Unit 1- Communication And Signalling

Question 1

What are examples of extra cellular signalling molecules?

Answer 1

Steroid hormones, peptide hormones and neurotransmitters.

Question 2

Describe a receptor molecule.

Answer 2

Proteins with a binding site for a specific signal molecule. Binding changes the conformation of the receptor.

Question 3

Why does a hydrophobic signal diffuse through membranes?

Answer 3

Hydrophobic signals can diffuse through bilayers and bind to intracellular receptors. This is because the tails in phospholipids are also hydrophobic.

Question 4

What is a transcription factor?

Answer 4

Proteins that when attached to DNA can stimulate or inhibit transcription, controlling if genes are transcribed into mRNA.
Receptors for hydrophobic signalling molecules are transcription factors.

Question 5

What are examples of hydrophobic signals?

Answer 5

Thyroxine, steroid hormones (testosterone, oestrogen).

Question 6

What is a hormone receptor complex?

Answer 6

Steroid hormones binding to specific receptors in the cytosol or nucleus.

Question 7

What are hormone response elements (HREs)?

Answer 7

The specific DNA sequences the hormone receptor complex binds to.

Question 8

Describe the pathway of steroids.

Answer 8

1) Steroid hormones passes through plasma membrane into nucleus.

2) Hormones binds to receptor (transcription factor).

3) Hormone-receptor complex binds to specific sites on DNA (HRE)

4) Rate of transcription and gene expression is affected.

Question 9

Describe hydrophilic signalling molecules.

Answer 9

These bind to transmembrane receptors and don’t enter the cytosol. Such as peptide hormones and neurotransmitters.

Question 10

Describe hydrophilic signalling.

Answer 10

The hydrophilic signalling molecule binds to the receptor changing conformation. The signal is then transducer across the plasma membrane.

Question 11

What is a G protein?

Answer 11

Proteins which relay signals FROM hydrophilic signalling receptors TO enzymes and ion channels.

Question 12

Describe a cascade of phosphorylation.

Answer 12

A series of events with one kinase activating the next in the sequence and so on.
This can result in phosphorylation of many proteins and allow many intracellular signalling pathways to be activated.

Question 13

What is GLUT4?

Answer 13

A transporter protein that allows glucose to pass into cells by facilitated diffusion.

Question 14

Describe the process which occurs when insulin binds.

Answer 14

1) Insulin binds to receptor.

2) Receptor changes conformation triggering phosphorylation of the receptor.

3) This causes a phosphorylation cascade inside the cell.

4) This leads to vesicles containing GLUT 4 being transported to the cell membrane.

5) Glucose passes through the GLUT 4 transporter.

Question 15

Describe Type 2 diabetes mellitus.

Answer 15

Caused by a loss of insulin receptor function. Exercise triggers recruitment of GLUT4 so can improve uptake of glucose.

Question 16

Describe the resting potential.

Answer 16

Membrane potential (voltage) of a neuron that is not transmitting. A state of no net flow of ions across membrane. 60-80 mV.

Question 17

What is a nerve transmission?

Answer 17

A wave of depolarisation of the resting potential of a neuron. Depolarisation is a change in the voltage to a less negative value inside.

Question 18

What is an action potential (impulse)?

Answer 18

A wave of electrical excitation along a neurons plasma membrane.

Question 19

Describe a neurotransmitter and its receptor.

Answer 19

They initiate a response by binding to their receptors. Neurotransmitter receptors are ligand gated ion channels.

Question 20

Describe the steps involved in a nerve transmission.

Answer 20

1) The neurotransmitter binds to its receptor causing ion movement.

2) The ions cause a depolarisation (increase in voltage) of the plasma membrane.

3) If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, voltage gated sodium channels are triggered and sodium ions enter the cell down their concentration gradient.

4) This leads to a rapid and large change in membrane potential. After a short time sodium channels are inactivated.

5) Voltage gated potassium channels open allowing potassium ions to move out of the cell, restoring resting potential. (Repolarisation)

6) When the action potential reaches the end it causes neurotransmitter vesicles to fuse with membrane, stimulating a response in the connecting cell.

Question 21

Describe rod cells.

Answer 21

Photoreceptor cell in the retina sensitive to changes in light intensity.

Question 22

Describe cone cells.

Answer 22

Photoreceptor cells in the retina sensitive to specific colours.

Question 23

What is rhodopsin?

Answer 23

The retinal-opsin complex. Retinal molecule and opsin protein.

Question 24

Describe the Retinal response to light.

Answer 24

1) Retinal absorbs a photon of light and rhodopsin changes conformation to photo-excited rhodopsin.

2) A cascade of proteins amplify the signal.

3) Photo-excited rhodopsin activates the G protein (transducin). One photo-excited rhodopsin activates hundreds of G proteins.

4) Transducin (G protein) activates enzyme PDE.

5) PDE catalyses the hydrolysis of a molecule cyclic GMP. Each PDE breaks down thousands of cGMP.

6) The reduction in cGMP affects the function of ion channels in the membrane of rod cells.

7) Closure of ion channels, inward leakage of Na ions is halted so membrane potential increases.

8) Hyperpolarisation triggers nerve impulses in neurons in the retina.