Intro to Pharm and Tox Topics
Signal transduction refers to the process by which a signal is transmitted from the outside of the cell to the cytoplasm. This is the way of action of most hormones and drugs. Receptors are the specific binding sites that transduce physicochemical signals. There are four main types of receptors: ion channels, G-protein coupled, enzymatic and transcription factors.
Physically/chemically-gated ion channels open in response to a ligand or physical stimuli. This allows a specific type of ion to flow into or out of the cell, with an instantaneous cellular response (milliseconds). G-protein coupled receptors (GPCR) have a slower response (hundreds of milliseconds).
Receptors with enzyme activity are usually kinases, or work in conjunction with kinases. There are six types: tyrosine kinase, cytokine, hematopoietic, serine/threonine kinase, tumor necrosis factor and guanylyl cyclase. Cytokine receptors are not kinases but they act by recruiting tyrosine kinases. Cytokine receptor I activates Ras, and cytokine receptor II activates STATS, both of which produce signals to change gene expression.
Hematopoietic receptors transduce signals for the production of antigens. Examples of serine/threonine receptors are the transforming growth factor family. The tumor necrosis factor family are not kinases but have a "death" domain whose signals result in cell death. Guanylyl cyclase converts GTP to cGMP.
Transcription factors signal for gene expression, an example are the steroid receptors.
The tranduction cascade sequence of events starts with the binding of hormone or drug (agonist) to its receptor. The agonist-receptor complex then interacts with another protein, usually a G-protein, which then produces a second messenger or activates another protein that does. Transduction cascades have two main advantages: they amplify the message and allow an agonist to have a variety of effects at the same time. The multiple effects are achieved by interacting with different receptors, which can in turn affect the production of diverse second messengers.
Continue to "Second
Messengers" or take a quiz: [Q1] [Q2]
[Q3] [Q4].
Need more practice? Answer the review questions below (after the sponsor).
1- What is signal transduction?
2- What are receptors?
3- List 4 main types of receptors
4- In general, how do physico/chemically-gated ion channels work?
5- What kind of activity(es) do enzymatic receptors have?
6- List 6 types of enzymatic receptors
7- What is the activity and function of cytokine receptors?
8- What is the function of hematopoietic receptors?
9- Give one example of a serine/threonine receptor.
10- What is the activity and function of the tumor necrosis factor family of receptors
11- What is the activity of guanylyl cyclase?
12- What is the activity of transcription
factors?
13- What is the first event in a
generic transduction cascade?
14- What is the second event in a
generic transduction cascade?
15- What is the third event in a
generic transduction cascade?
16- List 2 main advantages of transduction
cascades
17- How are several effects achieved at the same time by transduction cascades?
Continue scrolling to answers below (fter the sponsor).
Hey! DON'T PEEK!!! Finish the questions fist!
Answers:
1- What is signal transduction?
Process by
which a signal is transmitted from the outside of the cell to the cytoplasm
2- What are receptors?
Specific binding sites that transduce physicochemical
signals.
3- List 4 main types of receptors
ion channels
G-protein coupled receptors
enzymatic receptors
transcription factors
4- In general, how do physico/chemically-gated
ion channels work?
They open in response to a ligand or physical stimuli,
allowing a specific type of ion to flow in or out of the cell, with an instantaneous
response (milliseconds).
5- What kind of activity(es) do enzymatic
receptors have?
Enzymatic receptors are usually kinases or work in conjunction
with kinases, but may have other activities.
6- List 6 types of enzymatic receptors
tyrosine kinase
cytokines
hematopoietic receptors
serine/threonine kinases
tumor necrosis factor
guanylyl cyclase
7- What is the activity and function
of cytokine receptors?
They act by recruiting kinases. Cytokine receptor I activates
Ras and cytokine receptor II activates STATS, both of which produce signals
to change gene expression
8- What is the function of hematopoietic
receptors?
Transduce signals for the production of antigens.
9- Give one example of a serine/threonine
receptor.
The transforming growth factor family
10- What is the activity and function
of the tumor necrosis factor family of receptors?
They have a "death" domain whose signals result
in cell death.
11- What is the activity of guanylyl
cyclase?
Converts GTP to cGMP.
12- What is the activity of transcription
factors?
They signal for gene expression.
13- What is the first event in a
generic transduction cascade?
Binding of a hormone or drug (agonist) to its receptor.
14- What is the second event in a
generic transduction cascade?
The agonist-receptor complex interacts with another protein,
usually a G-protein.
15- What is the third event in a
generic transduction cascade?
The activated protein produces a second messenger or activates
another protein that does.
16- List 2 main advantages of transduction
cascades
message amplification
variety of effects at the same time
17- How are several effects achieved
at the same time by transduction cascades?
By interacting with different receptors, which can in
turn affect the production of diverse second messengers.
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