Communication and Signalling Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

How do multicellular organisms signal between cells ?

A

-Multicellular organisms signal between cells using extracellular signalling molecules

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

-There are two main forms of communication; nervous and hormonal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are receptors ?

A

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

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Explain the specificity between signal and cells

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How can signals cause different responses ?

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.

-In a multicellular organism, different cell types may show a tissue-specific response to the same signal

Also links to specificity between signal and receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the two types of signalling molecules ?

A

1) Extracellular hydrophobic

2) Extracellular Hydrophilic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are examples of extracellular hydrophobic signalling molecules ?

A

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

-Steroid hormones bind to specific receptors in the cytosol or the nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are examples of extracellular hydrophilic signalling molecules ?

A

Peptide hormones (such as insulin) and neurotransmitters

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Explain hydrophobic signals and control of transcription

A

1) Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayers of membranes, and so bind to specific intracellular receptors, in the cytosol or the nucleus

2) The receptors for hydrophobic signalling molecules are transcription factors; proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.

3) The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression

4) The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression: The hormone-receptor complex binds to 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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why might not all cells respond to testosterone ?

A

-Testosterone is a steroid hormone, and an extracellular hydrophobic signalling molecule.

-All cells might not respond to testosterone as only target cells possess the appropriate regulatory proteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What do hydrophilic signalling molecules require to transmit a signal into a cell ?

A

Hydrophilic signalling molecules require receptor molecules at the surface of the cells because they are not capable of passing across the hydrophobic plasma membrane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe hydrophilic signal transduction ?

A

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

2) 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

3) Transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do G-proteins relay signals in a cell ?

A

G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.

-G-proteins possess quaternary structure (made of connected polypeptide subunits)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do phosphorylation cascades (phosphorylation cascades by kinase enzymes) relay a signal in a cell ?

A

-Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on.

-Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event; allow more than one intracellular signalling pathway to be activated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does insulin promote cell glucose uptake ?

A

Triggers recruitment of GLUT4 (does facilitated diffusion)

-Binding of the peptide hormone insulin (hydrophillic) to its receptor causes a conformational change which tirggers phosphorylation of the receptor. This causes an intracellular phosphorylation signalling cascade, which eventually leads to GLUT4-containing vesicles being transported to the cell membrane of fat and muscle cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What causes type 1 diabetes and how is it treated ?

A

-Diabetes mellitus can be caused by failure to produce insulin (type 1)

-Also known as insulin-dependent diabetes or juvenile diabetes

-Treated with regular insulin injections throughout the day

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What causes type 2 diabetes and how is it treated ?

A

-Diabetes mellitus can be caused by loss of insulin receptor function (type 2)

-Usually associated with obesity

-Also known as non-insulin-dependent diabetes

May be treated with;
-Medications to lower blood glucose
-Other lifestyle changes such as consuming less sugar and increasing activity levels.

Increasing exercise Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2. Also aids weight loss if necessary.

17
Q

What is the resting membrane potential ? (Nerve impulse)

A

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

The transmission of a nerve impulse requires changes in the membrane potential of the neuron’s plasma membrane.

18
Q

What is an action potential ?

A

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

19
Q

How is a nerve impulse transmitted ?

A

1) Neurotransmitters initiate a response by binding to their neurotransmitter receptors at a synapse, these receptors are ligand-gated ion channels, causing receptor to open and allowing positively charged Na+ to enter.

2) Binding of a neurotransmitter triggers the opening of ligand-gated ion channels at a synapse.

3) Ion movement occurs and there is depolarisation of the plasma membrane.

4) 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 (causing further depolarisation)

5) A short time after opening, the sodium channels become inactivated and voltage-gated potassium channels then open to allow potassium ions to move out of the cell to restore the resting membrane potential.

6) 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

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

8) 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

9) Following repolarisation the sodium and potassium ion concentration gradients are reduced. Ion concentration gradients are restored by the sodium-potassium pump, which actively transports excess ions in and out of the cell, back to resting potential levels

20
Q

What is depolarisation ?

A

Depolarisation is a change in the membrane potential to a less negative value inside.

21
Q

What restores the resting membrane potential ?

A

Inactivation of the sodium channels and the opening of potassium channels restores the resting membrane potential

22
Q

Describe the resting ion concentrations and charges inside and outside a cell

A

All cells have a higher concentration of Na+ outside the cell than inside, and a higher concentration of K+ inside the cell than outside.

The inside of the cell is relatively negative, and the outside is relatively positive.

23
Q

What part of the eye detects light ?

A

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

-The cells within the retina convert light into electrical signals

24
Q

What are rods and cones

A

Both are types of photoreceptor cells in the retina

-Rods function in dim light but do not allow colour perception, very sensitive to changes in light intensity.

-Cones are responsible for colour vision and only function in bright light, not as sensitive to light as rod cells but are particularly sensitive to particular colours and wavelengths of light (RGB) (In some animals, UV)

25
Q

What are the photoreceptors of the eye called ?

A

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

-In rod cells the retinal-opsin complex is called rhodopsin

26
Q

Describe the stages of initiation of a nerve impulse in the eye (to turn off rod cells)

A

1) Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin

2) A cascade of proteins amplifies the signal (allows vision in very low light levels, lets rods see)

3) Photoexcited rhodopsin activates a G-protein, called transducin, which activates the enzyme phosphodiesterase (PDE). A single photoexcited rhodopsin activates hundreds of molecules of G-protein. Each activated G-protein activates one molecule of PDE.

4) PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP) to GMP. Each active PDE molecule breaks down thousands of cGMP molecules per second. The sufficient reduction in cGMP concentration as a result of its hydrolysis affects the function of ion channels in the membrane of rod cells (low cGMP concentration turns off rods)

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

27
Q

What allows rods cells 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

28
Q

What allows cone cells in the retina to be able to detect colour ?

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

29
Q

Suggest ways in which a hydrophobic signalling molecule might have different effects in different tissues

A
  • Different tissues will have different responses to receptor binding.

-Different tissues will have different signal transduction pathways.

-Different genes switched on/off in different tissues

-There may be different hydrophobic signalling molecule receptors