Lecture 19

Question 1

Juxtacrine signalling is an example of a short-range signalling mechanism. Outline how this signalling mechanism acts

Answer 1

In juxtacrine signalling, two cells are in direct contact and the ligand is a membrane-bound signal molecule (transmembrane protein)

Question 2

List some of the downstream effects of signalling mechanisms on the cell

Answer 2

Survival, death(apoptosis), migration, differentiation, division

Question 3

What is often the result of phosphorylation of receptors once they become activated

Answer 3

Phosphorylation of receptors often creates recognition (docking) sites for downstream protein binding

Question 4

Which kind of short-range signalling involves ligand secretion from the signalling cell which acts as a local mediator on neighbouring cells, diffusing only a few cell diameters away

Answer 4

Paracrine

Question 5

Where in the body is autocrine signalling often used

Answer 5

Used a lot in the immune system

Question 6

In addition to paracrine, autocrine and juxtacrine signalling, there is another type of short range cell signalling. What is this signalling mechanism and how does it act

Answer 6

Short range signalling can also occur through gap junctions. Gap junctions act to physically connect cells together and allows them to share small molecules and ions. This acts to metabolically and electrically couple cells together and allows the transfer of species such as cAMP and Ca2+ between cells.

Question 7

Cells of different types can respond to the same signal quite differently. Give an example of this

Answer 7

The response of different cells to acetylcholine can vary in different tissues. In the heart, release of acetylcholine causes the relaxation of cardiac muscle whereas in skeletal muscle it causes contraction. Similarly, in glandular tissue, acetylcholine release causes secretion of vesicles

Question 8

How many transmembrane domains are indicative of GPCRs

Answer 8

7 transmembrane domains

Question 9

What is meant by the term signal transduction

Answer 9

The process by which extracellular signalling molecules cause changes in target cells

Question 10

Signalling pathways usually involve an extracellular signalling molecule and a receptor protein that leads to the activation of intracellular signalling. Give examples of the different downstream targets of intracellular signalling

Answer 10

Metabolic enzymes, gene regulatory proteins and cytoskeletal protein elements

Question 11

Integration steps often occur in intracellular signalling where different pathways can affect the same components. In contrast, spreading of the signal is never seen, T or F

Answer 11

F – spreading is also seen

Question 12

What is the other name given to ligand-gated ion channels

Answer 12

Inotropic receptors

Question 13

What is meant by primary transduction

Answer 13

Primary transduction is the process the converts the signal from the extracellular signalling molecule to an intracellular signal

Question 14

Intracellular amplification of signals is a common feature of signal transduction, T or F

Answer 14

T

Question 15

What are the two main types of GTP binding proteins involved in intracellular signalling

Answer 15

Guanine Exchange Factors (GEFs) and GTPase activating proteins (GAPs)

Question 16

What kind of proteins are often the downstream targets of intracellular receptors

Answer 16

Transcription factors

Question 17

What type of signalling molecules do cell surface receptors often interact with

Answer 17

Hydrophilic ligands

Question 18

What is the role of scaffold proteins in intracellular signalling

Answer 18

Scaffold proteins play an important role in anchoring numerous components in place to respond to the activated receptors. By holding components in place, scaffold proteins effectively increase the effective concentration

Question 19

Describe what is meant by autocrine signalling

Answer 19

Autocrine signalling involves local groups of neighbouring cells with both produce the receptor and the ligand for a particular pathway. The secreted factor activates its own receptor on the same cell and neighbouring cells often as part of a positive feedback loop.

Question 20

Describe the general structure and activation of enzyme-coupled receptors

Answer 20

Enzyme coupled receptors are transmembrane proteins that interact with ligands. This interaction then activates the intracellular enzyme domain or recruits an intracellular enzyme leading to signal transduction

Question 21

What kind of signalling molecules do intracellular receptors interact with

Answer 21

Hydrophobic/lipophilic signalling molecules

Question 22

Give an overview of signalling from GPCRs

Answer 22

The GPCR will interact with a ligand that allows binding of the receptor to a G-protein forming a complex which can then interact with enzymes