AH Biology - Unit 1 - KA4(c) - Hydrophilic Signals and Transduction

What are key examples of hydrophilic signals?

Key examples of hydrophilic signals are peptide hormones, such as insulin, and neurotransmitters.

How are hydrophilic signalling molecules passed onto the cell?

Hydrophilic signalling molecules cannot diffuse through membranes and bind to transmembrane receptors. They do not enter the cytoplasm, instead, the signal is transduced across the plasma membrane. Transmembrane receptors change conformation when the hydrophilic signal molecule, a ligand, binds to the extracellular face, the membrane on the outer surface of the cell.

What do transmembrane receptors act as?

Transmembrane receptors act as signal transducers. This means that they convert the extracellular ligand-binding event into an intracellular signal which alters the behaviour of the cell and brings about a response.

What do transduced hydrophilic signals often involve?

Transduced hydrophilic signals often involve:

• G-proteins

and/or

• Phosphorylation cascades by kinase enzymes

What do G-proteins do?

G-proteins relay signals from activated receptors to target proteins, such as enzymes or ion channels.

What do phosphorylation cascades involve?

Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on. More than one intracellular signalling pathway can be activated in this way. This phosphorylation can result in the phosphorylation of many proteins as a result of one original signalling event.

What is the process for the G-protein pathway?

The process for the G protein pathway is:

1. Signal molecule binds to the transmembrane receptor on the outer surface.

2. Receptor changes conformation to transduce the signal across the plasma membrane.

3. G-proteins relay the signal from activated receptors to target proteins, such as enzymes or ion channel proteins.

What is stage 1 of the process for the G-protein pathway?

Stage 1 for the process of the G-protein pathway is “Signal molecule binds to the transmembrane receptor on the outer surface.”

What is stage 2 of the process for the G-protein pathway?

Stage 2 for the process of the G-protein pathway is “Receptor changes conformation to transduce the signal across the plasma membrane.”

What is stage 3 of the process for the G-protein pathway?

Stage 3 for the process of the G-protein pathway is “G-proteins relay the signal from activated receptors to target proteins, such as enzymes or ion channel proteins.”

What is the process of the phosphorylation cascade?

The process of the phosphorylation cascade is:

1. Signal molecule binds to the transmembrane receptor on the outer surface.

2. Receptor changes conformation to transduce the signal across the plasma membrane.

3. The activated receptor triggers the activation of a kinase.

4. Each kinase phosphorylates and activates the next kinase/protein in the sequence.

5. This results in the phosphorylation of many proteins from one binding event.

What is stage 1 of the phosphorylation cascade?

Stage 1 of the phosphorylation cascade is “Signal molecule binds to the transmembrane receptor on the outer surface.”

What is stage 2 of the phosphorylation cascade?

Stage 2 of the phosphorylation cascade is “Receptor changes conformation to transduce the signal across the plasma membrane.”

What is stage 3 of the phosphorylation cascade?

Stage 3 of the phosphorylation cascade is “The activated receptor triggers the activation of a kinase.”

What is stage 4 of the phosphorylation cascade?

Stage 4 of the phosphorylation cascade is “Each kinase phosphorylates and activates the next kinase/protein in the sequence.”

What is stage 5 of the phosphorylation cascade?

Stage 5 of the phosphorylation cascade is “This results in the phosphorylation of many proteins from one binding event.”

What does the binding of the peptide hormone insulin to its receptors in fat and muscle cell plasma membranes cause?

The binding of the peptide hormone insulin to its receptors in fat and muscle cell plasma membranes causes a conformational change of the receptor proteins. This conformational change triggers the phosphorylation of the receptor. This starts a phosphorylation cascade inside the cell, which leads to the recruitment of the GLUT4 transporter protein to the cell membranes of fat and muscle cells. Vesicles transport the GLUT4 transporter to the plasma membrane.

What is type 1 diabetes caused by, and how can it be treated?

Type 1 diabetes is caused by a failure to produce insulin and is thought to be caused by an autoimmune disease. Type 1 diabetes can be treated by insulin injections.

What is type 2 diabetes caused by, and how can it be treated?

Type 2 diabetes is caused by a loss of receptor function. It is associated with obesity. Type 2 diabetes can be treated with lifestyle changes, particularly by increasing exercise levels.

What can exercise trigger in regards to type 2 diabetes?

Exercise can trigger the recruitment of GLUT4 transporter proteins, and so can improve the uptake of glucose to fat and muscle cells in subjects with type 2 diabetes.