Communication and Signalling

Question 1

How do multicellular organisms signal between cells?

Answer 1

Using extracellular signalling molecules.

Question 2

What are examples of extracellular signaling molecules?

Answer 2

Steroid hormones, peptide hormones and neurotransmitters.

Question 3

What are receptor molecules of target cells?

Answer 3

Proteins with a binding site for a specific signal molecule.

Question 4

What does the conformational change that occurs when a receptor binds result in?

Answer 4

A response within the cell.

Question 5

Why may signalling molecules have different effects on different target cell types?

Answer 5

Because of differences in the intracellular signalling molecules and pathways that are involved.

Question 6

What does hydrophobic signalling molecules being able to diffuse directly through the phospholipid bilayer allow?

Answer 6

The signalling molecule being able to bind to intracellular receptors.

Question 7

What are transcription factors?

Answer 7

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

Question 8

What are the receptors for hydrophobic signalling molecules?

Answer 8

Transcription factors.

Question 9

Where do steroid hormones bind?

Answer 9

To specific receptors in the cytosol or the nucleus.

Question 10

Where does the hormone-receptor complex move to?

Answer 10

The nucleus where it binds to the specific sites on DNA and affects gene expression.

Question 11

What does the hormone-receptor complex bind to?

Answer 11

Specific DNA sequences called Hormone Response Elements (HRE).

Question 12

What does binding at different HRE’s influence?

Answer 12

The rate of transcription, with each steroid hormone affecting the gene expression of many different genes.

Question 13

What do hydrophilic signalling molecules bind to?

Answer 13

Transmembrane receptors.

Question 14

Do hydrophilic signalling molecules enter the cytosol?

Answer 14

No.

Question 15

What are examples of hydrophilic extracellular signalling molecules?

Answer 15

Peptide hormones and neurotransmitters.

Question 16

How do transmembrane receptors act as signal transducers?

Answer 16

By converting the extracellular ligand-binding event into the intracellular signals, which alters the behaviour of the cells.

Question 17

What do transduced hydrophilic signals often involve?

Answer 17

G-proteins or cascades of phosphorylation by kinase enzymes.

Question 18

What allows more than one intracellular signalling pathway to be activated?

Answer 18

Phosphorylation cascades.

Question 19

What is the role of G-proteins?

Answer 19

To relay signals from activated receptors to target proteins such as enzymes and ion channels.

Question 20

What are phosphorylation cascades?

Answer 20

They 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 21

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

Answer 21

An intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.

Question 22

What does exercise trigger?

Answer 22

Recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in people with type 2.

Question 23

What is resting membrane potential?

Answer 23

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

Question 24

What does the transmission of a nerve impulse require?

Answer 24

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

Question 25

What is an action potential?

Answer 25

A wave of electrical excitation along a neuron’s plasma membrane.

Question 26

How do neurotransmitters initiate a response?

Answer 26

By binding to their receptors at a synapse.

Question 27

What are neurotransmitter receptors?

Answer 27

Ligand-gated ion channels.

Question 28

What is depolarisation?

Answer 28

A change in the membrane potential to a less negative value inside.

Question 29

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

Answer 29

Vesicles containing neurotransmitters fuse with the membrane which causes the release of the neurotransmitter.

Question 30

What is the retina?

Answer 30

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

Question 31

What is combined to form the photoreceptor of the eye?

Answer 31

The light sensitive molecule retinal and the membrane protein opsin.

Question 32

What is the retinal-opsin complex called in rod cells?

Answer 32

Rhodopsin

Question 33

What are rod cells responsible for?

Answer 33

Vision in dim light.

Question 34

What are cone cells responsible for?

Answer 34

Colour vision.

Question 35

Where is photopsin found?

Answer 35

Cone cells

Question 36

In cone cells, why do different forms of opsin combine with retinal?

Answer 36

To give different receptor proteins which each have a maximal sensitivity to a specific wavelength: red; green; blue or UV.