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Advanced Higher Biology 2025 > KA1.4 - Communication and Signalling > Flashcards

KA1.4 - Communication and Signalling Flashcards

Unit 1 (65 cards)

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1
Q

Why do multicellular organisms use extracellular signalling molecules?

A

To signal between cells.

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2
Q

Give 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 site for a specific signal molecule

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4
Q

What happens when a signal molecule binds to a receptor?

A

Binding changes the conformation of the receptor, which initiates a response within the cell.

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5
Q

Why can specific signals only be detected and responded to by certain cells?

A

Different cell types only possess the specific receptor required to detect and respond to that signal.

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6
Q

Why might a signalling molecule have different effects on different target cell types?

A

Due to differences in the intracellular signalling molecules and pathways involved in those specific cell types, leading to a tissue-specific response.

Pressing the ‘button’ does different things in different cells

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7
Q

How do hydrophobic signalling molecules pass through cell membranes?

A

They can diffuse directly through the phospholipid bilayers.

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8
Q

Why can hydrophobic signalling molecules diffuse directly through the phospholipid bilayer?

A

The hydrophobic tails of the phospholipids in the plasma membrane allow the hydrophobic molecules to pass across.

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9
Q

What direct influence can hydrophobic signals have within a cell?

A

They can directly influence the transcription of genes.

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10
Q

What type of proteins are the receptors for hydrophobic signalling molecules?

A

Transcription factors

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11
Q

Define a ‘transcription factor’

A

Proteins that, when bound to DNA, can either stimulate or inhibit the initiation of gene transcription.

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12
Q

Give examples of steroid hormones.

A

Oestrogen and testosterone.

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13
Q

What are steroid hormones an example of?

A

Hydrophobic signalling molecule

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14
Q

Where do steroid hormones bind to their specific receptors?

A

In the cytosol or in the nucleus

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15
Q

What happens after a steroid hormone binds to its receptor to form a hormone-receptor complex?

A

The complex moves to the nucleus where it binds to specific sites on DNA called hormone response elements (HREs), influencing the rate of transcription of many different genes.

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16
Q

When a steroid hormones binds to it’s receptor it forms what?

A

Hormone-receptor complex

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17
Q

Why can’t hydrophilic extracellular signalling molecules enter the cell’s cytosol?

A

They cannot diffuse directly through the phospholipid bilayers of membranes.

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18
Q

What do hydrophilic extracellular signalling molecules bind to initiate a response?

A

Transmembrane receptors

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19
Q

What happens to a transmembrane receptor when its specific ligand (signal molecule) binds to its extracellular face?

A

It changes conformation

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20
Q

How do transmembrane receptors act as signal transducers?

A

By converting the extracellular ligand-binding event into intracellular signals, which then alters the behaviour of the cell

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21
Q

What molecular mechanisms often occur following the transduction of hydrophilic signals?

A

Involve G-proteins or cascades of phosphorylation by kinase enzymes.

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22
Q

Give two examples of hydrophilic extracellular signalling molecules.

A
  • Peptide hormones
  • Neurotransmitters
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23
Q

Which type of signalling molecule crosses the cell membrane, and which does not?

A
  • Crosses: Hydrophobic signalling molecule
  • Does not cross: Hydrophilic signalling molecule
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24
Q

Which type of signalling molecule binds to intracellular receptors?

A

Hydrophobic signalling molecule

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25
Which type of signalling molecule forms receptor/signal molecule complexes, binds to HREs on DNA, and can directly affect gene expression?
Hydrophobic signalling molecule
26
Which type of signalling molecule can activate G-protein cascades and/or phosphorylation cascades?
Hydrophilic signalling molecule
27
What is the role of G-proteins in signal transduction?
They relay signals from activated receptors (that have bound to a signalling molecule) to target proteins such as enzymes and ion channel | They start the signal transduction process
28
What is the main benefit of phosphorylation cascades in intracellular signalling?
They allow more than one intracellular signalling pathway to be activated from a single activated transmembrane receptor.
29
Briefly describe how a phosphorylation cascade works.
A series of events where one kinase activates the next in sequence, leading to the phosphorylation of many proteins as a result of the original signalling event.
30
What type of signalling molecule is insulin?
It is a **peptide** hormone (a hydrophilic signalling molecule)
31
What is the purpose of insulin?
Involved in the homeostatic control of blood glucose concentration.
32
What happens when insulin binds to its receptor on fat and muscle cells?
This binding causes a conformational change that triggers phosphorylation of the receptor.
33
What is the key outcome of the intracellular signalling cascade initiated by insulin binding and receptor phosphorylation?
It triggers the recruitment of GLUT4 glucose transport proteins to the cell membrane of fat and muscle cells.
34
What is the result of GLUT4 glucose transport proteins being recruited to the cell membrane?
This will increase the passive transport of glucose from the bloodstream into the cell.
35
What are the two main causes of Diabetes Mellitus?
1. Failure to produce insulin (Type 1) 1. Loss of receptor function (Type 2)
36
What is Type 2 Diabetes generally associated with?
Obesity
37
How can exercise help improve glucose uptake in subjects with Type 2 Diabetes?
Exercise triggers the recruitment of GLUT4 transport proteins, which improves the uptake of glucose into fat and muscle cells.
38
What is the resting membrane potential of a neuron?
A state where there is no net flow of ions across the neuron's plasma membrane, typically around -70 mV.
39
How is the resting membrane potential in neurons primarily generated and maintained?
By the action of the Na+/K+ pump, which removes 3 positive sodium ions from the cell and allows 2 positive potassium ions into the cell.
40
What specific change in the neuron's membrane potential is required for the transmission of a nerve impulse?
An action potential
41
Define 'action potential'
A wave of electrical excitation that travels along the neuron's plasma membrane.
42
Describe **Step 1** of nerve transmission between neurons
The action potential causes neurotransmitters to be released initiating a response by binding to their receptors at a synapse. | AP arrives at presynaptic neuron and NT binding on post-synaptic side
43
Describe **Step 2** of nerve transmission between neurons
Neurotransmitter receptors are ligand-gated ion channels; following binding of the neurotransmitter the ion channel opens and positively-charged ions flood into the cell.
44
Describe **Step 3** of nerve transmission between neurons
The influx of positive ions depolarises the plasma membrane.
45
Define 'depolarisation'
Depolarisation is a change in the membrane potential to a **less** **negative** value inside the cell, compared to outside and often approached ~0mV at this stage.
46
Describe **Step 4** of nerve transmission between neurons
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 down their electrochemical gradient. This leads to a rapid and large change in the membrane potential (increasing to between 0mV and +70mV).
47
Describe **Step 5** of nerve transmission between neurons
A short time after opening, the sodium channels become inactivated. Voltage-gated potassium channels then open to allow potassium to move out of the cell. This removes positive charges from the inside of the cell and starts to bring the resting potential closer to resting values of approx. -70mV.
48
What fully restores the resting membrane potential (to around -70mV) after nerve cell transmission?
The sodium-potassium pump, which actively transports excess ions in and out of the cell.
49
What does the full restoration of the resting membrane potential allow for the voltage-gated sodium channels?
It allows them to return to a conformation that permits them to open again in response to a new depolarisation.
50
What happens to the voltage-gated sodium channels a short time after they open during an action potential?
They become inactivated. | Step 5
51
What happens if the membrane depolarises beyond a threshold value, leading to a rapid and large change in membrane potential?
The opening of voltage-gated sodium channels is triggered, and sodium ions enter the cell down their electrochemical gradient. | Step 4
52
How does an action potential travel along a neuron's axon?
By using waves of depolarisation: depolarisation of one patch of membrane causes neighbouring regions to depolarise and go through the same cycle as adjacent voltage-gated sodium channels are opened.
53
What two types of photoreceptor cells are found in the retina of the eye?
Cones and Rods
54
What two molecules combine to form the photoreceptors of the eye in animals?
The light-sensitive molecule retinal combined with a membrane protein, opsin. | Found in both cones and rods
55
What is the function of rods?
They function in dim light but do not allow colour perception.
56
What is the specific retinal-opsin complex found in rod cells?
Rhodopsin
57
What is **Step 1** in the light detection process in rod cells?
Retinal absorbs a photon of light, causing rhodopsin to change conformation to photoexcited rhodopsin.
58
What is **Step 2** in the light detection process in rod cells?
A cascade of proteins amplifies the signal.
59
What is **Step 3** in the light detection process in rod cells?
Photoexcited rhodopsin activates a G-protein, called transducin, which activates the enzyme phosphodiesterase (PDE).
60
What is **Step 4** in the light detection process in rod cells?
PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP)
61
What is **Step 5** in the light detection process in rod cells?
This results in the closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina.
62
Why do rod cell have a high degree of signal amplification?
A single photoexcited rhodopsin activates hundreds of transducin G-proteins, each activating many PDEs, and each active PDE breaks down thousands of cGMP molecules per second.
63
What is the impact of the signal amplification seen in rod cells?
Allows rod cells to respond to low intensities of light.
64
What are cones responsible for, and in what light conditions do they function?
Responsible for colour vision and only function in bright light.
65
How do cones provide colour vision?
Different forms of opsin combine with retinal to give distinct photoreceptor proteins, each with maximal sensitivity to specific wavelengths (e.g., red, green, blue).

Advanced Higher Biology 2025 (19 decks)

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