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adv biology > 1.4 communication and signalling > Flashcards

1.4 communication and signalling Flashcards

1
Q

how do multicellular organisms achieve coordination and communication?

A

extracellular signalling molecules, receptors and responses

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2
Q

how does the binding of a signalling molecule change a receptor?

A

changes its conformation, altering/initiating the response in the cell

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3
Q

why can different cell types show a tissue-specific response to the same signal?

A

due to differences in intracellular pathways and signalling molecules

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4
Q

how do hydrophobic signals work?

A

by passing directly through phospholipid bilayers and binding to intracellular receptors

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5
Q

why can hydrophobic signals diffuse through the bilayer?

A

the tails of the phospholipids in the PM are also hydrophobic

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6
Q

how can hydrophobic signals influence the transcription of genes?

A

by binding to transcription factors

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7
Q

what are transcription factors?

A

a protein that when bound to DNA can either stimulate or inhibit transcription

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8
Q

name two steroid hormones

A

oestrogen and testosterone

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9
Q

what type of signalling molecules are oestrogen and testosterone?

A

hydrophobic

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10
Q

describe the process of a hydrophobic signalling molecule affecting transcription

A
  • the hormone binds to a receptor protein in the cytosol/nucleus
  • this forms a hormone/receptor complex
  • this binds to a specific DNA sequence called HREs
  • this influences the rate of transcription by affecting the expression of several different genes
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11
Q

what does HREs stand for?

A

hormone response elements

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12
Q

how do hydrophilic signals work?

A

signal molecules bind to proteins on the plasma membrane that act as receptors

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13
Q

name two examples of hydrophilic signal molecules

A

neurotransmitters and peptide hormones

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14
Q

how do transmembrane receptors proteins work?

A

they change conformation when the ligand binds to the extracellular face of the protein, triggering a transduction pathway

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15
Q

how does a signal transduction pathway work?

A

it links an extracellular chemical stimulus to a specific cellular response, altering the behaviour of the cell

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16
Q

what is a specific cellular response?

A

a cascade of biochemical reactions inside the cell that eventually reach the target molecule or reaction

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17
Q

an enzyme needs to be activated to bring out a response within the cell, but the receptor cannot directly interact with it. how is this resolved?

A

a G-protein is a relay protein which can relay the signal and activate the enzyme

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18
Q

what does the active G-protein do?

A

stimulates an enzyme, leading to a response in the cell

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19
Q

why is the response from a G-protein only temporary?

A

because the G protein also acts as a GTPase and hydrolysis the bound GTP to GDP, making the G protein inactive again

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20
Q

what is a phosphorylation cascade?

A

a series of events activated by one kinase, wich activates the next kinase etc

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21
Q

what do phosphorylation cascades result in?

A

the phosphorylation of many proteins from one original signal

22
Q

what happens when insulin, a peptide hormone, binds to its receptor?

A

change in conformation, which causes a phosphorylation cascade
this causes the recruitment of GLUT4 to the plasma membrane

23
Q

exercise can trigger GLUT4, therefore…

A

improving the uptake of glucose to fat in muscle cells in people with type 2 diabetes

24
Q

what is the resting potential?

A

the membrane potential of a neuron that is not transmitting signals

25
Q

what does it mean if a neuron is not transmitting signals?

A

there is no net flow of ions across the membrane

26
Q

what is an action potential?

A

a wave of electrical excitation along the PM of a neuron

27
Q

what does the transmission of a nerve impulse require?

A

the change of membrane potential to action potential

28
Q

what type of channel proteins are neurotransmitter receptors?

A

ligand-gated ion channels

29
Q

what occurs when neurotransmitters bind to their complementary receptors at a synapse?

A

depolarisation of the PM (the membrane potential becomes less -ve inside due to the entry of +ve ions)

30
Q

after the binding of neurotransmitters depolarises the plasma membrane, what does this change in voltage trigger?

A

the opening of voltage-gated sodium channels, resulting in further depolarisation

31
Q

what happens once the membrane becomes depolarised beyond a threshold?

A

sodium ions are able to enter down their electrochemical gradient, which results in a large change in membrane potential

32
Q

what happens when the channels become inactivated? (neurons)

A

voltage-gated potassium channels open, causing ions to move out which restores the resting membrane potential

33
Q

what happens once a patch of membrane has become depolarised?

A

neighbouring regions of the membrane go through the same cycle due to adjacent sodium channels opening

34
Q

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

A

it causes the vesicles containing the neurotransmitter to fuse with the membrane and release the chemical, stimulating a response in the connected cell

35
Q

how are ion concentration gradients re-established? (neuron)

A

by the Na/K pump as excess ions are actively transported either in or out

36
Q

what happens following repolarisation?

A

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

37
Q

what is the retina?

A

the area of the eye that detects light

38
Q

what are the two types of photoreceptor cell in the retina?

A

rods and cones

39
Q

describe rods

A

function in dim light, no colour perception

40
Q

describe cones

A

function in bright light, colour vision

41
Q

what is retinal?

A

a light-sensitive molecule found in the eye of animals

42
Q

how does retinal form photoreceptors?

A

by combining with a membrane protein called opsin

43
Q

what is retinal-opsin called in rod cells?

A

rhodopsin

44
Q

how does retinal become activated?

A

is absorbs a photon of light and changes conformation to become photoexcited rhodopsin

45
Q

describe the first step in the cascade of reactions occurring after the retinal becomes photoexcited

A

one photoexcited rhodopsin activates hundreds of G protein (transduction) molecules

46
Q

describe the second step in the cascade of reactions occurring after retinal becomes photoexcited

A

each G-protein activates one molecule of PDE (phosphodiesterase enzyme)

47
Q

describe the third step in the cascade of reactions occurring after retinal becomes photoexcited

A

PDE catalyses the hydrolysis of cyclic GMP (cGMP)

48
Q

how many cGMP molecules are broken down by 1 PDE per second?

A

thousands

49
Q

describe the fourth step in the cascade of reactions occurring after retinal becomes photoexcited

A

the decrease the cGMP concentration closes ion channels, triggering nerve impulses in the retina

50
Q

the greater the amplification of the impulse… (eye)

A

the better the rod cells are able to respond to low intensities of light

51
Q

what happens in cone cells?

A

different forms of opsin combine with retinal to give different receptor proteins. each of these proteins have a maximal sensitivity to specific wavelengths; red, green, blue or UV

adv biology (13 decks)

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