Toxins Flashcards
Venomous definition
Capable of producing poison in a highly developed gland or group of cells and can deliver the toxin (i.e. barbs, beaks, fangs or modified teeth, harpoons, nematocysts (cnidaria)
Poisonous definition
Contains tissues that are toxic – no mechanism to deliver the poison.
Venom Delivery - Penetrant
Barb is ejected at prey (this is occurs via stimulation of the cnidocil)
This fills cell with water causing the cell to turn inside out which causes expulsion of the barb
These barbs can only be used once
Once used the nematocyst is sent back to the gastrovascular cavity for digestion and replaced by a nematoblast
Venom Delivery - Stenotele
Barb is released along with a long tube to wrap around prey:
The triggered capsule, which is ejected from the cell, discharges its tubular content (shaft, stylets and tubule) by a process of evagination.
In doing so the three joined stylets punch a hole into the cuticle of the prey through which the long evaginating tubule penetrates into the interior of the target
Cone Shells
fire expendable harpoon from proboscis
Snakes
around 20 proteins found in venom Viperidae: Long hollow fangs on a short maxillary bone, can be rotated independently (movable) Elapidae (i.e. cobras): Short, hollow, fixed fangs
Venoms
Contain proteins and peptides Defence: highly conserved - localised pain Predation: more variable/complex can be pro/anti coagulant developed in regard to specific diet highly metabolic to produce
Spiders and scorpions
may inject more venom with increased resistance
E.g. some scorpions have a pre-venom used for defence
If the threat persists after pre-venom injection, or the scorpion is hunting they will inject their more expensive/ metabolically costly proteinaceous and enzymatic venom
Widow Spiders
o Venom: Neurotoxic proteins Proteolytic enzymes (lead to oedema (fluid retention) and swelling) o Effects: Muscle pain, cramps, tremor Joint pain Headache and dizziness Oedema
Brown or Violin Spiders
o Venom: Sphingomyelinase D Phospholipase, hyaluronidase Protease Esterase, Ribonuclease Collagenase
o Effects:
Vascular damage and tissue necrosis
Lethality – intravascular hemolysis, thrombocytopenia
Hemoglobinuria leading to renal failure
Coagulation
Serpins are compounds that can inhibit serine proteases.
Some snake venoms cause coagulation, some cause anti-coagulation
Viperid species generally have hemotoxic and necrotizing effects causing tissue death (also some neurotoxins present in venom)
Elapid snakes tend to be predominantly neurotoxic effects
Snake Venom Metalloproteins
Affect blood clotting
Affect the permeability of blood molecules
Cleave parts of ECM (cleave integrin’s and cadherin’s) interfering whit how cells bind to each other
This leads to interruption of cell interaction and break down of blood vessels.
Haemostatic pressure is able to burst capillaries
Snake envenomation
Leads to inflammation and Oxidative stress
Viper envenomation tends to lead to tissue death
a - Neurotoxins
Elapids: cobra, Hydrophidae (sea snakes)
Inhibit nicotinic acetylcholine receptors at the neuromuscular junction
Alpha bungarotoxin (a-BTX) acts on the post synaptic cell leading to flaccid paralysis = can’t contract muscle (no breathing etc.)
Mongoose Resistance
Agile
Thick skinned
Resistance to a-neurotoxins (resistant to a-BTX)
This is a result of major substitutions in the ligand binding site (nAch receptors)
Mongoose nAchR (nicotine acetycholine receptor) does not bind a-BTX in vivo or in vitro
