Download Cell Signaling

Cell Communication
(Cell Signaling)
Cell-to-cell signaling:
• Important to both multicellular & unicellular organisms.
• Helps coordinate activities & events necessary for multicellular
organism to develop from zygote into billion of cells.
• Unicellular organisms - important in finding different mating
types for sexual reproduction.
• Example - Yeast cells have 2 mating types- “a cells” & “α (alpha)
cells”. Each type secretes a dif. chemical “factor” & each have
receptor sites for each others factors.
• These mating factors cause
the cells to grow toward one
another and bring about
other changes.
• Inside the cells there are a
series of chemical changes,
called the signal-transduction
pathway, that cause the
response.
• The new a/alpha cell has all
the genes from both the
different haploid yeast cells.
• These pathways are common
to both humans and yeast
cells suggesting that this
strategy evolved very early
on.
Which of the following is true about type a and type a
cells?
A) Only type a cells have receptor sites
B) Only type a cells have receptor sites
C) Only type a cells produce mating factors
D) Only type a cells produce mating factors
E) Both types of cells produce mating factors and has
receptors sites for the other’s mating factor
E
This is signaling between two different mating types of
yeast cells. Each one produces a mating factor for the
other and each one has a receptor site for the others
mating factor.
Cell Signaling in Bacteria Example: Quorum Sensing
• Bacteria cells secrete small molecules that are detected by other cells
• Concentration of signaling molecules causes bacteria to aggregate and
coordinate their behaviors
• Biofilm = an aggregation of bacterial cells to a surface
• Examples: Slimy coating on a fallen log, Coating on your teeth in
the morning
Which of the following provides the best evidence that
cell-signaling pathways evolved early in the history of life?
A) They are seen in "primitive" cells such as yeast.
B) Yeast cells signal each other for mating.
C) Signal transduction molecules found in distantly related
organisms are similar.
D) Signals can be sent long distances by cells.
E) Most signals are received by cell surface receptors.
C
If distantly related organisms have the same or closely
related proteins, that indicates that the biochemical
pathway has been around for a great deal of time. One
example of this is glycolysis.
Communication between cells can be:
1. Local signaling (very close)
Examples: Direct Contact
Paracrine Signaling
Synaptic Signaling
2. Long-Distance signaling (some distance away)
Examples: Endocrine (hormonal) signaling
Direct contact- Cells have cell junctions where direct contact of
the cytoplasms of adjacent cells occur. This allows for signaling
substances in the cytosol to pass freely between the adjacent cells.
Animals cells can communicate via direct contact between molecule
on their surface of their cell membranes. This is common in
embryonic development and the immune system (secretion of
interleukin when macrophage and virgin-T cell make a match).
• Paracrine signaling
• in animals
• Cell secretes a chemical
that acts on nearby
target cells.
• Example = Cells may
release a growth factor
that causes surrounding
cells to grow & multiply.
• Synaptic signaling
• Neurons secrete
neurotransmitters that
diffuse across an
intercellular space
(synapse) & interacts
with a another neuron.
Note - Local signaling in plants is not as well understood because
of the plant cell wall, plant must use a different
mechanism than those operating in animals.
This diagram is an example of
A) hormonal signaling
B) Paracrine signaling
C) long distance signaling
D) pheromonal signaling
B
The secretory cell and the receptor cells are close to one
another which makes this an example of paracrine
signaling.
Which of the following is the plant equivalent to gap
junctions?
A) tight junctions
B) desmosomes
C) receptor junctions
D) plasmodesmata
D
The plasmodesmata is analogous to the gap junctions found
in animal cells. They both allow for communication between
cells through the cytoplasm.
Long-distance signaling:
• Uses hormones (chemicals
secreted by one cell but exerts
effect on another cell some
distance away).
• In animals the hormone is
released into the vessels of
circulatory system and the
molecules travel to target
cells.
• In plant cells, hormones may
travel in vessels or diffuse into
the air as a gas.
• Hormones may vary in their
size and molecular structure.
Types of Animal Hormones:
1. Modified amino acids –
• ex. epinephrine is a modified tyrosine.
2. Proteins –
• ex. insulin is a large protein
3. Steroid Hormones –
• ex. testosterone and estrogen
4. Pheromones
• chemicals secreted by one animal to affect
the behavior of another animal.
This is an example of
A) hormonal signaling
B) paracrine signaling
C) short distance signaling
D) neuron signaling
A
This is a signal that travels through the blood stream some
distance away. That is the definition of hormonal
signaling. Paracrine signaling and neuron signaling is
signaling at close proximity.
The three stages of cell signaling are
1. Reception
2. Transduction
3. Response
1. Reception• begins with the signal interacting with a receptor
site located on the outside surface of the plasma
membrane
• Usually the signal is a ligand (a small molecule that
attaches to a large one).
• When the ligand attaches it causes a change in
shape of the receptor site.
• Receptors are usually proteins inserted into the
plasma membrane.
***Note ligands in cell communication can be hormones,
neurotransmitters, or growth factor, or something similar.
The correct sequence of events for this pathway is
A) reception->response -> transduction
B) reception->transduction->response
C) transduction->response->reception
D) transduction->reception->response
E) response->transduction->reception
B
The correct sequence of events is
1. reception
2. transduction (usually some sort of cascading pathway)
3. some sort of end response.
Three major types of membrane receptors are:
a. G-protein-linked receptors
b. tyrosine-kinase receptors
c. ion-channel receptors
a. G-protein-linked receptors vary in their binding sites
and for recognizing different G-proteins. Most have
seven alpha helices penetrating the plasma membrane.
When a G-protein-linked receptor binds with a signal or
ligand, it becomes activated and interacts with a Gprotein.
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