BIOL115 - Lecture 9

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  • Created by: Katherine
  • Created on: 16-05-16 09:21
Is the activity of enzymes increase or reduced in the presence of certain other molecules or ions?
It is reduced
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What are inhibitors used for?
They are important in the regulation of cellular activity
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Generally, what are enzymes?
Common drugs and toxins.
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What can inhibitors be used for?
To investigate enzyme mechanisms
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What is an irreversible enzyme inhibitor?
It is an inhibitor that binds permanently to enzyme. It usually mimics substrate to bind to catalytic centre.
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What does the inhibitor do the the substrate?
It becomes covalently attached to catalytic group during catalysis. Ths step is irreversible for this type of inhibitor.
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What is a suicide inhibitor?
irreversible form of enzyme inhibition that occurs when an enzyme binds a substrate analogue and forms an irreversible complex with it through a covalent bond during the "normal" catalysis reaction.
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What type of inhibitors are reversible?
Competitive, non competitive and uncompetitive
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Where do competitive inhibitors bind?
On the active site
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Where do non competitive inhibitors bind?
Non active site
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Where do uncompetitie inhibitors bind?
ES complex
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What happens when uncompetitive inhibitors bind?
It changes the orientation of the active site or hinders the release of the active site.
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What is an example of an irreversible inhibitor?
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When was aspirin first marketed?
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What does Aspirin do?
It blocks prostaglandin synthesis
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What is the enzyme involved in prostaglandin synthesis>
Prostaglandin H2 synthase - aka cyclooxygenase.
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What is COX1?
It is an isoform of cyclooxygenase: It is widespread and constitutivie
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What is COX2?
It is an isoform of cyclooxygenase: Is is released during the inflammatory response.
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What is the mechanisms of action of aspirin?
It causes COX to become inactive
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What are the pharmacological uses of aspirin?
Low dose - prevention of thrombosis. Normal dose - anti-nflammatory and pain killer.
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How does low dose aspirin prevent thrombosis?
It inhibits COX1 in blood platelets, preventing prostaglandin/ thromboxane mediated aggregation.
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How does aspirin act as a pain killer and ant inflammatory?
It inhibits COX1 and COX2 in most tissues, reducing inflammation and pain response and fever.
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What are the side effects of aspirin?
Stomach ulcers - Prostaglandns prevent acid secreation (COX1)
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Why can you have paracetamol and aspirin at the same time?
Because paracetamol doesn't have an anti inflammatory response.
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Why do non competitive enzymes not bind in the active site?
They bind outside the active site so the active site can be utilised in the correct way.
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What are competitive inhibitors typically?
Non metabolisable substrate analogues.
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What does this mean?
It means that enzymes can bind either the substrate or the inhibitor.
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What does this result in?
Simple cometition for active site.
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How can inhibition be overcome?
By adding more substrate
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Potenty of inhibitor releated to affinity for active site compared to substrate.
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Give an example of a competitive inhibitor:
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What dos inhibitoion of DHFR do?
It prevents cell division.
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What is methotrexate?
It is a major chemotherapy drug for treatment of cancers of the breast, bladder, head , neck ect.
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Is inhibition of DHFR effective against cancer?
It is effective, but it is not specific to cancer cells - it affects all cells.
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What is another DHFR inhibitor?
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What is Pyrimethamine?
It only affectts protozoans, not mammalian cells.
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Give an example of an irreversible inhibitor:
5 Fluorouracil
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What is 5 Fluorouracil?
It is a chemotherapy drug that blocks DNA synthesis by inhibiting the production of pyrimidnes and puries.
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When competitive inhibitors are present, will Vmax be reached?
Yes, for each inhibitor at high S.
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Will Km be higher or lower in the presence of inhibitors?
It will be higher.
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What would a lineweaver burk plot look like with a competitive inhibitor?
The lines would cross at the same position (intercept)
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Is non competitive inhibition reversible or irreversible?
It is reversible
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Can non competitive inhibition be overcome by the addition of more substrate?
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What does the non competitive inhibition do?
It changes the rate of catalysis, i.e. the turnover number.
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When does non competitive inhibition occur?
When inhibitor binds at a site away from the active site, can bind eithe E or ES.
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When does uncompetitive inhibition occur?
It occurs when an inhibitor binds ES complex, but not free enzyme.
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What is an example of uncompetitive inhibition?
Lithium as a a drug treatment for manic depression. It is an inhibitor of myo-inositol monophosphatase.
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What would the lineweaver burk plot of an uncompetitive inhibitor look like?
There would be no difference to the slop of the graph. Km would be increased and Vmax reduced by the same factor.
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PDE 5 of inhibitor X was renames?
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What are inhibitors used for?


They are important in the regulation of cellular activity

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Generally, what are enzymes?


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What is an irreversible enzyme inhibitor?


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