MECHANISM OF DRUG ACTION

Question 1

What is ligand?

Answer 1

Ligand is the substance that binds to a target and alter the 3D conformation.

Question 2

List the type of ligands and give examples for each type.

Answer 2

1. Exogenous ligand
   - toxins, poisons, drug
2. Endogenous ligand
   - hormones, mediators, cytokines.

Question 3

What is affinity?

Answer 3

Affinity is the ability of a ligand to bind a target.

Question 4

What is selectivity?

Answer 4

Selectivity is the ability of a ligand to bind to a specific target.

Question 5

1 ligand can bind to many receptors. It is considered as …..

Answer 5

non selective drug

Question 6

What is receptor?

Answer 6

Receptor is the protein that receive and transduce signals and produce different tissue response.

Question 7

What is efficacy?

Answer 7

Efficacy is the ability to activate the receptors.

Question 8

What is full agonist?

Answer 8

Full agonist is the binding to a receptor and produce a maximal effect

Question 9

What is antagonist?

Answer 9

Antagonist is the binding to a receptor and produce no effect at all, In other words, it prevents the activation of receptor by the agonist.

Question 10

What is partial agonist?

Answer 10

Partial agonist is the binding to a receptor and produce submaximal effect which is less than 100%.

Question 11

What is inverse agonist?

Answer 11

Inverse agonist is the binding of a receptor and produce an opposite effect than the agonist effect.

Question 12

Describe how the G protein works (Gs. Gi, Gq)

Answer 12

• Gs stimulate adenyl cyclase.
• This causes the ATP to be converted to cAMP.
• The conversion to cAMP causes the protein kinase A to be activated.
• The activation of protein kinase A causes the Ca2+ increase.
• While, Gi inhibit the adenyl cyclase.
• This causes the amount of ATP to be converted to cAMP to be decreased.
• Hence the protein kinase A cannot be activated.
• Thus, the amount of Ca2+ is reduced.
• However, the amount of K+ is in high amount.
• Thus membrane hyperpolarisation occur.
• In Gq will activate the phospholipase C.
• This causes the cleave of PIP2 to IP3 and DAG.
• IP3 will causes high amount of Ca2+ produced.
• While, DAG will lead to protein phosphorylation which is catalysed by PKC.
• This will causes more Ca+ channel to open.

Question 13

Describe how receptor works to ion channel.

Answer 13

• When an agonist such as nicotine, bind to a receptor like nicotinic, it will open up the ion channel which is the Na+
• Na+ will pass through the ion channel.
• This causes depolarisation to happen.

Question 14

Describe how the cytoplasmic/ nuclear receptors work

Answer 14

• Agonist have to pass through the cell membrane.
• Hence, agonist have to be lipophilic in character.
• The agonist will bind to the receptor.
• The binding of agonist to the receptor will causes the stabilising protein to be released from the agonist-receptor complex.
• Then, the agonist-receptor complex will transport to the nucleus.
• The complex will bind to the binding region of the DNA and this stimulate the gene transcription.
• Hence response will be produced.

Question 15

Describe how the receptor linked to enzymes.

Answer 15

• when the agonist bind to the receptor, this causes the receptor to undergoes dimerisation.
• The enzyme will be activated.
• Hence, the enzyme will undergoes phosphorylation so that gene transcription can occur.
• Thus, cellular response is produced.