Communication and Signalling

Question 1

Multicellular organisms signal between cells using?

Answer 1

Extracellular signalling molecules.

Question 2

Examples of extra cellular signalling molecules?

Answer 2

Steroid hormones, peptide hormones and neurotransmitters

Question 3

Receptor molecules of target cell are?

Answer 3

Proteins with a binding site for a specific signal molecule.

Question 4

How do receptors work?

Answer 4

Binding changes the conformation of the receptor which initiates a response within the cell.

Question 5

Different cell types produce —— ——

Answer 5

Specific signals

Question 6

The specific signals produced by different cell types can only be detected and responded to by cells with the —— ——

Answer 6

Specific receptor

Question 7

Signalling molecules may have different effects on different target cell types due to?

Answer 7

Differences in the intercellular signalling molecules and pathways that are involved.

Question 8

In a multicellular organism, differnt cell types may show a ———— response to the same signal

Answer 8

Tissue-specific

Question 9

How do hydrophobic signalling molecules interact with the cell?

Answer 9

Diffuse directly through the phospholipid bilayer of membranes and so bind to intercellular receptors.

Question 10

What are the receptors of hydrophobic signalling molecules called?

Answer 10

Transcription factors.

Question 11

What are transcription factors?

Answer 11

Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.

Question 12

Examples of hydrophobic signalling molecules?

Answer 12

Steroid hormones oestrogen and testosterone.

Question 13

How does hydrophobic signalling work?

Answer 13

Steroid hormones bind to specific receptors in the cytoskeleton or the nucleus. The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA called HRE’s. Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.

Question 14

How do hydrophilic signalling molecules interact with the cell?

Answer 14

Bind to transmembrane receptors and do not enter the cytosol.

Question 15

Examples of hydrophilic signalling molecules?

Answer 15

Peptide hormones and neurotransmitters.

Question 16

Stage 1 of hydrophilic signalling. (Reception)

Answer 16

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

Question 17

Stage 2 of hydrophilic signalling. (Transduction)

Answer 17

Transmembrane receptors act as signal transducers by converting the extra cellular ligand-binding event into intracellular signals, which alters the behaviour of the cell. Transduced hydrophilic signals involve G proteins or cascades of phosphorylation by kinase enzymes.

Question 18

Transduction by G proteins?

Answer 18

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

Question 19

Transduction by phosphorylation?

Answer 19

Phosphorylation cascades allow more than 1 intracellular signalling pathway to be activated. They involve a series of events with 1 kinase activating the next in the sequence and so on.

Question 20

Phosphorylation cascades can result in the phosphorylation of ——proteins as a result of the —— —— ——

Answer 20

many proteins as a result of the original signalling event

Question 21

Stage 3 of hydrophilic signalling. (Response)

Answer 21

Response of the cell will vary depending on the signal.

Question 22

INSULIN - binding of the peptide hormone to its receptor results in an?

Answer 22

Intracellular signalling cascade.

Question 23

INSULIN - What does this intracellular signalling cascade trigger?

Answer 23

The recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.

Question 24

INSULIN - what does insulin binding to its receptor cause?

Answer 24

A conformational change

Question 25

INSULIN - what does the conformational change caused by insulin binding to its receptor trigger?

Answer 25

Phosphorylation of the receptor.

Question 26

INSULIN - What does phosphorylation of the receptor start?

Answer 26

A phosphorylation cascade inside the cell.

Question 27

INSULIN - What does the phosphorylation cascade inside the cell lead to?

Answer 27

GLUT4 containing vesicles being transported to the cell membrane.

Question 28

What is diabetes caused by?

Answer 28

Failure to produce insulin (type 1) OR Loss or receptor function (type 2)

Question 29

What is type 2 diabetes generally associated with?

Answer 29

Obesity.

Question 30

What improves the uptake of glucose to fat and muscle cells in subjects with type 2 diabetes?

Answer 30

Exercise as it triggers the recruitment of GLUT4, so it can improve the uptake of glucose to fat and muscle cells in subjects with type 2

Question 31

What is resting membrane potential?

Answer 31

A state where there is no net flow of ions across the membrane.

Question 32

What does transmission of a nerve impulse require?

Answer 32

Changes in the membrane potential of the neuron’s plasma membrane.

Question 33

What is an action potential?

Answer 33

A wave of electrical excitation along a neurons plasma membrane.

Question 34

What do neurotransmitters do?

Answer 34

Initiate a response by binding to their receptors at a synapse.

Question 35

What are neurotransmitter receptors?

Answer 35

Ligand gated ion channels which open in response to binding.

Question 36

What do neurotransmitter receptors allow entry of? And what do they therefore cause.

Answer 36

+vely charged ions and therefore cause depolarisation of the plasma membrane.

Question 37

Depolarisation of the plasma membrane as a result of the entry of +ve ions triggers? And what occurs?

Answer 37

The opening of voltage gates sodium channels and further depolarisation occurs.

Question 38

What is depolarisation?

Answer 38

Change in the membrane potential to a less negative value inside.

Question 39

What restores the resting membrane potential?

Answer 39

Inactivation of Na channels and the opening of K channels.

Question 40

Restoration of the resting membrane potential allows?

Answer 40

The inactive voltage-gated Na channels to return to a conformation that allows them to open again in response to depolarisation of the membrane.

Question 41

Restoration of the resting membrane potential causes?

Answer 41

Ion concentration gradients to be reestablished by the sodium-potassium pump, which actively transports excess ions in and out of the cell.

Question 42

Restoration of the resting membrane potential - following repolarisation what happens?

Answer 42

Sodium and potassium ion concentration gradients are reduced. The sodium potassium pump restores the sodium and potassium ions back to resting potential levels.

Question 43

Neurotransmission? (7 steps)

Answer 43

1) Binding of neurotransmitter triggers the opening of ligand-gated ion channels at a synapse. 2) Ion movement occurs and there is depolarisation of the plasma membrane. 3) If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage gates Na channels is triggered and Na+ ions enter the cell down their electrochemical gradient. 4) This leads to a rapid and large change in the membrane potential. 5) A short time after opening, the Na channels become inactivated. 6) Voltage-gated K channels then open to allow K+ ions to move out of the cell to restore the resting membrane potential. 7) ion concentration gradients are reestablished by the sodium-potassium pump.

Question 44

What does depolarisation of a patch of membrane cause?

Answer 44

Neighbouring regions of the membrane to depolarise and go through the same cycle, as adjacent voltage-gated Na channels are opened.

Question 45

When the action potential reaches the end of the neuron it causes…

Answer 45

vesicles containing neurotransmitter to fuse with the membrane.

Question 46

When vesicles containing neurotransmitter fuse with the membrane what happens?

Answer 46

This releases neurotransmitter which stimulates a response in a connecting cell.

Question 47

What is the retina?

Answer 47

The area within the eye that detects light and contains 2 types of photoreceptor cells (Rods and cones)

Question 48

Rods?

Answer 48

Function in dim light but don’t allow colour perception.

Question 49

Cones?

Answer 49

Responsible for colour vision and only function in bright light.

Question 50

How rhodopsin formed?

Answer 50

In animals the light sensitive molecule retinal is combined with a membrane protein, opsin, to form the photoreceptors of the eye. In rod cells the retinal opsin complex is called rhodopsin.

Question 51

Generation of a nerve impulse is brought about when? (6 step process)

Answer 51

1) Retinal absorbs a photon of light and rhodopsin changes confirmation to photoexcited rhodopsin. 2) A cascade of phosphorylation amplifies the signal. Photoexcited rhodopsin activates a G protein (transducin), which activates the enzyme PDE. A single photoexcited rhodopsin activates 100s of molecules of G protein. 3) each activated G-protein activates 1 molecule of PDE 4) PDE catalyses the hydrolysis of a molecule called cGMP. Each active PDE molecule breaks down 1000s of cMGP molecules per second. 5) The reduction in cGMP concentration as a result of its hydrolysis affects the function of ion channels in the membrane of rod cells. This results in the closure of ion channels in the membrane of rod cells. 6) This triggers nerve impulses in neurons in the retina.

Question 52

What allows rod cells to be able to respond to low intensities of light?

Answer 52

A very high degree of amplification.

Question 53

What causes cone cells to allow colour vision?

Answer 53

Different forms of opsin combine with retinal to give different photoreceptor proteins, each with maximal sensitivity to specific wavelengths: red, green, blue or UV.