Biology and Toxicology: Yeast Fermentation, Lead, Arsenic, and Nicotine

Fermentation

Anaerobic process where yeast converts sugar into ethanol and CO2 when oxygen is low

Yeast metabolism shift

When oxygen is abundant yeast switches from fermentation to aerobic respiration prioritizing cell growth

Aerobic respiration pathway

Pyruvate enters the TCA cycle and oxidative phosphorylation producing efficient ATP

Anaerobic metabolism in yeast

Pyruvate is reduced to ethanol during fermentation to regenerate NAD+

Pectin

Structural polysaccharide found in fruit cell walls

Pectin methylesterase effect in yeast

Enzyme activity can produce toxic byproducts

Acetaldehyde toxicity

Causes headaches nausea facial flushing and chronic liver damage including cirrhosis

Methanol toxicity mechanism

Toxicity occurs when methanol is metabolized to formaldehyde and formic acid

Formate toxicity

Inhibits cytochrome c oxidase stopping ATP production in mitochondria

Excitatory neurons

Depolarize membranes and promote signal propagation between neurons

Inhibitory neurons

Hyperpolarize membranes and reduce neuronal signaling

Ethanol effect on the brain

Causes dopamine surge producing temporary stimulation before sedative GABAergic effects dominate

Lead sulfide (PbS)

Natural lead ore also called galena

Lead(II) oxide (PbO)

Yellow or red oxide used in batteries and glass called litharge

Lead(IV) oxide (PbO2)

Brown compound used in lead-acid batteries

Lead(II

IV) oxide (Pb3O4), Red lead pigment and intermediate oxide

Lead carbonate (PbCO3)

White lead pigment historically used in paint

Lead acetate

"Sugar of lead" historically used in cosmetics and as a sweetener

Tetraethyl lead

Former gasoline additive containing lead

Zinc ion (Zn2+) role

Common enzyme cofactor required for many enzymatic reactions

Lead toxicity mechanism

Lead mimics and displaces Ca2+ Zn2+ and Fe2+ disrupting proteins enzymes and signaling

Lead biological role

The body has no biological requirement for lead

Lead effect on heme synthesis

Inhibits production of new red blood cells causing anemia

Lead renal toxicity

Accumulates in proximal tubular cells damaging mitochondria and impairing transporters

Lead mitochondrial toxicity

Disrupts mitochondrial membrane potential and electron transport chain reducing ATP

Scopulariopsis brevicaulis

Fungus that converts arsenic compounds into trimethylarsine gas

Gosio gas

Garlic smelling trimethylarsine gas produced from arsenic pigments by fungi

Arsenic toxicity mechanism As3+

Binds sulfhydryl groups inhibiting enzymes

Arsenic toxicity mechanism As5+

Mimics phosphate and disrupts ATP synthesis

Reactive oxygen species (ROS)

Damaging molecules generated during arsenic toxicity causing DNA damage and apoptosis

GRAS definition

Generally recognized as safe designation for substances used in food under intended conditions

GRAS testing limitation

Does not require long-term human trials

GRAS self-affirmation

Manufacturers can determine GRAS status themselves without mandatory FDA review

GRAS population safety evaluation

Safety based on population averages not specific vulnerable groups

GRAS meaning

Safe under intended conditions but not biologically inert

Non-monotonic dose response

Biological responses that vary unpredictably with dose especially for endocrine disruptors

Trans fat health effects

Raises LDL lowers HDL and increases inflammation and cardiovascular disease risk

Estradiol receptor affinity

Binds estrogen receptors with extremely high affinity

Bisphenol A (BPA)

Xenoestrogen that binds estrogen receptors with much lower affinity than estradiol

Southampton study

Found increased hyperactivity in children consuming artificial food colors and sodium benzoate

Alkaloids

Nitrogen containing bioactive compounds produced by plants and fungi often affecting the nervous system

Alkaloid solubility property

Charged form is water soluble while neutral form is lipid soluble

Alkaloid absorption

High pH in the small intestine makes alkaloids neutral allowing easier absorption

Alkaloid receptor binding

Lower pH in blood promotes charged form that binds receptors and ion channels

Nicotine molecular mimicry

Mimics acetylcholine allowing binding to nicotinic acetylcholine receptors

Nicotine low dose effect

Stimulates receptors increasing alertness heart rate and blood pressure

Nicotine moderate dose effect

Causes sustained receptor activation leading to tremors and nausea

Nicotine high dose effect

Causes depolarization blockade leading to paralysis and respiratory failure

Nicotine chronic exposure

Causes receptor upregulation leading to addiction

Strychnine mechanism

Blocks glycine receptors preventing inhibitory chloride influx

Strychnine toxicity effects

Causes hyperexcitable motor neurons violent spasms and rigid muscle extension

Protein toxins vs non protein toxins

Differ in structure immune response and biochemical behavior

Ricin entry mechanism

B chain binds galactose receptors allowing endocytosis into the cell

Ricin toxic action

A chain inactivates ribosomes preventing protein synthesis

Cyanide toxicity mechanism

Rapidly inhibits cellular respiration by blocking cytochrome c oxidase

Cyanide absorption

Small lipophilic molecules rapidly cross membranes and enter bloodstream

Botulinum toxin mechanism

Cleaves SNARE proteins preventing acetylcholine release at neuromuscular junction

Botulinum toxin effect

Prevents muscle contraction leading to paralysis

Batrachotoxin mechanism

Keeps voltage gated sodium channels permanently open

Batrachotoxin physiological effect

Persistent depolarization causing paralysis and cardiac arrhythmias

Autointoxication

When an organism is harmed by its own toxin or venom

Weed definition

Any plant growing where it is not wanted

Noxious plant definition

Plant legally classified as harmful to agriculture or ecosystems

Toxic plant definition

Plant producing compounds that can cause illness injury or death

Atropine and scopolamine action

Competitive antagonists at muscarinic acetylcholine receptors

Scopolamine toxicity feature

High lipid solubility increases brain penetration

Atropine overdose reversal

Can be counteracted by increasing acetylcholine levels

Coniine mechanism

Acts as both agonist and antagonist at nicotinic acetylcholine receptors

Urushiol chemical reaction

Oxidizes to reactive quinone that binds skin proteins

Urushiol immune response

Hapten protein complexes trigger immune recognition

Langerhans cell role

Detect modified proteins and present them to immune system in lymph nodes

Type IV hypersensitivity reaction

Delayed T cell mediated immune response causing poison ivy dermatitis

Th1 cell role in urushiol dermatitis

Release inflammatory cytokines causing swelling and redness

CD8 cytotoxic T cell role

Kill keratinocytes causing blistering and tissue damage

Alpha amanitin mechanism

Inhibits RNA polymerase II blocking mRNA synthesis

Alpha amanitin vulnerable tissues

Rapidly dividing cells such as liver GI epithelium and kidneys

RNA polymerase II importance

Essential enzyme required to produce protein coding mRNA

Viruses using RNA polymerase II

Herpes HPV Hepatitis B and HIV hijack host Pol II for gene transcription