CH. 5+6: Metabolism and Growth

Oxidation

Loss of electrons or hydrogen ions; energy-releasing reaction used in glycolysis and the citric acid cycle

Reduction

Gain of electrons or hydrogen ions; always paired with oxidation in redox reactions

NAD+

Oxidized electron carrier; becomes NADH when reduced; carries electrons to the ETC to help produce ATP

FAD

Oxidized electron carrier; becomes FADH2 when reduced; produces less ATP than NADH because it enters the ETC at Complex II (skips Complex I)

Substrate-level phosphorylation

Direct transfer of a phosphate group from a substrate to ADP to form ATP; occurs in glycolysis and Krebs cycle

Oxidative phosphorylation

ATP production using the electron transport chain and chemiosmosis; produces most ATP in aerobic respiration

Glycolysis

Breaks glucose into 2 pyruvate; net gain of 2 ATP and 2 NADH; occurs in cytoplasm; produces G3P intermediate

Pyruvate oxidation (link reaction)

Converts pyruvate into acetyl-CoA; produces NADH and CO2; connects glycolysis to Krebs cycle

Krebs cycle

Oxidizes acetyl-CoA; produces 2 ATP, 6 NADH, 2 FADH2, and 4 CO2 per glucose

Electron transport chain (ETC)

Series of electron carriers that pass electrons to oxygen (final acceptor); drives proton pumping to create ATP

Chemiosmosis

Movement of H+ down its gradient through ATP synthase, producing ATP

Why FADH2 produces less ATP

FADH2 enters at Complex II, bypassing Complex I, resulting in fewer protons pumped and less ATP produced

Fermentation

Anaerobic process that regenerates NAD+ so glycolysis can continue; produces only 2 ATP

Lactic acid vs alcohol fermentation

Lactic acid fermentation produces lactic acid; alcohol fermentation produces ethanol and CO2 (yeast)

Why NAD+ recycling is important

Without NAD+, glycolysis stops and ATP production ceases in anaerobic conditions

Photoautotroph

Uses light for energy and CO2 for carbon (plants, algae)

Chemoheterotroph

Uses organic compounds for both energy and carbon (most pathogens, humans)

Prokaryote vs eukaryote ATP yield

Prokaryotes ~38 ATP; eukaryotes ~30–32 ATP due to mitochondrial transport costs

Psychrophile vs psychrotroph

Psychrophile prefers cold environments; psychrotroph can grow in refrigeration and spoil food

Mesophile

Grows best at moderate temperatures (~37°C); includes most human pathogens

Osmotic pressure (food preservation)

High salt or sugar creates hypertonic conditions, preventing microbial growth

Plasmolysis

Water leaves cell in hypertonic environment, causing shrinkage and loss of function

Halophile

Salt-loving organism; includes Staphylococcus species; grows on MSA

Obligate aerobe (thioglycollate)

Grows at top where oxygen is highest

Obligate anaerobe (thioglycollate)

Grows at bottom where oxygen is absent

Facultative anaerobe

Uses oxygen if available but can grow without it; grows mostly at top; has catalase and SOD

Aerotolerant anaerobe

Does not use oxygen but tolerates it; grows evenly throughout tube

Biofilm

Microbial community attached to a surface; resistant to antibiotics and immune response

EMB agar

Selective for Gram-negative bacteria; differentiates lactose fermenters; E. coli shows metallic green sheen

MacConkey agar

Selective for Gram-negative bacteria; lactose fermenters = pink colonies; non-lactose fermenters = colorless

MSA (mannitol salt agar)

Selects for halophiles; differentiates mannitol fermenters; S. aureus turns media yellow

Blood agar hemolysis

Alpha: partial (greenish); Beta: complete clearing; Gamma: no hemolysis

BSL1 vs BSL4

BSL1: low-risk organisms (E. coli); BSL4: highly dangerous pathogens (Ebola, smallpox)

Log phase

Rapid bacterial growth phase; cells are most metabolically active and most sensitive to antibiotics

Generation time

Time for population to double; varies by species (E. coli is fast, M. tuberculosis is slow)

CFU/mL formula

CFU/mL = (colonies ÷ volume plated) × dilution factor

Colorless colonies on MacConkey and EMB

Indicates non-lactose fermenter; possible pathogen requiring further testing

Meat preservation method

Add salt/sugar to create hypertonic environment causing plasmolysis and inhibiting growth

Thioglycollate bottom growth

Indicates obligate anaerobe

Clostridium culture

Use anaerobic conditions (thioglycollate medium or anaerobic chamber)

Antibiotics during log phase

Most effective because bacteria are actively dividing

Lake water testing

Use MPN (Most Probable Number) method to estimate coliform contamination