2.4.9(Poisons and medicinal drugs as inhibitors)

Give the 2 examples of metabolic poisons which act enzyme inhibitors

• Cyanide

• Snake venom

Describe how cyanide acts as an enzyme inhibitor and its effects

• Potassium cyanide is highly toxic, as it inhibits aerobic respiration. It also inhibits catalase:

  • When ingested, potassium cyanide is hydrolysed to produce hydrogen cyanide, a very toxic gas that can readily dissociate into H+ and CN- ions

  • The CN- ions bind irreversibly to an enzyme found in the mitochondria and inhibit the final stage of aerobic respiration

  • Because the final stage is inhibited, earlier stages cannot run and aerobic respiration stops

Describe how snake venom acts a enzyme inhibitor and its effects

• Venom from a green mamba snake contains chemical inhibitors that inhibit the enzyme acetylcholinesterase(AChE)

• This enzyme is important at neuromuscular synapses to break down the neurotransmitter, acetylcholine(ACh)

• If this enzyme is inhibited the ACh stays attached to the receptors and the muscle and keeps the muscle contracted

• This causes paralysis, as movement depends on muscle being able to contract and relax.

• If the muscles involved in breathing are paralysed, then the victim dies of suffocation

State 5 examples of medicinal drugs acting as inhibitors

• Aspirin

• ATPase inhibitor

• ACE inhibitors

• Protease

• Nucleoside reverse transcriptase inhibitors

Describe how aspirin acts as an enzyme inhibitor and the effects of aspirin

• Salicylic acid binds to enzymes that catalyse the formation of prostaglandins

• This it prevents the formation of prostaglandins that are cell-signalling molecules produced by the cell when tissues are infected for damaged

• Prostaglandins make nerve cells more sensitive to pain and increase swelling during inflammation

• Aspirin can also reduce the risk of blood clots forming in blood vessels which reduces the risk of stroke

• Children under 12 should not tale it as it ca damage their stomach lining

Describe how ATPase inhibitors act and their effect

• Chemicals(digitalis, digitoxin, digitalin, digoxin) from fox glove leaves are used a ATPase inhibitors

• They inhibit the sodium potassium pump in the cell membranes of the cardiac muscle cells and allow more calcium ions to enter the cells

• Calcium ions increase muscle contraction which strengthens the heart beat

• This therefore reduces the chance of heart failure and atria arrhythmia

Describe how ACE inhibitors act and their effects. How are they used

• They are medical drugs that inhibit the angiotensin converting enzyme(ACE), which normally operates in a metabolic pathway that ultimately increases your blood pressure

• They are used:

  • To lower blood pressure in patients with hypertension who cannot take beta-blockers

  • To treat heart failure - a low dose is given at first and the patient’s blood pressure in checked in case it falls too low

  • To minimise risk of a second heart attack or a stroke in patients who have suffered a myocardial infarction

Describe and explain what protease inhibitors are use for

• They are used treat some viral infections

• They prevent the replication of the virus particles within the host cells, by inhibiting protease enzymes so that the viral coats cannot be made

• These inhibitors often inhibit viral protease enzymes by competitive inhibition