This is a comprehensive and detailed note on Chapter 7;Cell communication for Biol 105.
*Essential Study Material!!
*For you, at a price that's worth it!!
Ch 7: Cell Communication and Multicellularity
- intercellular signaling is a hallmark of multicellular organisms
- a cell’s response to a signal molecule takes place in 3 sequential steps:
o signal binds to receptor in the cell, often embedded outside cell membrane
o signal binding conveys a message to the cell
o cell changes activity in response to the signal
7.1 Cells Detect a Variety of Signals
- environmental variables are detected by individual cells, which undergo changes that
lead to responses
- to respond to a signal a cell MUST have a specific receptor that can detect and it AND a
way to use that info to influence cellular processes
- signal transduction pathway – series of biochemical steps whereby a stimulus to a cell
(hormone or neurotransmitter binding to a receptor) is translated into a response of the
cell
o vary greatly in details but essentially involves a signal, a receptor, and a response
Cells receive several types of signals
- physical signals (respond to light)
- chemical signals (odors and tastes)
- plants respond to light as a signal as well as an energy source
- cells deep inside multicellular organisms receive signals from neighboring cells and
surrounding extracellular fluids
- chemical signals in multicellular organisms are often made in one part of the body and
arrive at target cells by local diffusion or by circulation in the blood / plant vascular
system
- chemical signals are usually present in tiny concentrations (as low as 10^-10 M) and
differ in sources and mode of delivery
o autocrine: diffuse to (bind to) / affect the cells that make them
how tumor cells reproduce uncontrollably; make and respond to signals
that stimulate cell division
o juxtacrine: affect only cells right next to / in contact with the cell producing the
signal
common during development when cells are in groups and changing to
become specialized
o paracrine: diffuse to / affect nearby cells
inflammation when skin is cut
o hormones: signals that travel through circulatory systems of animals or vascular
system of plants
A signal transduction pathway involves a signal, a receptor, and responses
- for info from a signal to be transmitted to a cell, target cell must be able to receive the
signal and respond to it
, o job of receptors; only cells with the appropriate receptors can respond
o signal-receptor interaction sets off events inside the cell
- effects of signal transduction amplify signal’s effects; ultimate responses of cell /
organism may be short-term or long-term
- 1. signal arrives at a target cell
- 2. signal molecule binds to a receptor protein on the cell surface or inside the cell
- 3. signal binding changes the 3d shape of the receptor and exposes its active site
- 4. activated receptor activates a signal transduction pathway
- 5. signal transduction pathway activates a cell response
- short term changes = enzyme activation, cell movement
- long term changes = altered DNA transcription
- crosstalk – interactions between different signal transduction pathways; common,
pathways are often interconnected; can result in activation of one pathway and
inhibition of another
- multiple signal transduction pathways might converge on a single transcription factor,
allowing transcription of a gene to be adjusted in response to different signals
Under what conditions would autocrine signaling be most advantageous for a cell?
- Autocrine signaling would be important for a cell to maintain a specialized role. For
example, a cell might receive a signal to specialize and form a tissue of many cells. The
first cell would self-stimulate to grow and divide to form the tissue in response to self-
signaling.
How are hormones delivered to target cell receptors?
- Hormones are delivered to target-cell receptors through the circulatory system. In
animals, this is blood; in plants, it is the vascular system.
All cells have the potential to respond to all signals in an organism. What makes signaling
specific?
- Specificity for signal response occurs because only certain cells make the receptor for a
given signal.
Some cells can detect pH levels in their surroundings. How might a receptor detect changes in
pH?
- Changes in pH alter the ionization of R groups in amino acids. At an acidic pH, for
example, the concentration of H+ is high and amino acids with R groups containing –
COO- (e.g. glutamic acid) will be protonated: --COOH. This makes them uncharged and
less hydrophilic. In contrast, amino acids containing amine groups (--NH2, e.g., lysine)
will be protonated: --NH3+. This makes them charged and therefore strongly hydrophilic.
These changes may alter the 3d shape and function of the receptor.
7.2 Receptors Bind Signals to Initiate a Cellular Response
- receptor protein recognizes its signal specifically; specificity ensures only those cells that
make a specific receptor will respond to a given signal
, Receptors that recognize chemical signals have specific binding sites
- ligand – any molecule that binds to a receptor site of another (usually larger) molecule
- binding of the signaling ligand causes the receptor protein to change its 3d shape, which
initiates a cellular response
- ligand is usually not changed; it just “knocks on the door”
- sensitivity of a cell to a signal is determined by affinity of the cell’s receptors for signal
ligand (likelihood that receptor will bind to the ligand at any given concentration)
- R (receptors) + (bind to) L (ligands) RL
o binding is reversible
o for most ligand-receptor complexes (RL), binding is favored
- binding and dissociation processes have a rate constant; “[ ]” indicates concentration of
substance
o binding: R + L k1 RL
rate of binding = k1[R][L]
o dissociation: RL k2 R + L
rate of dissociation = k2[RL]
o when equilibrium is reached, the rate of binding equals the rate of dissociation
k1[R][L] = k2[RL]
[R][L] / [RL] = k2 / k1 = KD = dissociation constant
equilibrium constant measuring the tendency of 2 substances that
are bound together to separate into 2 smaller components; 2
substances are ligand and receptor
lower KD = higher affinity of ligand for receptor
some receptors have very low KD values, which allow binding
ligands at very low ligand concentrations
other receptors have higher KD values and need more ligand to be
present to set off signal transduction pathways
- drugs function as ligands that bind specific receptors; helpful to know specific receptor
the drug will bind to determine KD value of its binding
- when a ligand binds to receptors: change in receptor shape that may expose a previously
hidden amino acid group that participates in biochemical activity
o activity may be binding of another molecule, or a substrate for an enzyme
- other chemicals resembling it can bind to the receptor
o agonists – chemical substances (neurotransmitter) that elicits a specific response
in a cell or tissue; set a receptor into signal transduction mode as the ligand does
o antagonist – inhibitors that bind to the receptor and “freeze” it in place,
preventing the real ligand from binding, but do not set off signal transduction
Is the binding of adenosine and caffeine covalent or noncovalent?
- As with the binding of enzyme to substrate, the binding of caffeine and adenosine is
noncovalent. Both substances bind to a specific site on the receptor by their shape and
by interactions, including hydrophobic interactions (the rings).
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller anyiamgeorge19. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $9.99. You're not tied to anything after your purchase.
