III. Signal transduction and cell cycle | 38. Classification and function of membrane receptors

Question 1

I. Cell surface receptor
1. What is Cell surface receptor?

Answer 1

Cell surface (or membrane) receptors are receptors found outside of the plasma membrane.

Question 2

I. Cell surface receptor
2. What is the mechanism of Cell surface receptors?

Answer 2

• They bind ligands which are too hydrophilic or too big to cross the plasma membrane of the target cell.
• The receptor protein binds to the extracellular signal, generating new intracellular signals which result in a cascade of intracellular signal molecules.

Question 3

I. Cell surface receptor - Types of extracellular signals
3A. What are the 4 types of extracellular signals?

Answer 3

1. Endocrine
2. Paracrine
3. Autocrine
4. Juxtacrine

Question 4

I. Cell surface receptor - Types of extracellular signals
3B. What is the feature of endocrine signals?

Answer 4

signal released into organism’s blood stream (SLOW!)

Question 5

I. Cell surface receptor - Types of extracellular signals
3C. What is the feature of Paracrine signals?

Answer 5

Paracrine: molecule diffuses locally through ECF and come in contact with target cell
(FAST!)

Question 6

I. Cell surface receptor - Types of extracellular signals
3C. What is the feature of Autocrine signals?

Answer 6

Autocrine: cell responds to signals they produce themselves
(FAST!)

Question 7

I. Cell surface receptor - Types of extracellular signals
3D. What is the feature of Juxtacrine signals?

Answer 7

Juxtacrine: requires close contact – a ligand on one cell binds to a receptor on the other

Question 8

I. Cell surface receptor
4. What are the functions of intracellular signaling pathways?

Answer 8

he components of the intracellular signaling pathways perform one or more crucial functions:
1) They can relay the signal forward, thereby help spread it through the cell
2) They can amplify the signal received, so that only few EC signals are enough to evoke a large IC response
3) They can receive signals from more than one signaling pathway and integrate them before sending it forward
4) They can distribute the signal to more than one signaling pathway or effector protein, evoking a more complex response

Question 9

II. Types (classification) of receptors
1. Explain the specificity of signaling molecules?

Answer 9

All signaling molecules bind to specific receptors that act as signal transducers, converting a ligand-receptor complex into an intracellular signal that affects cellular function (response).

Question 10

II. Types (classification) of receptors
2. What are the 3 types of receptors?

Answer 10

1. Ligand-gated ion channels (ionotropic receptors)
2. G-protein coupled receptors (GPCR)
3. Enzyme-linked receptors

Question 11

II. Types (classification) of receptors
3A. What is the mechanism of Ligand-gated ion channels (ionotropic receptors)?

Answer 11

• Binding of EC signals (e.g. neurotransmitters) makes the channel either open or close.
• If it opens, it allows a flow of specific ions such as Na+, K+, Cl-.
• Driven by electrochemical gradients, the ions will either move in or out of the cell.
• This will create a rapid change in membrane potential, leading to a response (e.g. triggering a nerve impulse)
• Example: nicotinic ACh receptor

Question 12

II. Types (classification) of receptors
3B. Give an example of Ligand-gated ion channels (ionotropic receptors)?

Answer 12

• Binding of EC signals (e.g. neurotransmitters) makes the channel either open or close.
• If it opens, it allows a flow of specific ions such as Na+, K+, Cl-.
• Driven by electrochemical gradients, the ions will either move in or out of the cell.
• This will create a rapid change in membrane potential, leading to a response (e.g. triggering a nerve impulse)
• Example: nicotinic ACh receptor

Question 13

II. Types (classification) of receptors
4A. What is the mechanism of G-protein coupled receptors (GPCR)?

Answer 13

• Activated membrane-bound, trimeric GTP-binding proteins (G-proteins) which then activate either an enzyme or an ion channel in the plasma membrane.
• This will initiate a cascade of further effects.
• These receptors mediate response to a diversity of EC signals (hormones, neurotransmitters, peptides, fatty acids).

Structure: single polypeptide chain crossing
the plasma membrane 7 times = 7TM
Example: muscarinic ACh receptor

Question 14

II. Types (classification) of receptors
4B. What is the structure of G-protein coupled receptors (GPCR)?

Answer 14

single polypeptide chain crossing the plasma membrane 7 times = 7TM

Question 15

II. Types (classification) of receptors
4C. What is the example of G-protein coupled receptors (GPCR)?

Answer 15

muscarinic ACh receptor

Question 16

II. Types (classification) of receptors
5A. What are the features of Enzyme-linked receptors?

Answer 16

• They can either have their own enzyme or rely on another enzyme that becomes associated with the active receptor.
• Most are associated with protein kinases where ligand binding causes phosphorylation of a protein, which then activates or inhibits its activity
• Example: Tyrosine-kinase, Ser/Thr-kinase

Question 17

II. Types (classification) of receptors
5B. What are the examples of Enzyme-linked receptors?

Answer 17

Tyrosine-kinase, Ser/Thr-kinase,

Question 18

III. Signal transduction pathway
1. What is Signal transduction?

Answer 18

conversion of the information to chemical processes.

Question 19

III. Signal transduction pathway
2. The biological response of signal transduction may emerge through….

Answer 19

• Switching existing proteins on/off (quicker)
  +) Allosteric regulation
  +) Covalent modification: phosphorylation
  +) Regulation of degradation
  +) Formation of a complex
  +) Alteration of subcellular localization
• Altering the set of proteins by the regulation of gene expression (slower)

Question 20

III. Signal transduction pathway
3. What is the modular framework of Signal transduction pathway?

Answer 20