MIC 102 Lecture 6-7 - Metabolism

Why are central metabolism pathways conserved among cellular organisms?

• Inherited from LUCA - common to all life

• Energy efficiency - extact ATP and reducing power

• Supplies biosynthetic precursors

• Enzymes are highly effective and evolved optimally

• Can be adapted for differnet environemnts

Describe the different type of “trophs” → energy (photo vs. auto) carbon (auto vs. hetero) electron (litho vs. organo)?

Energy Source

• photo- : light

• chemo-: chemical

Carbon Source

• auto-: CO₂

• hetero-: Organic compounds

Electron Source

• litho-: inorganic chemicals (ex: CH4, N2)

• organo-: organic compounds

Explain the role of entry and feeder pathways during fueling

Entry

• Refer to the mechanisms different fod molecules are broken down and enter central metabolic pathways

• initial breakdown

Feeder

• metabolic routes that convert specific molecules into intermediate of central metabolic pathways

• standardize carbon sources

How is NAD+ regenerated during metabolism and why a high concentration of NAD+ is important to a growing cell?

Ways NAD+ is regenerated

• Aerobic respiration - NADH donates e- to NADH dehydrogenase

• Anaerobic (Fermentation)

  • NADH donates e- to Pyruvate → lactate

  • NADH donates H to acetaldehyde → ethanol

Why is it important to a growing cell?

• Steps in Central metabolism (like Glycolysis and TCA) require NAD+ to accept e-s from molecules in these pathways

• Helps drive oxidation reactions to drive metabolic reactions forward

• Results in production of more precursors/metabolites

What is proton motive force (transmembrane gradient) and why is it important?

PMF

• electrochemical gradient caused by difference in pH and membrane potential

• Generated by → e- dlow through ETC complexes → energy from e-transfer used to pump H+ out of membrane → create proton gradient

Why is it important?

• Facilitates ATP synthesis during respiration

• Facilitate generation of PMF through ATP hydrolysis (can run in reverse)

• Convert light energy to chemical energy in photosynthesis

• Power solute transport (ex: lactose permease)

• Power flagellar rotation

• Maintain internal pH

Explain role of redox reactions, ETC, and transmembrane gradients in production of energy in aerobic and anaerobic respiration

Redox Reactions

• Involve the transfer of molecules, electron carriers like NADH donate electrons to ETC to drive chain of redox reactions for ATP production

ETC

• Consists of protein complexes that pass electrons from one to the next

• As electrons flow through chain, energy is released and used to pump protons across membrane

• Aerobic resp: final e- acceptor is Oxygen, Anaerobic resp: final e- acceptor varies (nitrate, sulfate, co2 , etc.)

Transmembrane gradient (PMF)

• result of H+ pumping from ETC, pump proton against gradient to cytoplasm (our outside membrane)

• protons then flow back down gradient through ATP synthase and give energy for ATP synthesis

Compare and Contrast the relative ATP yield, terminal electron acceptor and O2 requriement for fermentation, aerobic respiration, and anaerobic respiration

Fermentation

• net ATP yield: 2 ATP per Glc

• terminal electron acceptor: Pyruvate or acetaldehyde

• O2 requirement: no

Aerobic respiration

• net ATP yield: 30-32 ATP per Glc

• terminal electron acceptor: Oxygen

• O2 requirement: yes

Anaerobic respiration

• net ATP yield: 5-30 ATP per Glc

• terminal electron acceptor: inorganic molecules that aren’t O2

• O2 requirement: No

What would happen if a drug permeabilized the membrane (made it leaky) or block transfer of electrons between ETC enzymes?

If a drug did these things:

• it would inhibit the creation of a transmembrane gradient

  • if permeablized membrane → H+ freely diffuses across membrane against it’s → gradient can’t be used to make ATP

  • if block electron transfer → electron flow is halted, H+ will stop going across the membrane as a whole and stop being pumped, ATP synthase has no driving force

ATP and reductant (FADH2 adn NADH) produced in glycolysis, transition, reaction, and TCA cycle per glucose

Glycolysis

• ATP produced: 2

• NADH produced: 2

• FADH2 produced: 0

Transition reaction

• ATP produced: 0

• NADH produced: 2

• FADH2 produced: 0

TCA Cycle

• ATP produced: 2

• NADH produced: 6

• FADH2 produced: 2