1.4 Communication and Signalling Flashcards Preview

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Flashcards in 1.4 Communication and Signalling Deck (60)
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1
Q

how do multicellular organisms signal between cells

A

using extracellular signalling molecules

2
Q

what are examples of extracellular signalling molecules

A

steroid hormones
peptide hormones
neurotransmitters

3
Q

what are receptor molecules of target cells

A

proteins with a binding for a specific signal molecule

4
Q

why does binding change the conformation of the receptor

A

initiates a response within the cell

5
Q

different cell types produce specific signals that can only

A

be detected and responded to by cells with the specific receptor

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

7
Q

in a multicellular organism, different cell types may show

A

a tissue-specific response to the same signal

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

9
Q

what are the receptors for hydrophobic molecules

A

transcription factors

10
Q

what are transcription factors

A

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

11
Q

what are examples of hydrophobic signalling molecules

A

steroid hormones
oestrogen
testosterone

12
Q

what do steroid hormones bind to

A

specific receptors in the cytosol or the nucleus

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

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

15
Q

what do hydrophilic signalling molecules bind to

A

transmembrane receptors and do not enter the cytosol

16
Q

what are examples of hydrophilic extracellular signalling molecules

A

peptide hormones

neuritransmitters

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

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

19
Q

what do transduced hydrophilic signals often involve

A

G-proteins or cascades of phosphorylation by kinase enzymes

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

21
Q

what do phosphorylation cascades allow

A

more than one intracellular signalling pathway to be activated

22
Q

what do phosphorylation cascades involve

A

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

23
Q

what can phosphorylation cascades result in

A

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

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

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