Chapter 7 - Microbial Metabolism

Metabolism

Pertains to all chemical reactions & physical workings of a cell

Anabolism

• Any process that results in synthesis of cell molecules & structures

• A building & bond-making process that forms larger macromolecules from smaller ones

• Requires the input of energy (Endergonic)

Catabolism

• Breaks the bonds of larger molecules into smaller molecules

• Releases energy (Exergonic)

Energy

• Stored in the bonds of ATP

• Energy will always be stored in chemical bonds

• Breaking bonds releases energy

Simplified model of metabolism

• Figure represents how catabolism and anabolism are linked together

• 1. Glucose catabolized (broken down) by respiration or fermentation (slowly)

  • Glycolysis & Krebs Cycle are processes that help break down

• 2. Precursor molecules are biproducts

• 3. Biproducts are used in anabolism (synthesis)

• **So, biproducts of catabolism are used for anabolism**

Redox reactions - oxidation vs. reduction

• Oxidation: loss of electrons

  • When a compound loses electrons, it is oxidized

• Reduction: gain of electrons

  • When a compound gains electrons, it is reduced

• Oxidation-reduction (redox) reactions are common in the cell & are indispensable to the required energy transformations

  • Oxidation & reduction happen simultaneously

Redox reactions

• Oxidoreductases: enzymes that remove electrons from one substance & add them to another

  • Their coenzyme carriers are nicotinamide adenine dinucleotide (NAD) & flavin adenine dinucleotide (FAD)

Reducing power

• Reducing power: electrons available in NADH & FADH₂

  • Produced when NAD & FAD gain an electron

  • Won’t allow the enzyme to function in this form

  • Produced during glycolysis or Kreb’s cycle

  • Produced during catabolism & needed in large quantities for anabolism

Reaction of respiration

Ends with Electron Transport Chain

3 main metabolism pathways (big picture)

• Pathways for bacteria to harvest energy from organic chemical compounds

• 1. Aerobic respiration: most amount of growth (fastest)

  • Yields 36-38 ATPs

  • Uses O₂ as electron acceptor

• 2. Anaerobic respiration: middle

  • Yields 2-36 ATPs

  • Uses non-O₂ (inorganic) compound as electron acceptor

  • Only in bacterial cells, NOT human cells

• 3. Fermentation: least amount of growth (slowest)

  • Yields 2 ATPs

  • Human cells do this instead of anaerobic respiration

**Know not only difference b/w aerobic & anaerobic, but also similarities**

Aerobic Respiration

• A series of reactions that convert glucose to CO₂ & allows the cell to recover significant amounts of energy

• Utilizes glycolysis, Krebs Cycle, & electron transport chain (ETC)

• Relies on free oxygen as the final electron & hydrogen accetpor

• Characteristic of many bacteria, fungi, protozoa, & animals

Anaerobic Respiration

• Used by strictly anaerobic organisms & others who are able to metabolize with or without oxygen (so eukaryotic cells can’t)

• Involves the same 3 pathways as aerobic respiration (glycolysis, Krebs Cycle, & ETC)

• Uses NO^-₃, SO₄^2-, CO₃^3- (Nitrate, Sulfate, Carbonate) & other oxidized inorganic compounds as terminal electron acceptors

Fermentation

• Incomplete oxidation of glucose

• Oxygen is not required

• Organic compounds are terminal electron acceptors

All 3 metabolic pathways begin with…

Glycolysis (identical in each pathway)

Glycolysis

• All 3 metabolic pathways start w/ this

• Turns glucose into 2 copies of pyruvic acid

  • Glucose is NOT completely broken down (b/c end product of glucose breakdown is CO₂)

• Total energy yield:

  • 2 ATPs, 2 NADHs, 2 Pyruvic Acids

Kreb’s Cycle - conversion of Pyruvic acid

• 2 Pyruvic acids produced at the end of glycolysis are converted to 2 Acetyl CoA

• It participates in additional chemical transformations while producing NADH & FADH₂

• Sometimes Krebs Cycle is called the “carbon and energy wheel”

Kreb’s Cycle - yield

• Total yield per 2 pyruvate (intermediate phase):

  • 2 CO₂, 2 NADH

• Total yield per 2 acetyl CoAs:

  • 4 CO₂, 2 ATPs, 6 NADHs, 2 FADHs

• Total yield of complete glucose breakdown:

  • 6 CO₂, 4 ATPs (from glycolysis & Kreb’s)