VEA
Bringing Learning to Life
Program Support Notes
Senior Secondary
26mins
Cellular Signalling
Teacher Notes by Sue
Wright, B. Sc., Dip. Ed.
Produced by VEA Pty Ltd
Commissioning Editor Christine
Henderson B.Sc.
Ph.D. Dip.Ed.
Executive Producer Mark
McAuliffe Dip.Art (Film &
TV) Dip.Ed. B.Ed. Ph.D.
© VEA Pty. Ltd.
Suitable for:
Biology
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Cellular Signalling
For Teachers:
Brief Summary of Program
That certain cells produce certain substances under certain conditions is well known to Biology
students. What occurs inside the cell to translate a signal into a response is less often examined but of
growing importance to Biologists. This program explores the need for cellular signals, the nature of the
signals, how signals are transported to the cell and how different signals reach their extracellular and
intracellular receptors. It also examines what happens after the cell processes the signals by discussing
G-proteins, second messengers, activation of proteins and signalling cascades. Signal divergence and
convergence are also examined. The program uses graphics extensively to explain these complex
processes and many examples that will be familiar to senior secondary and early tertiary students.
DVD Timeline
00:00:00
00:04:16
00:04:51
00:08:06
00:08:24
00:14:27
00:14:59
00:20:06
00:20:40
00:23:56
00:24:20
00:25:07
00:25:36
Introducing Cellular Signalling
Summary
Types of Signalling Part 1
Summary
Types of Signalling Part 2
Summary
Signal Processing
Summary
Signal Amplification
Summary
Conclusion
Credits
Program end
Other Relevant Programs Available from VEA
Macromolecules 1 – Carbohydrates, Lipids & Nucleic Acids
Macromolecules 2 - Proteins & Proteomics
Cellular Signalling
Cell City Series
Acids and Bases
Bonding Between Molecules – Chemical Bonding Series
Please visit our website for many more relevant programs www.vea.com.au
VEA – Bringing Learning to Life
2
Cellular Signalling
For Students:
Before Viewing the Program
1.
What kinds of messages would a unicellular organism need to receive and process in order to
survive? What about the cells of a multicellular organism? What signals and processing is
required?
2.
What can you recall about the structure of the cell membrane? You could find this out by passing a
marker from one student to the next and having each student add to a diagram with a structure or
annotation. Consider what the chemical composition of the cell membrane is and the role of the
elements of the membrane.
3.
Define an enzyme. How do they work? Why is an enzyme specific to a substrate?
4.
What is the role of hormones? How are hormones transported from the cell that secretes them to
the cell that reacts to them? Are all hormones endocrine hormones? If not what other kinds of
hormones are there?
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Cellular Signalling
While Viewing the Program
1.
What had to evolve before multicellular existence could succeed?
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2.
What do unicellular organisms need to coordinate? What about cells in simple multicellular
organisms?
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3.
List the types of signal molecules.
_______________________________________________________________________________
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4.
What does successful signalling involve?
_______________________________________________________________________________
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5.
List the traditional biological receptors. How has the definition of a receptor been modified?
_______________________________________________________________________________
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6.
Define signal transduction.
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7.
What kinds of signalling molecules can pass directly across the cell membrane?
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8.
Why are carrier proteins necessary to carry some signals?
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Cellular Signalling
9.
What is paracrine signalling? How long do the signalling molecules last? What happens to them?
_______________________________________________________________________________
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10. What rapid signalling system has evolved to rapidly cover the long distances in large animals?
How does it work?
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11. What is endocrine signalling? How does its speed compare with that of synaptic signalling?
_______________________________________________________________________________
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12. What is autocrine signalling? What is its function?
_______________________________________________________________________________
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13. How do gap junctions work? What is an example of a situation where they are involved?
_______________________________________________________________________________
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Cellular Signalling
14. What happens to a cell deprived of all signals? How do you think this would be carried out?
_______________________________________________________________________________
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15. What two characteristics does a signalling molecule have to have to pass directly through a cell
membrane? What is an example of such a molecule?
_______________________________________________________________________________
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16. What are the effects of nitric oxide signals?
_______________________________________________________________________________
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17. List the steroid hormones? How do they signal a cell?
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18. What are steroid hormones synthesised from?
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19. Sometimes the steroid/ receptor complex causes the production of a protein which in turn causes
the production of another protein. What is this kind of response called?
_______________________________________________________________________________
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Cellular Signalling
20. Not all cells will have the same response to a steroid hormone. Give an example of this from the
program. Can you think of a further example?
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21. What is a signalling molecule released in response to prolonged low blood glucose? Where are its
target cells? What protein would these target cells produce in response to the signal?
_______________________________________________________________________________
_______________________________________________________________________________
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_______________________________________________________________________________
22. In what two ways does vitamin D act to increase calcium levels in the body?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
23. How do thyroid hormones which are insoluble in water, travel in the watery blood plasma?
_______________________________________________________________________________
24. Water soluble hormones can travel easily in the blood plasma but can’t cross the lipid bilayer that
makes up the cell membrane. How is this difficulty overcome?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
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Cellular Signalling
25. Complete the following table
Signal
Lifetime
Local mediators and neurotransmitters
Water soluble hormones
Steroids
Thyroid hormones
26. What opens a ligand gated channel? What opens a voltage gated channel?
_______________________________________________________________________________
_______________________________________________________________________________
27. What are three events that are regulated by ion channels?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
28. Where would you find a G-protein? What would it be coupled to? What concentrations can it
change?
_______________________________________________________________________________
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_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
29. Why are Calcium ions and cAMP called second messengers?
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Cellular Signalling
30. What are two examples of changes to proteins caused by phosphorylation?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
31. Calcium is an important second messenger in cells. Where is it mobilised from when it is required?
How does it get into the cytosol?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
32. How does calcium act directly to activate enzymes? What about indirectly? Where does it go when
it is no longer required?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
33. Complete the following table:
Molecule or structure
Number involved in signalling cascade
Rhodopsin molecules
Transducin molecules
Phosphodiesterase molecules
cAMP molecules
Sodium channels
Sodium ions
9
Cellular Signalling
34. What are the 2 hormones that target liver cells whose signals converge?
_______________________________________________________________________________
_______________________________________________________________________________
35. List the divergent responses of the neutrophil to the specific breakdown products of bacteria and
suggest why each one would be necessary.
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10
Cellular Signalling
After Viewing the Program
1.
Find out some more about programmed cell death. Where does it start? Why is it called
programmed? What is its role in the development of an embryo?
2.
What happens when the body has insufficient vitamin D? What happens when there is too much?
3.
Find out some more about the role of ion channels in the transmission of nerve impulses and in the
opening and closing of stomata.
4.
There is much in the media about the use of anabolic steroids. What are they? Who uses them?
Why are they harmful?
5.
Cellular signals are very important in the immune system. How does the body recognise self and
non-self? What happens when transplanted tissue is rejected? When there is an allergic reaction?
When there is an autoimmune disease?
6.
Adding phosphate to a protein is often how the activity of the protein is altered. Find out some
more about this.
11
Cellular Signalling
Suggested Student Responses
1.
What had to evolve before multicellular existence could succeed?
A signalling mechanism so that each cell knew its role
2.
What do unicellular organisms need to coordinate? What about cells in simple multicellular
organisms?
Aggregation for feeding and reproduction. Each cell needs to differentiate and divide in
synchrony with other cells of the organism for multicellular existence to succeed
3.
List the types of signal molecules.
Proteins, small peptides, amino acids, nucleotides, steroids, retinoids, fatty acid derivatives,
nitric oxide and carbon monoxide.
4.
What does successful signalling involve?
A sender, information being sent or a signal and a receiver or receptor.
5.
List the traditional biological receptors. How has the definition of a receptor been modified?
Photo, thermo, mechano and chemo receptors. The modified definition includes a molecule
that receives an extracellular message.
6.
Define signal transduction.
A process by which a cell converts an extracellular signal into a response.
7.
What kinds of signalling molecules can pass directly across the cell membrane?
Lipids or lipid soluble substances.
8.
Why are carrier proteins necessary to carry some signals?
Because many signals are insoluble in the watery blood plasma and tissue fluid so they need
to be carried to their target cell.
9.
What is paracrine signalling? How long do the signalling molecules last? What happens to them?
Short lived signals that are only taken up by neighbouring target cells. They only last a short
time after which they are destroyed by enzymes or immobilised.
10. What rapid signalling system has evolved to rapidly cover the long distances in large animals?
How does it work?
Synaptic signalling. Neurons allow electrical impulses to travel along axons. When this
impulse reaches the terminals at the end of the axon a chemical called a neurotransmitter is
released in the synapse and is picked up by a post-synaptic receptor
11. What is endocrine signalling? How does its speed compare with that of synaptic signalling?
Endocrine signals are molecules called hormones which are released into the blood stream of
an animal, or the sap of a plant, and are carried to the target cell. This is much slower than
synaptic signalling as it can only be as fast as sap or blood flow.
12. What is autocrine signalling? What is its function?
Autocrine signalling occurs when cells secrete signalling molecules that bind back to its own
receptors. Groups of identical cells use this type of signalling so that groups of identical cells
develop together.
13. How do gap junctions work? What is an example of a situation where they are involved?
Gap junctions are specialised cell-to-cell junctions that can form between closely opposed
plasma membranes directly connecting cytoplasm through water filled channels. Small
signalling molecules and ions called intracellular mediators, such as calcium ions and cyclic
AMP can pass through them, but macromolecules can’t do so.
Studies of embryos with water-soluble dyes show that embryo cells make and break these
connections in interesting patterns probably to coordinate the behaviour of cells.
12
Cellular Signalling
14. What happens to a cell deprived of all signals? How do you think this would be carried out?
These cells will activate a suicide program called programmed cell death. A programmed
series of enzyme activations would be responsible for this.
15. What two characteristics does a signalling molecule have to have to pass directly through a cell
membrane? What is an example of such a molecule?
The molecule needs to be small and hydrophobic. Nitric oxide is an example of such a
molecule.
16. What are the effects of nitric oxide signals?
It signals smooth muscle cells to relax and has long been used to treat angina which is heart
pain caused by not enough blood flow to heart muscle. Nitric oxide also activates
macrophages and neutrophils to kill invading micro-organisms.
17. List the steroid hormones? How do they signal a cell?
Steroid hormones include cortisol, the steroid sex hormones and vitamin D in vertebrates
and the moulting hormone in insects. They are able to pass through the plasma membrane
by diffusion and bind with an intracellular receptor. The receptor/ hormone complex can
pass through a nuclear pore into the nucleus where it interacts with DNA directly to alter the
rate of synthesis of a particular protein.
18. What are steroid hormones synthesized from?
Cholesterol
19. Sometimes the steroid/ receptor complex causes the production of a protein which in turn causes
the production of another protein. What is this kind of response called?
A delayed secondary response.
20. Not all cells will have the same response to a steroid hormone. Give an example of this from the
program. Can you think of a further example?
The steroid hormone testosterone causes the development of facial hair and also deepening of
the voice. There are many other examples such as oestrogen and secondary sexual
characteristics in females.
21. What is a signalling molecule released in response to prolonged low blood glucose? Where are its
target cells? What protein would these target cells produce in response to the signal?
The molecule is cortisol and its target cells are in the liver. The liver would produce glucagon
in response to this signal.
22. In what two ways does vitamin D act to increase calcium levels in the body?
It stimulates reabsorption of calcium in the kidneys and increases uptake of calcium in the
gut.
23. How do thyroid hormones which are insoluble in water, travel in the watery blood plasma?
They are carried by a carrier protein.
24. Water soluble hormones can travel easily in the blood plasma but can’t cross the lipid bilayer that
makes up the cell membrane. How is this difficulty overcome?
Water-soluble signalling molecules can’t pass through the cell membrane so they must be
detected by receptors on the cell surface. Their receptors, which are proteins, are found
embedded in the plasma membrane
25. Complete the following table
Signal
Local mediators and neurotransmitters
Water soluble hormones
Steroids
Thyroid hormones
Lifetime
Less than a second
Minutes
Hours
Days
13
Cellular Signalling
26. What opens a ligand gated channel? What opens a voltage gated channel?
A water soluble signalling molecule called a ligand. A change in membrane potential.
27. What are three events that are regulated by ion channels?
They are responsible for the excitation of muscle cells, are involved in mediating the
electrical signalling of nerve cells, are responsible for the leaf closing of Mimosa plants, allow
single celled Paramecium to reverse after a collision as well as being involved in regulating
stomatal aperture.
28. Where would you find a G-protein? What would it be coupled to? What concentrations can it
change?
G proteins are found coupled to receptors that have 7 transmembrane domains. It regulates
activity in the cell usually by changing the concentration of second messengers such as cyclic
AMP (cAMP) or calcium ions.
29. Why are Calcium ions and cAMP called second messengers?
The first messenger would be the G-protein and this effects the concentration of cAMP or
calcium ions so they are called second messengers.
30. What are two examples of changes to proteins caused by phosphorylation?
Phosphorylation of a channel protein can cause the channel to open. Phosphorylation of an
enzyme can activate it by opening its active site to allow substrate binding to occur...
31. Calcium is an important second messenger in cells. Where is it mobilised from when it is required?
How does it get into the cytosol?
Calcium is stored in E.R. and mitochondria. It can also come from outside the cell. Calcium
channels are opened to release intracellular and/ or extracellular Calcium when it is required
as a second messenger.
32. How does calcium act directly to activate enzymes? What about indirectly? Where does it go when
it is no longer required?
The concentration of calcium in the cell can directly regulate the activity of enzymes such as
protein kinases. Indirectly it can form a complex with an intra cellular Calcium receptor
called Calmodulin. The calcium/ calmodulin receptor activates different kinases. The
calcium can be rapidly removed from the cytosol back to membrane bound storage areas.
33. Complete the following table
Molecule or structure
Rhodopsin molecules
Transducin molecules
Phosphodiesterase molecules
cAMP molecules
Sodium channels
Sodium ions
Number involved in signalling cascade
1
500
500
100 000
250
1-10 million
34. What are the two hormones that target liver cells whose signals converge?
Adrenaline and glucagon.
35. List the divergent responses of the neutrophil to the specific breakdown products of bacteria and
suggest why each one would be necessary.
Changes in cell adhesion so cell can adhere to bacterial cells or toxins.
Changes in cell shape so that bacterial cells or toxins can be engulfed then broken down.
Changes in cell motility so that neutrophil can move where it is needed.
Increased oxygen uptake to allow for increased cellular respiration.
Release of hydrogen peroxide produced by increased cellular metabolism.
Release of proteases to breakdown bacterial protein.
14