Unit 1 Cells and Proteins: Key Area 4 - Communication Within Multicellular Organisms Flashcards
(89 cards)
1
Q
How do multicellular organisms signal between cells?
A
Using extracellular signalling molecules.
2
Q
What are examples of extracellular signalling molecules used by multicellular organisms?
A
Steroid hormones, peptide hormones and neurotransmitters.
3
Q
How does communication occur in animals?
A
Through nerve transmissions and hormonal secretion.
4
Q
What is the nature of the signal of a nervous communication?
A
Electrical impulses and neurotransmitters.
5
Q
What is the transmission of the signal of a nervous communication?
A
Along neurons
6
Q
What is the target cell of a nervous communication?
A
Any cells with connections to neurons.
7
Q
What is the time for the response of a nervous communication?
A
Very fast
8
Q
What is the duration of the response of a nervous communication?
A
Transient.
9
Q
What is the extent of the response of a nervous communication?
A
Localised
10
Q
What is the nature of the signal of a hormonal communication?
A
Hormones
11
Q
What is the transmission of the signal of a hormonal communication?
A
Through the bloodstream.
12
Q
What is the target cell of a hormonal communication?
A
Almost any cell in the body.
13
Q
What is the time for response to occur of a hormonal communication?
A
Slow
14
Q
What is the duration of the response of a hormonal communication?
A
Long lasting
15
Q
What is the extent of the response of a hormonal communication?
A
Widespread
16
Q
What is the series of events in hormonal communication?
A
1) Signal molecule released from cell.
2) Signal molecule travels to target cell.
3) Signal molecule binds to receptor on target cell.
4) Binding causes conformational change.
5) This alters the response of the cell.
17
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.
18
Q
What does the binding of a signal molecule do to the receptor?
A
Binding changes the conformation of the receptor, which initiates a response within the cell.
19
Q
What do different cell types produce which are responded to by cells with the specific receptor?
A
Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor.
20
Q
How can signalling molecules have different effects on the different target cell types?
A
Signalling molecules may have different effects on the different target cell types due to differences in the intracellular signalling molecules an pathways that are involved.
21
Q
In a multicellular organism, what might different cell types show?
A
In a multicellular organism, different cell types may show a tissue-specific response to the same signal.
22
Q
How do hydrophobic signalling molecules work?
A
Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayers of membranes, and so bind to intracellular receptors.
23
Q
How do hydrophobic signals diffuse directly through the phospholipid bilayer?
A
They can do this because the tails of the phospholipids in the plasma membrane are also hydrophobic and allow the molecules to pass through.
24
Q
What are the receptors for hydrophobic signalling molecules?
A
Transcription Factors.
25
What are transcription factors and what can they do?
Transcription factors are proteins that when bound to DNA can either stimulate or inhibit transcription. They can enhance or block the binding of RNA polymerase to specific genes, therby controlling wether the gene is transcribed and therefore expressed.
26
what are examples of hydrophobic signals?
Thyroxine and Steroid Hormones.
27
What are facts about thyroxine?
- Produced by the thyroid
| - Regulates the rate of metaboilsm
28
What are steroid hormones that are examples of hydrophobic signalling?
Testosterone and Oestrogen
29
What do steroid hormones bind to?
Specific receptors in the cytosol or the nucleus forming a hormone - receptor complex.
30
where does the the hormone-receptor complex move to after the steroid hormone has bound to the specific receptor?
The nucleus where it binds to specific sites on DNA and affects gene expression.
31
What are the specific DNA sequences that the hormone - receptor complex binds to called?
Hormone Response Elements (HREs)
32
How does binding of steroid hormones at HREs affect transcription?
Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
33
How has oestrogen been found to influence transcription by binding to HREs?
Oestrogen has been found to influence the transcription of more than 80 different genes.
34
What is the pathway of how steroids effect transcription?
1) Steroid hormone passes through the plasma membrane into the nucleus.
2) The hormone binds to the receptor (transcription factor).
3) The hormone-receptor complex binds to specific sites on DNA (HREs).
4) Rate of transcription and gene expression is affected.
35
Where do hydrophilic signalling molecules bind to?
Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol.
36
What are examples of hydrophilic signals?
Peptide hormones and neurotransmitters.
37
Why do hydrophilic signalling molecules bind to transmembrane receptors?
They are not capable of passing across the hydrophobic plasma membrane.
38
What are the 3 steps and the basic description of each in the process of hydrophobic signalling molecules?
1) Reception - Signalling molecule binds to transmembrane receptor.
2) Transduction - Signal is passed through the cell.
3) Response - Will vary depending on the signal.
39
What do transmembrane receptors do in reception?
Transmembrane receptors change conformation (shape) when the ligand (hydrophilic signalling molecule) binds to the extracellular face; the signal molecule does not enter the cell, but the signal is transduced across the plasma membrane.
40
What do transmembrane receptors act as in reception?
Transmembrane receptors act as signal transducers by converting the extracellular ligand- binding event into intracellular signals, which alters the behaviour of the cell
41
What do transducer hydrophilic signals often involve?
1) G - Proteins
| 2) Cascades of phosphorylation by kinase enzyme.
42
What do G - proteins doin transduction?
G- Proteins relay signals from activated receptors (receptors that have bound to a signalling molecule) to target proteins such as enzymes and ion channels. Enzymes will then catalyse reactions within the cell. Ion channels will then either open or close to control ion movement.
43
What do cascades of phosphorylation do in transduction?
Phospholipid 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. Phosphorylation cascades allow more than one intracellular signalling pathway to be activated.
44
What are the 2 hormones involved in the control of blood glucose levels?
Insulin and Glucagon.
45
When is insulin made?
When there is an increase in blood glucose concentration.
46
Where is insulin made?
By cells in the pancreas.
47
Is insulin hydrophilic or hydrophobic?
Insulin is a hydrophilic peptide hormone.
48
What does insulin allow fat tissue and skeletal muscles to do?
Absorb glucose from the bloodstream.
49
What is the passage of glucose?
Glucose passes into the cells by travelling through a transporter protein called GLUT4 by facilitated diffusion.
50
What is the process of insulin binding?
1) Insulin binds to its receptors.
2) Receptor undergoes a conformational change that triggers phosphorylation of the receptor.
3) A phosphorylation cascade is started in the cell.
4) Vesicles containing GLUT4 are transported to the cell membrane.
5) Glucose passes through the GLUT4 transporters.
51
If there is a failure in insulin binding what will the person suffer from?
Diabetes
52
What is the cause and treatment of Type 1 diabetes?
- Caused by a failure to produce insulin in the pancreas.
| - Treated with regular injections of insulin throughout the day.
53
What is the cause and treatment of type 2 diabetes?
- Caused by a loss of insulin receptor function usually associated with obesity.
- May be treated with medication to lower blood glucose levels along with lifestyle changes e.g. consuming less sugar, increasing activity levels and losing weight.
- Exercise also triggers recruitment of GLUT4 so can improve the uptake of glucose to fat and muscle cells.
54
How is diabetes mellitus caused?
Diabetes mellitus can be caused by failure to produce insulin (type 1) or loss of receptor function (type 2)
55
What is the membrane potential?
All cells have a electrical potential difference (voltage) across their plasma membrane. This voltage is called the membrane potential. This is when there is a difference in electrical charge on the two sides of the membrane.
The minus sign means that the inside of the cell is negative relative to the outside.
56
What is the resting potential?
The membrane potential of a neuron that is not transmitting signal is called the resting potential.
57
What is the resting membrane potential?
Resting membrane potential is a state where there is no net flow of ions across the membrane.
58
At what potential difference is a neuron said to be not transmitting signals?
-60 and -8 mV ( millivolts).
59
What does the transmission of a nerve impulse require?
The transmission of a nerve impulse requires changes in the membrane potential of the neuron’s plasma membrane.
60
What is a nerve transmission?
A wave of depolarisation of the resting potential of a neuron.
61
What is depolarisation in terms of nerve transmission?
A change in the membrane potential to a less negative value inside.
62
If the change in membrane potential is large enough what might it trigger?
An action potential
63
What is an action potential?
An action potential is a wave of electrical excitation along a neuron’s plasma membrane.
64
What do neurotransmitters do in terms of the process of a nerve transmission?
Neurotransmitters initiate a response by binding to their receptors at a synapse.
65
After the neurotransmitter has bound to the receptor in the process of nerve transmission what happens?
A series of events occur which result in the depolarisation of the plasma membrane. The wave of depolarisation will then continue down the neuron, transmitting an electrical impulse.
66
After the transmission of an electrical impulse what happens in the process of nerve transmission in the sodium potassium pump?
The channel opens and positive sodium ions move in which causes depolarisation of the plasma membrane and the inside of the neuron becomes less negative. If sufficient ion movement occurs the membrane is depolarised beyond a threshold value, the opening of neighbouring voltage-gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient. Leading to a rapid and large change in the membrane potential.
67
What causes the restoration of the membrane potential?
The wave of depolarisation, caused by sodium ions entering the cell down their electrochemical gradient, continues down the neuron. A short time after the sodium channels become inactivated , which results in the voltage - gated potassium channels opening to allow potassium ions to move out of the cell. This results in the restoration of the resting membrane potential.
68
What happens when the action potential reaches the end of the neuron?
It causes vesicles containing neurotransmitters to fuse with the membrane - resulting in the release of neurotransmitter, which stimulates a response in a connecting cell.
69
What does the restoration of the resting membrane potential allow to happen?
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.
70
Following repolarisation what does the sodium potassium pump do.
Ion concentration gradients are re-established by the sodium-potassium pump, which actively transports excess ions in and out of the cell
71
What is the retina?
The retina is the area within the eye that detects light.
72
What are the 2 photoreceptor cells in the retina?
Rod and cone cells
73
What are rod cells sensitive to?
Changes in light intensity.
74
What are rod cells useful for?
Vision in areas of low light intensity.
75
As nocturnal animals have a greater proportion of rod cells what does this mean for the animals vision?
They have better vision at night.
76
Are cone cells sensitive to light?
No not as sensitive as rod cells.
77
What are cone cells particularly sensitive too?
Specific colours (wavelengths) of light: green, red and blue ( in some animals UV).
78
What do cone cells allow animals to have?
Colour vision
79
What do people who are colour blind lack?
A particular type of cone cell in their retina.
80
In animals what is combined to form the photoreceptors of the eye?
In animals the light-sensitive molecule retinal is combined with a membrane protein, opsin, to form the photoreceptors of the eye.
81
In rod cells,what is the retinal - opsin complex is callled?
Rhodopsin
82
In cone cells, different forms of opsin combine with retina; to give what?
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.
83
When retinal absorbs a photon of light what happens to rhodopsin?
Rhodopsin changes conformation to photoexcited rhodopsin.
84
What does retina response to light involve which amplifies the signal?
A cascade of proteins
85
What does photoexcited rhodopsin activate?
A G-protein called transducin, where a single molecule of photoexcited rhodopsin activates hundreds of molecules of G-protein.
86
What does transducin activate?
The enzyme phosphodiesterase, where each activated G-protein activates one molecule of PDE.
87
What does PDE catalyse?
The hydrolysis of a molecule called cyclic GMP (cGMP). Each active PDE molecule break down thousands of cGMP molecules per second.
88
What affect does the reduction in cGMP concentration as a result of its hydrolysis have?
The reduction in cGMP concentration as a result of its hydrolysis affects the function of the ion channels in the membrane of rod cells.
This results in the closure of ion channels in the membrane of the rod cells - inward leakage of positive (Na+) is halted so the membrane potential increases.
Hypertension (increasing charge) triggers more impulses in neurons in the retina.
89
What are the steps in retina response?
1) Retinal absorbs a photon of light and becomes photoexcited rhodopsin
2) Photoexcited rhodopsin activates G-protein (Transducin)
3) G-proteins activate phosphodiesterase (PDE)
4) PDE catalyses hydrolysis of cGMP
5) Concentration of cGMP decreases
6) Ion channels close – membrane potential increases
7) Nerve impulse is triggered in neurons in the retina
