Reactions between cells and how they communicate with each other/ interpret that message,
how it’s received and how the cell deals with it and makes several different messages. Must
interpret and create a cellular response. These are more positive outcomes. The foundation for
signal transduction and how it will lead us into the next topics. Will stay for the rest of the
Mechanisms how cells interpret their environment pick up on different types of molecules and
act upon them are mechanisms that are well conserved throughout evolution, between species,
different processes (I.e. making sure that organisms and cells can develop and defend against
pathogens or react against changes in their environment, etc.)
Smart Bio Videos: how cells respond and give off signals in the environment
-the message itself: what can we send from one cell to another to elicit a response? The
message must be received. If nothing receives that message or interacts with the message, it’s
going to be a chemical messenger and the cell will be oblivious to the message that is sent.
Once it is read, you must be able to understand, interpret it—deciding what the cell should do
and how it should respond to it. Sometimes, the message should be priority number one and
other times, it should be simply ignored and an entire gradient of responses between. The cell
must act upon what’s interpreted, and what is the best outcome. It should also act on the cell:
growing, dividing, dyeing, etc.
Neural activity involves transmission of information via ______; in contrast, endocrine activity
involves transmission information via _______?
A- Electrochemical evens; hormone transport to target tissues
B- Hormone transport; hormone release in body fluids
C- Electrical events; hormone transport through electrical signals
D- Hormone transport; hormone transport to target tissues
We do not transmit neural information through electricity, it is those fluctuations in the
electrochemical gradients, difference in flow of ions, how the action potential is sent down the
Communication between cells that was direct communication. Exchange of small ions, small
molecules from one cell to another (i.e. gap junctions)
- Signal transduction: to reach cells that are both near and far
o To be done quickly and efficiently
- There are different paths where this can be done
- Nature of the path depends on the physical properties of the chemical messengers
- Look at the paths and match the messengers that can be used for each of them The target tissues for steroids do not have receptors for them on the membrane surface,
A- Can enter the cell by facilitated diffusion
B- Alter the membrane potential of the cell, leading to cellular responses
C- Are soluble in the lipid bilayer
D- Are transported against their concentration gradient by active transporters in the cell
- Soluble; They’re able to freely diffuse and go across both layers of the membrane, so
they can find the receptors, the structures, proteins that can recognise the steroids,
bind to them and help the cell make the decision to make a cellular response. Will find
them in the cell—in the cytoplasm or in the nucleus. It’s true for lipophilic messengers.
6 Classes of chemical messengers.
- Steroids, lipids, peptides/proteins, purines, amines, gasses
- Steroids: lipophilic, derived from cholesterol, should be able to recognise a general
structure for steroids. Sorted into 3 classes – Based on the kinds of cellular classes
they’re responsible for i.e. sex hormones, glucocorticoids (cholesterol) and
mineralocorticoids—such as aldosterone, which helps regulate water and ions in
different tissues (i.e. salts, minerals and water content); they are lipophilic and cannot
package in vesicles, will be diffused across the membrane forming the vesicle—will be
used on demand to anchor and transport in hydrophilic environments, such as the
- Steroids vs. other chemical messengers
o Steroids enter the cell, which hydrophilic compounds never do and when bound
to receptors, the complex is immediately enabled as a transcription factor
(initiates the transcription of DNA to mRNA—proteins bind to sequences of the
DNA, and it activates or puts a stop of DNA to mRNA)
o When steroids bind to receptors, it forms a transcription factor
- Eicosanoids: from phospholipids—forms eracodonicacid and it is further modified of 1 of
2 enzymatic pathways, and could get one of 2 families of Eicosanoids—prostaglandins or
lupatrians(?), involved in inflammation and pain and they act locally. They are lipophilic
and act in an autocrine or paracrine pathway.
o Autocrine: cell secretes the messenger, to act upon it
o Paracrine: secretes the messenger, diffuses locally and act upon the
neighbouring cells. This is a very short distance
- - Peptides and proteins
o Proteins packaged in vesicle to be ready when cell wishes to secrete the
peptide/protein (i.e. glucagon, insulin, etc.)
o What proteins would you favour? Needs to be packaged in a vesicle. Needs to be
globular, soluble protein. These proteins will have catalytic or enzymatic activity.
Do not want to be active when packaged in vesicle—will package in an inactive form, additional process which prevents the activity from being turned on. Will
package the enzyme proteases that are responsible for cutting the peptide bond
and ridding the pro-sequence. When it’s released, the enzyme is activated,
cleaves the pro-portion and the enzyme is active.
o Will talk about protein synthesis, sorting, secretion in detail later.
▪ Need a group on these messengers
• Derived or biosynthesised from amino acids, r they are a.a.s
• Can package in vesicles
• When cell needs to secrete, it is already there—quick response in
relaying to next cell
• Often NTs
• Do have an exception, thyroid hormones are hydrophobic, cannot
package in vesicles, must be produced and secreted on demand
o Theobromine—found in chocolate and caffeine
▪ Caffeine exacerbates the effects of the stress hormone, cortisol!
o Derived from adenine or guanine
o Characteristic rings
o Direct communication and indirect communication
▪ Cannot travel far, have half-lives, however, they are essential…we survive
▪ They tend to passively diffuse across the membrane due to their size
▪ No need to have specific transport molecules and won’t need specific
receptors as they can act directly on their targets.
Cell must be