cycle

Gluconeogenesis

• _ is a shortcut to Krebs, where isocitrate is converted to glyoxylate (2C), which, in turn, is converted to malate, then to oxaloacetate

• OAA can be converted to PEP, which can then be used to create glucose via reverse glycolysis

• By adding CO2 + pyruvate → OAA

Glyoxylate cycle

_ can be converted to PEP, which can then be used to create glucose via reverse glycolysis

OAA (oxaloacetate)

In glyoxylate cycle, OAA can be made by _

adding CO2 to pyruvate

T/F: Glyoxylate cycle is a sugar synthesis pathway

TRUE

(4C) OAA produced from shortcut glyoxylate cycle can be converted back to (3C) pyruvate → (6C) glucose

Explain the importance of glyoxylate cycle in fungi

• Fungi use glyoxylate pathway to grow on acetate or fatty acids by bypassing the CO2-releasing steps of TCA, thus allowing carbon conservation for biosynthesis

• It allows fungi to generate sugar from FA when carbohydrates are not available in their environment

• Mammals lack this pathway, hence we cannot convert fats into glucose

Explain glyoxylate cycle

• Acetyl CoA → TCA

  • 6C citrate → 6C isocitrate

  • 6C isocitrate → 2C glyoxylate + 4C succinate (biosynthesis)

  • 2C glyoxylate + 2C acetyl CoA → 4C malate

  • 4C malate → 4C OAA

• 4C OAA can be used to produce glucose via reverse glycolysis

  • 4C OAA → (-CO2) 3C Pyruvate

  • 3C pyruvate → 6C glucose

• Or 4C OAA can be made by CO2 + (3C) pyruvate

During glyoxylate cycle, gluconeogenesis (glucose production) may occur by removing _ to OAA, producing either pyruvate or PEP

1 CO2

T/F: Glyoxylate is a four-carbon intermediate produced from isocitrate

FALSE

Glyoxylate is a two-carbon (2C) compound, while the other product, succinate, is four-carbon (4C)

T/F: Fungi and bacteria rely on the glyoxylate cycle to survive in carbon-poor environments

TRUE

It allows them to use acetate or fatty acids as carbon sources

Fungi derive both chitin and chitosan from _

modification of glucose molecules

Explain composition/structure of chitin & chitosan

• Chitin = 2 N-acetylglucosamine (NH=O)

• Chitosan = 1 N-acetylglucosamine + 1 Glucosamine (NH2)

Explain chitin & chitosan biosynthesis

• Glycogen → Glu-1-P → Glu-6-P

• Trehalose → Glu → Glu-6-P

  • Glu-6-Pho → F6P → Glucosamine-6-P, converting glutamine → glutamic acid

  • Glucosamine-6-P → (Acetyl-CoA > CoA) N-acetylglucosamine-6-P

    • Glucosamine = precursor to N-acetylglucosamine

  • N-acetylglucosamine-6-P → N-a-1-p

  • Chitin (2 N-acetylglucosamine)

  • Chitosan (1 N-acetyl + 1 glucosamine)

Explain connected paths to EMP (Glycosis) & TCA

fpbg cl

• Fermentation = to regenerate NAD+ for ATP production

  • Lactose & ethanol

• Pentose Phosphate Pathway = regenerate active GSH for neutralizing ROS; produce sugar backbones for nucleotides, coenzymes, DNA, RNA; regenerate G3P, F6P that can re-enter EMP

  • Biosynthesis + energy production

• Beta-oxidation = FAs converted into acetyl CoA for energy

• Glyoxylation = use weird FAs/acetate to produce sugars (OAA > pyruvate > PEP > glucose)

  • Biosynthesis + energy production

• Chitin & chitosan biosynthesis

• Lysine biosynthesis

T/F: Chitosan is a deacetylated version of chitin with variable fraction of glucosamine residues

TRUE

Fungi synthesize the essential AA lysine via _

alpha-aminoadipate (AAA) pathway

_ are needed by fungi to synthesize proteins required for mcps mycelial growth, conidiation, stress resistance, and predacious abilities (e.g., nematode-trapping fungi)

Lysine

Lysine is needed by fungi to synthesize many proteins required for _

mcps

• Mycelial growth

• Conidiation

• Stress

• Predacious abilities (e.g., nematode-trapping fungi)