Signalling And Receptors

Question 1

Give 2 types of intercellular signalling

Answer 1

Signalling by secreted molecules - signalling cell releases a signalling molecule that is recognised by a specific receptor on a target cell
Signalling by plasma membrane bound molecules - the target and signalling cells are adjacent

Question 2

State and describe 3 methods that cells secrete molecules for signalling

Answer 2

Paracrine- mediated by local chemical mediator cells. This is for cells close to each other (within the same tissue)
Endocrine - signalling molecules are released into the blood stream and travel to cells in other tissues (distal)
Synaptic - nerve cells , specialised signalling between nerves and nerves or muscles. Signalling molecules are called neurotransmitters and cross a synapse

Question 3

What are the 3 subdivisions of signalling molecules?

Answer 3

Relocalise chemical mediators
Hormones
Neurotransmitters
(Some can be both though)

Question 4

Where can receptors be found ? And what are they in different places?

Answer 4

Cell surface receptors- on the plasma membrane. For hydrophilic (non lipid double) molecules that can’t pass through the membrane
Intracellular receptors-in the nucleus. For lipid soluble (small hydrophobic) molecules that can pass through membrane. Normally carried on a carrier protein like albumin.

Question 5

What do molecules with intracelluar receptors do?

Answer 5

Work to activate or inhibite genes, work at a dna level

Question 6

What is a receptor?

Answer 6

A molecule that recognises specifically a second molecule (ligand) or family of molecules and responds to ligand binding by bringing about regulation of a cellular process

Question 7

What does a receptor do in an unbound state and why?

Answer 7

Receptor is silent (doing nothing). This stops random signalling.

Question 8

What is a ligand?

Answer 8

A ligand is any molecule that binds specifically to a receptor site.

Question 9

What are the different types of ligand?

Answer 9

Agonists - ligand binding causes activation of a receptor
Antagonist - ligand binding prevents activation (doesn’t deactivate but competitively inhibites so no signal is sent when bound)

Question 10

What are the roles of receptors in cellular physiology?

Answer 10

Signalling
Neurotransmission
Cellular delivery (looking for nutrients)
Control of gene expression (intracelluar)
Cell adhesion
Release of calcium stores

Question 11

Describe the binding affinity of receptors and enzymes comparatively.

Answer 11

Receptors have much lower concentrations of signalling molecule than enzymes have of substrate so receptors have a much higher affinity.

Question 12

How are receptors classified?

Answer 12

Specific molecule they recognise (agonist)
Affinity to a series of antagonist
(Used more for when there are multiple receptors for one molecule so use affinity to sub classify).

Question 13

What are the 2 types of acetylcholine receptors?

Give receptor type and agonist

Answer 13

Nicotinic which recognises nicotine

Muscarinic which recognises muscadine

Question 14

What’s the difference between a receptor or acceptor?

Answer 14

Receptors- silent at rest. Agonist binding stimulates a biological response.
Acceptors- operate without ligand being bound.

Question 15

Methods of signal transduction

How signalling molecules get through membranes

Answer 15

1. Membrane-bound receptors with ion channels.
   Fastest but difficult to maintain.
2. Membrane bound receptors with enzyme activity.
   The receptor and effector are the same molecule.
3. Membrane bound receptors which couple to effector through translucent proteins.
4. Intracelluar receptors.

Question 16

What is the structure of a nicotinic acetylcholine receptor?

Answer 16

It is made of 5 subunits. It is a Chanel which a gated pore. Once acetylcholine binds there is a conformational change and the gate opens. It is selective for cations.

Question 17

Describe the structure of the insulin receptor.

Answer 17

Made if both alpha an beta sections translated as a signal protein. Extracellualr space is the insulin binding domain. Then a transmembrane domain that goes through the membrane. Tyrosine kinase domain in the cytoplasm.

Question 18

Describe membrane-bound receptors that signal through transducing proteins.

Answer 18

Coupled through g-protiejsbto enzymes or channels

Question 19

Describe the structure of G-protein coupled receptors

Answer 19

Have 2 binding domains 1 outside the cell and 1 in the membrane, and a G-protein coupling domain. 7 rod like (alpha helix)structures in a circle around the binding domain.

Question 20

Describe amplification in cellular signalling

Answer 20

1 signaling molecule could activate many GTP molecules. These could release many secondary messaging eras which all effect enzymes which could create much product. So at each level of transmission each molecule transmits to multiple other molecules.

Question 21

Describe how inhibitory protein complexes can inhibit

Answer 21

When they bind to the receptor they cause a conformational change in the binding site (active site) meaning the signalling molecule can no longer be recognised. Steroid hormones can release inhibitory proteins activating the binding site if receptors again.