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Advanced Higher Biology > UNIT 1 - communication and signalling > Flashcards

UNIT 1 - communication and signalling Flashcards

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1
Q

what are extracellular signalling molecules?

A

Steroid hormones, peptide hormones and neurotransmitters are examples of extracellular signalling molecules.

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2
Q

what are receptor molecules of target cells?

A

Receptor molecules of target cells are proteins with a binding site for a specific signal molecule

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3
Q

what effect does the binding of a signal molecule have on a receptor?

A

The binding of the signal molecules changes the conformation of the receptor, which initiates a response within the cell.

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4
Q

what do different cell types produce?

A

Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor.

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5
Q

what effect do signalling molecules have on different target molecules and what is this due to?

A

Signalling molecules may have different effects on different target cell types due to differences in the intracellular signalling molecules and pathways that are involved.

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6
Q

what happens with cells in multicellular organisms?

A

In a multicellular organism, different cell types may show a tissue-specific response to the same signal. they also show devisions of labour.

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7
Q

how are hydrophobic signalling molecules transported across the phospholipid bilayer?

A

Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayer of membranes, and so bind to intracellular receptors.

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8
Q

what are the receptors for hydrophobic signalling molecules known as?

A

The receptors for hydrophobic signalling molecules are transcription factors.

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9
Q

what are transcription factors?

A

Transcription factors are proteins that, when bound to DNA, can either stimulate or inhibit initiation of transcription

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10
Q

what are common examples of hydrophobic signalling molecules?

A

The steroid hormones oestrogen and testosterone are examples of hydrophobic signalling molecules.

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11
Q

what do steroid hormones bind to?

A

Steroid hormones bind to specific receptors in the cytosol or the nucleus to form a hormone-receptor complex

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12
Q

how does the hormone-receptor complex move?

A

The hormone-receptor complex moves from the cytosol to the nucleus, where it binds to specific sites on DNA and affects gene expression.

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13
Q

what is the hormone-receptor complex?

A

The hormone-receptor complex binds to specific DNA sequences called hormone response elements (HREs) and influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.

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14
Q

what do hydrophilic signalling molecules bind to and why?

A

Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol.

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15
Q

what are some examples of hydrophilic extracellular signalling molecules?

A

Peptide hormones and neurotransmitters are examples of hydrophilic extracellular signalling molecules. Acetylcholine, insulin.

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16
Q

how do transmembrane receptors work?

A

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

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17
Q

how do transmembrane receptors allow signal transduction?

A

by converting the extracellular ligand-binding event into intracellular signals that alter the behaviour of the cell.

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18
Q

what do transduced hydrophilic signals involve

A

Transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes

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19
Q

what is the function of G-protein?

A

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

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20
Q

what do phosphorylation cascades allow for?

A

Phosphorylation cascades allows more than one intracellular signalling pathway to be activated.

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21
Q

what are phosphorylation cascades?

A

Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on, resulting in the phosphorylation of many proteins as a result of the original signalling event.

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22
Q

what happens when insulin binds to its receptor?

A

The binding of insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor. This starts a phosphorylation cascade inside the cell, which eventually leads to GLUT4-containing vesicles are transported to the cell membrane.

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23
Q

what can diabetes type 1 and type 2 be caused by?

A 
Diabetes mellitus can be caused by a failure to produce insulin (type 1) or a loss of receptor
function (type 2).
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24
Q

why is exercise beneficial?

A

Exercise also triggers recruitment of GLUT 4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2 diabetes.

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25
Q

how does signalling occur?

A

1) signalling molecule released from cell
2) signalling molecule travels to target cell
3) signalling molecule binds to receptor on target cell
4) this causes a conformational change in the target cell
5) this alters the cells response

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26
Q

why do signalling molecules have different effects on different cells?

A

signalling molecules may have different effects on different target cell types due to difference in the intracellular signalling molecules and pathways that are involved

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27
Q

what are specific signals detected by?

A

different cell types produce specific signals which can only be detected and responded to by cells with the specific receptor

28
Q

what is the resting membrane potential?

A

The resting membrane potential is a state in which there is no net flow of ions across the membrane. This does not mean that ions are not flowing but instead the ions that are flowing out and exactly balanced by the ions flowing in

29
Q

what does the transmission of a nerve impulse require?

A

The transmission of a nerve impulse requires changes in the membrane potential of the neurons plasma membrane.

30
Q

what is an action potential?

A

An action potential is a wave of electrical excitation along a neuron’s plasma membrane.

31
Q

how do neurotransmitters create a response?

A

Neurotransmitters initiate a response by binding to their receptors at a synapse.

32
Q

what are neurotransmitter receptors also known as?

A

Neurotransmitter receptors are ligand-gated ion channels that open when a neurotransmitter binds.

33
Q

what is depolarisation?

A

Depolarisation is a change in the membrane potential to a less negative value inside as positive ions enter.

34
Q

what can sufficient ion movement cause?

A

If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value which triggers the opening of voltage-gated sodium channels and more sodium ions enter the cell down their electrochemical gradient resulting in further depolarisation.

35
Q

what is action potential caused by?

A

it is caused by the depolarisation of the resting potential

36
Q

what happens during the depolarisation of a patch of membranes?

A

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

37
Q

how is an action potential triggered?

A

Neurotransmitters initiate a response by binding to their receptors at a synapse.

Neurotransmitter receptors are ligand-gated ion channels

After binding to the receptor, there is a change in conformation in the receptor/channel

The channel opens and Na+ ions diffuse through

If enough diffuses through, the voltage changes across the membrane and a patch of membrane is depolarised

Nearby voltage-gated Na+ ion channels now open

More Na+ ions diffuse into the cell down the electrochemical gradient

This depolarises more patches of the membrane in the same region (like dominos knocking each other over)

The effect travels along the length of the neurone, leading to a wave of depolarisation i.e. an action potential

At the end of the neurone, vesicles release neurotransmitters into the next synapse

38
Q

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

A

When the action potential reaches the end of the neuron it causes vesicles containing neurotransmitters to fuse with the membrane; this releases the neurotransmitter, which stimulates a response in a connecting cell.

39
Q

what happens when the resting membrane potential is restored?

A

Restoration of the resting membrane potential 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.

40
Q

how is ion concentration re-established?

A

Ion concentration gradients are re-established by the sodium-potassium pump, which actively transports excess ions in and out of the cell.

41
Q

what happens after repolarisation?

A

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

42
Q

what is the retina and what is its function?

A

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

43
Q

function of rod and cone cells?

A

Rods function in dim light but do not allow colour perception. Cones are responsible for colour vision and only function in bright light.

44
Q

what is responsible for photoreceptors in animals?

A

In animals the light-sensitive molecule retinal is combined with a membrane protein, opsin, to form the photoreceptors of the eye. (retinal-opsin complex)

45
Q

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

A

In rod cells the retinal-opsin complex is called rhodopsin

46
Q

how does retinal work?

A

Retinal absorbs a photon of light and rhodopsin changes conformation to photo-excited rhodopsin, which starts a cascade of proteins amplifying the signal.

47
Q

what does photo-excited rhodopsin do?

A

Single photoexcited rhodopsin activates hundreds of G-proteins called transducins, which activate a single molecule of the enzyme phosphodiesterase (PDE) each.

48
Q

what does PDE do?

A

PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP) Each active PDE molecule breaks down thousands of cGMP molecules per second..

49
Q

what happens due to the reduction of cGMP concentration due to hydrolysis？

A

The reduction in cGMP concentration affects the function of ion channels in the membrane of rod cells, which close ion channels and trigger nerve impulses in neurons in the retina.

50
Q

what happens in rod cells to allow them to be able to respond to low intensities of light?

A

A very high degree of amplification results in rod cells being able to respond to low intensities of light.

51
Q

what do different forms of opsin combine with retinal to produce in cone cells?

A

In cone cells, different forms of opsin combine with retinal to give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, green, blue or UV.

52
Q

what is the action potential?

A

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

53
Q

what are cones?

A

photoreceptor cells responsible for colour vision; they only function in bright light

54
Q

what is cyclic GMP?

A

a second messenger for visual transduction; it is present in high concentrations in photoreceptor cells

55
Q

what are GLUT4 glucose transporter proteins?

A

the insulin-regulated glucose transporter, insulin triggers the movement of GLUT4 transporters to the membrane surface, increasing uptake of glucose to be converted to glycogen

56
Q

what are G-proteins?

A

also known as guanine nucleotide-binding proteins; a family of proteins that act as molecular switches inside cells, which are involved in transmitting signals from a variety of stimuli outside a cell to its interior

57
Q

what are Hormone response elements (HREs)?

A

a short sequence of DNA within the promoter of a gene that are able to bind to a specific hormone-receptor complex and therefore regulate transcription

58
Q

what is the hormone receptor complex?

A

formed when steroid hormones bind to specific receptors in the cytosol or the nucleus; they bind to specific sites on DNA and affect gene expression

59
Q

what is the ion concentration gardient?

A

gradients created by ion pump enzymes that transport ionic solutes across the membrane; energy is required to produce a gradient, so the gradient is a form of stored energy

60
Q

what is opsin?

A

a light-sensitive protein molecule found in the animal kingdom

61
Q

Phosphodiesterase (PDE)

A

an enzyme that catalyses the hydrolysis of cyclic GMP (GMP)

62
Q

what are photoreceptor cells?

A

cells (rods and cones) found in the retina that are capable of visual phototransduction (converting light - visible electromagnetic radiation - into electrical signals)

63
Q

what is repolarisation?

A

the restoration of a membrane potential following depolarisation (that is, restoring a negative internal charge)

64
Q

what is the retinal?

A

a light-sensitive molecule within the eye that binds with opsin to form photoreceptors in the eye

65
Q

Rhodopsin

A

the retinal-opsin complex in rod cells

66
Q

what are rods?

A

photoreceptor cells in the retina that function in dim light and respond to low light intensities; they do not allow colour perception

Advanced Higher Biology (11 decks)

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