Key Area 4
(a) Coordination
In this section, we will learn about how extracellular signals can cause intracellular responses. This depends on the chemical nature of the extracellular signalling molecule, which, in turn, affects the way the response is triggered.
Just how is information transmitted throughout multicellular organisms?
Cell signalling and coordination is of fundamental importance to eukaryotic cell biology and whole research divisions are devoted to understanding how these pathways work. This true at the School of Life Science at the University of Dundee. Here, the MRC Phosphorylation and Ubiquitylation Unit studies phosphorylation and ubiquitylation pathways "to understand living creatures, and to change lives by helping to cure human disease". Click on the "Biology Coach" logo below to see the official video.
Task 55
Rachelle was well into her hormones. She'd personally had a lot of experience with them. "Aw right Miss, wit's this we're on tae the now?"
Dr McRobbie replied, "Rachelle, we are about to start a new section that essentially looks at hormonal and nervous communication throughout our bodies".
"Aye, gid one Miss - hormones chatting awa' tae each other like!"
"Hmm, sort of Rachelle, their method of communication is less sociable than that. Let's reflect first on what we already know about signalling. In our past studies, this has often followed the path of "Hormonal control" or "Nerve transmission". Produce a mindmap/spider diagram to illustrate what you already know about "communication in multicellular organisms".
"Och Miss, can we get the big pens oot then?"
Time to reflect back on your own learning. What can you recall about communication between cells?
Suggested responses are available here.
Signalling between cells
Multicellular organisms signal between cells using extracellular signalling molecules, which include steroid hormones, peptide hormones and neurotransmitters.
Steroid hormones
Steroid hormones, include cortisol, testosterone and oestrogen, are hydrophobic signalling molecules.
Peptide hormones
Peptide hormones include insulin, which is a hydrophilic signalling molecule.
Neurotransmitters
There are many types of neurotransmitters, including acetylcholine as shown above. This is a hydrophilic signalling molecule.
As shown in the diagram above, receptor molecules (shown as blue alpha helices) of target cells are proteins with a binding site for a specific signal molecule (shown in magenta).
The role of the receptor
From studies even at N5 level in Biology, we know that hormones, like insulin, travel in the bloodstream and then bind to a specific receptor. Upon binding its receptor, some response will take place.
We should also remember from N5 Biology that not all tissues will contain a receptor for insulin, for example. And, as a consequence, insulin affects some tissues and not others (see image below).
Task 56
"Aye, Miss, I remember you showed us that exact same picture in N5. Are you re-hashing ol' stuff for us here?"
Dr McRobbie slightly blushed at being caught out - they never let her away with anything!
"Fair enough Lilyjo, I think you've got me there. Anyhow, imagine you stumbled across this image in a textbook. What do you think the "legend" would say, describing the image? In your notes, add your own legend to explain what it shows".
Suggested responses are available here.
When this signal molecule binds to the receptor, the receptor changes conformation and this initiates a response within the cell.
As shown in the diagram opposite, this often involves a cascade of reactions (called a signal transduction pathway) that results in a cellular response.
In a multicellular organism, different cell types may show a tissue-specific response to the same signal.
This is due to differences in the intracellular signalling molecules and pathways (the signalling transduction pathway) that are involved. The image below highlights the tissue-specific response to insulin.
How do your hormones work?
Watch the TED Talk below before moving on for an excellent summary on how our hormones work.
Task 57
"Now, this is a wee bit tricky guys. Signalling is such an important part of every process that happens in our bodies. Things rarely happen in isolation. In degenerative diseases, quite often these signalling pathways start to break down and the final, desired cellular response no longer happens. Watch the video (from 31min 25s) about Parkinson's disease and read the information about the disease (below), along with your own research. Give a brief summary of the condition and explain how alterations to cell signalling lie at the heart of the physiological manifestations of the disease".
"Now. come oan Miss, that sounds like a lot o work tae me. Ye ken wit, we should do this in groups to lighten the load".
"Fair enough Big Davie, remember to pull your weight - I'll be checking".
Either in groups or individually, complete this task as well. Suggested responses are available here.
Copy of Dopamine_Parkinsons.pdf
Now go to SCHOLAR 4 and 4.1 on "Coordination" to consolidate your learning so far.
