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Advanced Higher Biology > 1.4 Communication and Signalling > Flashcards

1.4 Communication and Signalling Flashcards

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1
Q

how do multicellular organisms signal between cells

A

using extracellular signalling molecules

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2
Q

what are examples of extracellular signalling molecules

A

steroid hormones
peptide hormones
neurotransmitters

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3
Q

what are receptor molecules of target cells

A

proteins with a binding for a specific signal molecule

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4
Q

why does binding change the conformation of the receptor

A

initiates a response within the cell

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5
Q

different cell types produce specific signals that can only

A

be detected and responded to by cells with the specific receptor

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6
Q

why can signalling molecules have different effects on different target cell types

A

due to differences in the intracellular signalling molecules and pathways that are involved

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7
Q

in a multicellular organism, different cell types may show

A

a tissue-specific response to the same signal

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8
Q

how do hydrophobic signalling molecules transport through the membrane

A

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

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9
Q

what are the receptors for hydrophobic molecules

A

transcription factors

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10
Q

what are transcription factors

A

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

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11
Q

what are examples of hydrophobic signalling molecules

A

steroid hormones
oestrogen
testosterone

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12
Q

what do steroid hormones bind to

A

specific receptors in the cytosol or the nucleus

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13
Q

where does the hormone-receptor complex move to

A

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

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14
Q

what do hormone-receptor complexes bind to

A

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

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15
Q

what do hydrophilic signalling molecules bind to

A

transmembrane receptors and do not enter the cytosol

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16
Q

what are examples of hydrophilic extracellular signalling molecules

A

peptide hormones

neuritransmitters

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17
Q

what happens when the ligand binds to the extracellular face

A

transmembrane receptors change conformation when when the ligand binds to the extracellular face
the signaling molecule does not enter the cell, but the signal is transduced across the plasma membrane

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18
Q

how do transmembrane receptors act as signal transducers

A

by converting the extracellular ligand-binding event into intracellular signal, which alters the behaviour of the cell

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19
Q

what do transduced hydrophilic signals often involve

A

G-proteins or cascades of phosphorylation by kinase enzymes

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20
Q

G-proteins relay signals from

A

activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels

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21
Q

what do phosphorylation cascades allow

A

more than one intracellular signalling pathway to be activated

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22
Q

what do phosphorylation cascades involve

A

a series of events with one kinase activating the next in the sequence and so on

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23
Q

what can phosphorylation cascades result in

A

the phosphorylation of many proteins as a result of the original signalling event

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24
Q

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

A

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

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25
Q

what does binding of insulin to its receptor cause

A

a conformational change that triggers phosphorylation of the receptor
this starts a phosphorylation cascade inside the cell, which eventually leads to GLUT4-containing vesicles being transported to the cell membrane

26
Q

what can diabetes mellitus be caused by

A

type 1 or type 2 diabetes

27
Q

what is type 1 diabetes

A

failure to produce insulin

28
Q

what is type 2 diabetes

A

loss of insulin receptor function

29
Q

what is type 2 diabetes associate with

A

obesity

30
Q

what triggers the recruitment of GLUT4

A

exercise

increase uptake of glucose to fat and muscle cells in subject with type 2

31
Q

what is the resting membrane potential

A

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

32
Q

what does the transmission of a nerve impulse require

A

changes in the membrane potential of the neuron’s plasma membrane

33
Q

what is an action potential

A

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

34
Q

what do neurotransmitters do

A

initiate a response by binding to their receptors at a synapse

35
Q

what are neurotransmitters receptors

A

ligand-gated ion channels

36
Q

what does the depolarisation of the plasma membrane as a result of the entry of positive ions trigger

A

the opening of voltage-gated sodium channels and further depolarisation occurs

37
Q

what is depolarisation

A

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

38
Q

what does inactivation of the sodium channels and the opening of potassium channels do

A

restores the resting membrane potential

39
Q

stages of restoring membrane potential

A

binding of a neurotransmitter triggers the opening of ligand-gated ion channels at a synapse.
ion movement occurs and there is depolarisation of the plasma membrane.
if sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage-gated sodium channels is triggered and sodium ions enter the cell done their electrochemical gradient.
this leads to a rapid and large change in the membrane potential.
a short time after opening, the sodium channels become inactivated.
voltage-gated potassium channels then open to allow potassium ions to move out of the cell to restore the resting membrane potential

40
Q

what does depolarisation of a patch of membrane cause

A

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

41
Q

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

A

it causes vesicles containing neurotransmitters to fuse with the membrane
this releases neurotransmitter which stimulates a response in a connecting cell

42
Q

what does restoration of the resting membrane potential allow

A

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

43
Q

how are ion concentration gradients re-established

A

by sodium-potassium pumps.

this actively transports excess ions in and out of the cell

44
Q

what follows depolarisation

A

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

45
Q

what is the retina

A

the area within the eye that detects light and contains two types of photoreceptor cells

46
Q

what are the types of photoreceptor cells that the retina contains

A

rods

cones

47
Q

what are rods

A

they function in dim light but do not allow colour perception

48
Q

what are cones

A

responsible for colour vision and only function in bright light

49
Q

what is the light-sensitive molecule retinal combines with

A

a membrane protein, opsin, to form the photoreceptors of the eye

50
Q

what is the retinal-opsin complex called in rod cells

A

rhodopsin

51
Q

what happens when retinal absorbs a photon of light

A

rhodopsin changes conformation to photoexcited rhodopsin

52
Q

what amplifies the signal

A

a cascade of proteins

53
Q

what does photoexcited rhodopsin activate

A

G-proteins called transducin, which activates the enzyme phosphodiesterase (PDE)

54
Q

how many molecules of G-protein does a single photoexcited rhosdopsin activate

A

a single photoexcited rhodopsin activated hundreds of molecules of G-protein.
each activated G-protein activates one more of PDE

55
Q

what does PDE catalyse

A

the hydrolysis of a molecule called cyclic GMP (cGMP)

56
Q

what does each active PDE molecule do

A

breaks down thousands of cGMP molecules per second

57
Q

what does the reduction in cGMP concentration affect

A

the reduction in cGMP concentration as a
result of its hydrolysis affects the function of
ion channels in the membrane of rod cells.

58
Q

what does the reduction in cGMP concentration result in

A

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

59
Q

what does a high degree of amplification result in

A

rod cells being able to respond to low intensities of light

60
Q

in cone cells, different forms of opsin combine with

A

retinal to give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, green, blue or UV

Advanced Higher Biology (15 decks)

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