Cell signalling III

Question 1

What is the Generalised Structure of Cell Surface Receptors?

Answer 1

Cell surface receptors are integral membrane proteins and, as such, have regions that contribute to three basic domains:

Extracellular domains: Ligand binding

Transmembrane domains: Serve to anchor the receptor in the membrane

Cytoplasmic or intracellular domains: Tails or loops of the receptor that are within the cytoplasm (effector region)

Question 2

Describe Lipophobic Messengers?

Answer 2

Lipophobic messengers cannot permeate the plasma membrane

Their receptors are located on the plasma membrane and face the extracellular fluid

The receptors for these messengers fell into three major classes

Response of the target cell is either by
Movement of ions, or phosphorylation of enzymes

Question 3

List the types of cell surface receptors?

Answer 3

Ion channel receptor
G protein linked receptor
Enzyme linked receptor

Question 4

What are ion channel linked receptor?

Answer 4

They are ion channels that open or close in response to the binding of a chemical messenger to a receptor

Also called ligand gated channels/ ion-channel-coupled receptor/transmitter-gated ion channels

Ion permeability of the plasma membrane are determined by the presence of ion channels

These ion channels are specific

Question 5

What two categories does ion channel linked receptor falls into?

Answer 5

Fast channels in which the receptor and channel are same protein

Slow channels in which the receptor and channel are separate proteins and linked together by a third type of protein, G-protein

Question 6

What are fast ligand gated channels? (1)

Answer 6

They function as both receptors and ion channels

Action is direct

Involved in rapid synaptic signalling between nerves cells and other electrically excitable target cells

Question 7

What are fast ligand gated channels? (2)

Answer 7

Binding of ligand causes channel to open, increasing the membrane’s permeability for that specific ion

Change in transport of ions through channel causes target response

Question 8

What does binding a messenger to the receptor do?

Answer 8

Opens the ion channels

Question 9

In fast ligand channels, what does opening the ion channels result in?

Answer 9

opening of most channels = in the movement of ions into or out of the cell

Question 10

Ions that move through an open channel ___?(FL-GC)

Answer 10

carry with them a charge which change the electrical properties of the cell

Question 11

Explain Signal transduction mechanisms for response mediated by Fast ligand-gated calcuim channels? (1)

Answer 11

Binding of the messenger to the receptor/channel complex opens calcium channels

Calcium ions entering the cells can trigger a variety of responses by interacting with intracellular proteins

Question 12

Explain Signal transduction mechanisms for response mediated by Fast ligand-gated calcuim channels? (2)

Answer 12

Calcuim can aslo function as a second messenger. It binds to a protein calmodulin . The calcuim-calmodulin complex activates a protein kinase which phosphorylates functional proteins and alter their structure and function

Question 13

What are enzyme linked receptors? (1)

Answer 13

They are receptors that function as enzymes and as receptors
Receptor and enzyme = same protein

They are transmembrane proteins, with the receptor side facing the interstitial fluid and the enzyme side facing the cytosol

Question 14

What are enzyme linked receptors? (2)

Answer 14

Ligand binding to the receptor activates the enzyme-Action is direct

Activated enzyme causes target response

Most enzyme linked receptors are Tyrosine kinases : RTKs (receptor tyrosine kinases ). Ex : Insulin receptor

Question 15

Explain Signal transduction mechanisms for response mediated by Enzyme-Linked Receptors? (1)

Answer 15

A messenger binds to the receptor, changing its conformation

The conformation change activates the tyrosine kinase which becomes phsophorylated

The phsophoryaletd tyrosine kinase can phsophorylates other intracellular proteins

Phosphorylation of the proteins changes its activity by covalent modification

Question 16

What are G-protein linked receptors? (1)

Answer 16

A receptor which classed G protein-linked receptor, when activated by binding to its ligand, results in the activation of a G-protein that conveys the message to the next component in the signal pathway

Question 17

What are G-protein linked receptors? (2)

Answer 17

G-proteins ( GTP binding proteins) located on the intracellular side of the plasma membrane, where they functions as a link between the G protein-linked receptors and other proteins in the plasma membrane called effectors:
Ion channels, or amplifier enzymes

Question 18

What are G-protein linked receptors? (3)

Answer 18

There is a vast number of receptors in this class, and they include receptors for glucagon, epinephrine, serotonin

Question 19

Explain Signal transduction mechanisms for response mediated by G Protein-Linked Receptors? (1)

Answer 19

G Protein-Linked Receptors and Slow Ligand-Gated Channels

G Protein-Linked Receptors and G proteins Regulated Enzymes