Hydrophilic Signals and Transduction

Question 1

Hydrophilic signalling molecules

Answer 1

Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol

Question 2

Examples of hydrophilic signalling molecules

Answer 2

Peptide hormones and neurotransmitters are examples of hydrophillic signalling molecules

Peptide hormone examples - insulin, glucagon
Examples of neurotransmitters - acetycholine, noradrenaline

Question 3

Transmembrane receptors

Answer 3

Transmembrane receptors change conformation when the ligand binds to the extracellular face; the signal molecule does not enter the cell but the signal is transduced across the plasma membrane.

Transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.

Question 4

Signal transduction

Answer 4

The extracellular ligand-binding event is converted into intracellular signals by transmembrane proteins acting as signal transducers.

Question 5

Transduced hydrophilic signals

Answer 5

Transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes

Question 6

G-proteins

Answer 6

G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.

Question 7

Phosphorylation cascades

Answer 7

Phosphorylation cascades allow more than one intracellular signalling pathway to be activated.

Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on.

Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.

Question 8

Types of hydrophillic signal receptors

Answer 8

Ion-channel linked, kinase linked, and G-protein linked

Question 9

Binding of insulin

Answer 9

Binding of the peptide hormone insulin to its receptor results in an intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.

Binding of insulin to its receptor causes a conformational change that triggers the phosphorylation of the receptor.

This starts a phosphorylation cascade inside the cell, which eventually leads to GLUT4- containing vesicle being transported to the cell membrane

Question 10

Causes of Diabetes

Answer 10

Type 1 - Failure to produce insulin

Type 2 - Loss of receptor function

Question 11

Type 2 diabetes

Answer 11

Type 2 diabetes is generally associated with obesity

Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2 diabetes.