Communication and signalling

Question 1

What do multicellular organisms signal between?

Answer 1

Multicellular organisms signal between cells using extracellular signalling molecules.

Question 2

What are receptor molecules of target cells?

Answer 2

Receptor molecules of target cells are proteins with a binding site for a specific signal molecule.

Question 3

What happens when receptor molecules of a target cell bind to a specific signal molecule?

Answer 3

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

Question 4

What can only be detected and responded to by cells with the specific receptor?

Answer 4

Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor.

Question 5

What happens in multicellular organisms (in relation to signalling)?

Answer 5

In a multicellular organism, different cell types may show a tissue-specific response to the same signal.

Question 6

Can hydrophobic signalling molecules diffuse through the phospholipid bilayer?

Answer 6

Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayers of membrane, and so bind to intracellular receptors.

Question 7

What are the receptors for hydrophobic signalling molecules?

Answer 7

The receptors for hydrophobic signalling molecules are transcription factors.

Question 8

What are examples of hydrophobic signalling molecules?

Answer 8

The steroid hormones oestrogen and testosterone are examples of transcription factors/hydrophobic signalling molecules.

Question 9

Where do steroid hormones bind to?

Answer 9

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

Question 10

Where does the horomone-receptor complex move to?

Answer 10

The hormone-receptor complex binds to
specific DNA sequences called hormone
response elements (HREs). Binding at these
sites influences the rate of transcription, with
each steroid hormone affecting the gene
expression of many different genes.

Question 11

Where do hydrophobic signalling molecules bind to?

Answer 11

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

Question 12

What happens when transmembrane receptors bind to a ligand?

Answer 12

Transmembrane receptors change conformation when the ligand binds to the extracellular face.

Question 13

Does the signal molecule enter the cell when transmembrane receptors bind to a ligand?

Answer 13

The signal molecule does not enter the cell, but the signal is transduced across the plasma membrane.

Question 14

What do transmembrane receptors act as?

Answer 14

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

Question 15

What involves G-proteins or cascades of phosphorylation by kinase enzymes?

Answer 15

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

Question 16

What do phosphorylation cascades allow?

Answer 16

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

Question 17

What does binding of a peptide hormone insulin to its receptor result in?

Answer 17

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.

Question 18

What is diabetes mellitus caused by?

Answer 18

Diabetes mellitus can be caused by failure to produce insulin (type 1) or loss of receptor function (type 2).

Question 19

What is type 2 generally associated with?

Answer 19

Type 2 is generally associated with obesity.

Question 20

What also triggers more recruitment of GLUT4?

Answer 20

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

Question 21

What is the resting membrane potential?

Answer 21

The resting membrane potential is a state where there is no net flow of ions across the membrane.

Question 22

What does the transmission of a nerve impulse require?

Answer 22

The transmission of a nerve impulse requires changes in the membrane potential of the neurons plasma membrane.

Question 23

What is an action potential?

Answer 23

An action potential is a wave of electrical excitation along a neuron’s plasma membrane.

Question 24

What do neurotransmitters initiate?

Answer 24

Neurotransmitters initiate a response by binding to their receptors at a synapse.

Question 25

What is depolarisation of the plasma membrane a result of?

Answer 25

Depolarisation of the plasma membrane as a result of the entry of positive ions triggers the opening of voltage-gated sodium channels, and further depolarisation occurs.

Question 26

What restores the resting membrane potential?

Answer 26

Inactivation of the sodium channels and the opening of potassium channels restores the resting membrane potential.

Question 27

What causes neighbouring regions of membrane to depolarise?

Answer 27

Depolarisation of a patch membrane causes neighbouring regions of membrane to depolarise and go through the same cycle as adjacent voltage-gated sodium channels are opened.

Question 28

What happens when the action potential reaches the end of the neuron?

Answer 28

When the action potential reaches the end of the neuron it causes vesicles containing a neurotransmitters to fuse with the membrane- this releases the neurotransmitter, which stimulates a response in a connecting cell

Question 29

What does restoration of the resting potential membrane allow?

Answer 29

Restoration of the resting membrane potential allows the inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response to depolarisation of the membrane.

Question 30

What actively transports excess ions in and out of the cell?

Answer 30

Ion concentration gradients are re-established by the sodium-potassium pump, which actively transports excess ions in and out the cell.

Question 31

What is the retina?

Answer 31

The retina is the area within the eye that detects light and contains two types of photoreceptor cells: rods and cones.

Question 32

How do rods function?

Answer 32

Rods function in dim light but do not allow colour perception.

Question 33

What are cones responsible for?

Answer 33

Responsible for colour vision and only function in bright light.

Question 34

What does light-sensitive retinal combine within animals?

Answer 34

In animals the light-sensitive molecule retinal is combined with a membrane protein, opsin, to form the photoexcited rhodopsin.

Question 35

What is rhodopsin in rod cells?

Answer 35

In rod cells, the retinal-opsin complex is called rhodopsin.

Question 36

What does retinal absorb?

Answer 36

Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin.

Question 37

What does a cascade of proteins do?

Answer 37

A cascade of proteins amplifies the signal.

Question 38

What does photoexcited rhodopsin activate?

Answer 38

Photoexcited rhodopsin activates a G-protein, called transducin, which activates the enzyme phosphodiesterase (PDE).

Question 39

What does PDE do?

Answer 39

PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP).

Question 40

What does the hydrolysis of cGMP do?

Answer 40

This results in a closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina.

Question 41

What does a very high degree of amplification result in?

Answer 41

A very high degree of amplification results in rod cells being able to respond to low intensities of light.

Question 42

What happens when opsin combines with retinal in cone cells?

Answer 42

In cone cells, different forms of opsin combine with retinal to give different photoreceptor proteins, each with a meximal sensitivity to specific wavelengths: red, green, blue or UV