Communication and Signalling 1.4

Question 1

what do multicellular organism signal between cells use?

Answer 1

extracellular signalling molecules

Question 2

what are receptor molecules of target cells?

Answer 2

proteins with a binding site for a specific signal molecule

Question 3

what happens when the receptor binds?

Answer 3

binding changes the conformation of the receptor
- initiates a response within the cell

Question 4

different cell types produce specific signals that can only be detected and responded to by what?

Answer 4

cells with the specific receptor

Question 5

in a multicellular organism, different cell types may show what?

Answer 5

tissue-specific response to the same signal

Question 6

how can hydrophobic signalling molecules diffuse?

Answer 6

they can diffuse directly through the phospholipid bilayers of membranes, and so bind to the intracellular receptors

Question 7

what are the receptors for the hydrophobic signalling molecules?

Answer 7

transcription factors

Question 8

give examples of hydrophobic signalling molecules

Answer 8

steroid hormones
- oestrogen
-testosterone

Question 9

where do steroid hormones bind?

Answer 9

they bind to specific receptors in the cytosol or the nucleus

Question 10

what does the hormone-receptor complex do?

Answer 10

it moves to the nucleus where it binds to specific sites on DNA and affect gene expression

Question 11

where do hydrophilic signalling molecules bind?

Answer 11

they bind to transmembrane receptors and do not enter the cytosol

Question 12

what happens to transmembrane receptors when a ligand binds to the extracellular face?

Answer 12

the receptors change conformation

Question 13

what happens to the signal molecule if it does not enter the cell?

Answer 13

signal is transduced across the plasma membrane

Question 14

how do transmembrane receptors act?

Answer 14

they act as signal transducers by converting the extracellular ligand binding event into intracellular signals
- alters behaviour of the cell

Question 15

describe the intracellular signalling cascade that is resulted from insulin

Answer 15

• binding of peptide hormone insulin to its receptors results in an intracellular signalling cascade (ISC)
• this ISC triggers the recruitment of GLUT4 transporter proteins to the cell membrane of fat and muscle cells

Question 16

how is type 1 diabetes mellitus caused?

Answer 16

failure to produce insulin

Question 17

how is type 2 diabetes mellitus caused?

Answer 17

loss of receptor function

Question 18

what is type 2 diabetes generally associated with?

Answer 18

obesity

Question 19

how can exercise be beneficial to someone with type 2 diabetes?

Answer 19

triggers the recruitment of GLUT4
- improves the uptake of glucose to fat and muscle cells

Question 20

what is resting membrane potential?

Answer 20

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

Question 21

what is required for the transmission of a nerve impulse?

Answer 21

a change in the membrane potential of the neuron’s plasma membrane

Question 22

what is action potential?

Answer 22

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

Question 23

how do neurotransmitters initiate a response?

Answer 23

by binding to the receptors at a synapse

Question 24

what is the result of a depolarisation of the plasma membrane ?

Answer 24

the entry of positive ions triggers the opening of voltage-gated sodium channels
- further depolarisation occurs

Question 25

what restores the resting membrane potential?

Answer 25

inactivation of the sodium channels and the opening of the potassium channels

Question 26

what does depolarisation of a patch of membrane cause?

Answer 26

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

Question 27

how are ion concentration gradients re-established?

Answer 27

by the sodium-potassium pump - actively transports excess ions in and out of the cell

Question 28

what is the retina?

Answer 28

an area within the eye that detects light

Question 29

what are the two types of photoreceptor cells that the retina contains?

Answer 29

rods cand cones

Question 30

how are photoreceptors of the eye in animals formed?

Answer 30

light-sensitive molecule retinal is combined with a membrane protein called opsin

Question 31

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

Answer 31

rhodopsin

Question 32

what does a very high degree of amplification of rod cells result in?

Answer 32

the ability to respond to low intensities of light

Question 33

describe what happens in cone cells

Answer 33

different forms of opsin combine with retinal to give different photoreceptor proteins
- each with a maximal sensitivity to specific wavelengths: red, green, blue and UV

Question 34

what is involved in transducer hydrophilic signals?

Answer 34

G-proteins or cascades of phosphorylation by kinase enzymes

Question 35

what do phosphorylation cascades allow?

Answer 35

they allow more than one intracellular signalling pathway to be activated

Question 36

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

Answer 36

cause vesicles containing neurotransmitter to fuse with the membrane - this releases neurotransmitter, which stimulates a response in a connecting cell

Question 37

what does the restoration of the resting membrane potential allow?

Answer 37

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

Question 38

describe what happens when retinal absorbs a photon of light

Answer 38

• rhodopsin changes conformation to photoexcited rhodopsin
• a cascade of proteins amplifies the signal
• photo excited rhodopsin activates a G-protein called transducin - activates the enzyme phosphodiesterase (PDE)
• PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP)
• results in closure of ion channels in the membrane of rod cells - triggers the impulses in neuron’s in retina