Enzymes

Competitive Inhibition

competitive inhibition. Fake substrates competing with real substrates for the opportunity to bind at an active site (hence the name competitive) slows or stops enzyme function. Fake substrates look like real substrates to an enzyme\'s active site; they are, in essence, \'look-a-likes.
Competitive inhibitors bind the active site of an enzyme, preventing a real substrate from binding and a product from being formed.

Competitive Inhibition

Competitive inhibition can be overcome by addition of substrate, which increases an enzyme\'s chance of finding real substrate.

Competitive Inhibition EXAMPLES

Sildenafil
(Viagra)
Nitric Oxide (NO) binds receptors in the smooth muscle cells of the penis. This results in increased levels of cyclic guanosine monophosphate (cGMP) which increases vasodilation. An enzyme called PDE5 degrades cGMP. Sildenafil fits into the same active site of PDE5 as cGMP, thus competitively inhibiting PDE5 from working.

Competitive Inhibition

competitive inhibition. Fake substrates competing with real substrates for the opportunity to bind at an active site (hence the name competitive) slows or stops enzyme function. Fake substrates look like real substrates to an enzyme\'s active site; they are, in essence, \'look-a-likes.
Competitive inhibitors bind the active site of an enzyme, preventing a real substrate from binding and a product from being formed.

Competitive Inhibition

Competitive inhibition can be overcome by addition of substrate, which increases an enzyme\'s chance of finding real substrate.

Competitive Inhibition EXAMPLES

Sildenafil
(Viagra)
Nitric Oxide (NO) binds receptors in the smooth muscle cells of the penis. This results in increased levels of cyclic guanosine monophosphate (cGMP) which increases vasodilation. An enzyme called PDE5 degrades cGMP. Sildenafil fits into the same active site of PDE5 as cGMP, thus competitively inhibiting PDE5 from working.

Competitive Inhibition EXAMPLES

Cyanide
Cyanide acts as competitive inhibitor to the enzyme cytochrome c oxidase.
This prevents the electron transport chain (the last part of cellular respiration) from working, meaning that the cell can no longer produce ATP for energy.
Tissues that depend heavily on energy (the CNS and heart) are particularly affected.

Non-competitive Inhibitor

Non-competitive inhibitors dont attach to the active site of the enzyme but somewhere else on the enzyme. They alter the shape of the enzyme molecule in such a way that the active site changes its shape, making the active site no longer able to accommodate the substrate.

Non-competitive Inhibitor EXAMPLES

Strychnine
Is a colorless highly toxic alkaloid that causes muscular convulsions and eventual death through asphyxia.
Strychnine binds to glycine receptors preventing glycine (an inhibitory neurotransmitter) from binding. This causes motor neurons to continuously fire, and the victim has constant muscle contractions.
Commonly used in the baits of animal traps, these have been replaced recently with chemicals less toxic to humans. There is no known antidote.

Non-competitive Inhibitor EXAMPLES

Penicillin
Many antibiotics acts as allosteric inhibitors. Penicillin acts by binding to
the bacterial enzyme DD-transpeptidase. The bacteria uses this enzyme to catalyze the formation of peptidoglycan cross-links in its cell wall.
Without this enzyme it can no longer make new cross-links, all the while
continuing to make enzymes that hydrolyze (break-down) these links.
This will cause holes in the cell wall to form and eventually force the
bacteria to shed most if not all of its wall.

Bibliography

1- Inhibitions. (2013, August 14). Retrieved November 26, 2015, from http://www.biologyforlife.com/uploads/2/2/3/9/22392738/inhibitors.pdf
2-Turtle, E. (2012, October 6). Biology-Innovation. Retrieved November 26, 2015, from http://www.biology-innovation.co.uk/pages/biochemistry/enzymes/