Unit 4: Cell Communication and Cell Cycle
What’s the big deal?
Cells must use energy and information transmission to communicate and replicate
Pages 1-3 are meant to help highlight the important information included in each unit. While this can be a major source of
information, make sure to use any/all studying tools available to you (ie class notes, textbook, videos, supplemental study books,
etc.) Please note that while the College Board lays out the topics in this order, the class may go through the topics in a different
order or combine similar topics.
Topic 1: Cell Communication
Learning Objective
IST-3.A: Describe the ways that cells can communicate with
one another.
IST-3.B: Explain how cells communicate with one another
over short and long distances.
Essential Knowledge
IST-3.A.1: Cells communicate with one another through
direct contact with other cells or from a distance via
chemical signaling—
a. Cells communicate by cell-to-cell contact
IST-3.B.1: Cells communicate over short distances by using
local regulators that target cells in the vicinity of the
signal-emitting cell—
a. Signals released by one cell type can travel long
distances to target cells of another cell type.
Vocabulary/Review Questions
Direct contact Gap junctions
Plasmodesmata
hormones
1. Fill in the blanks: In direct contact communication,
animal cells communicate through _______ junctions
and plant cells communicate through _________.
2. What do animals and plants use for long distance
signaling? Differentiate between animals and plants
when they use this to communicate.
3. Differentiate between paracrine signaling and synaptic
signaling.
4. True or false: insulin signaling is an example of local
signaling.
Topic 2: Introduction to Signal Transduction
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Learning Objective
IST-3.C: Describe the components of a signal transduction
pathway.
IST-3.D: Describe the role of components of a signal
transduction pathway in producing a cellular response.
Essential Knowledge
IST-3.C.1: Signal transduction pathways link signal
reception with cellular responses.
IST-3.C.2: Many signal transduction pathways include protein
modification and phosphorylation cascades.
IST-3.D.1: Signaling begins with the recognition of a chemical
messenger—a ligand—by a receptor protein in a target cell—
a. The ligand-binding domain of a receptor recognizes a
specific chemical messenger, which can be a peptide, a
small chemical, or protein, in a specific one-to-one
relationship.
b. G protein-coupled receptors are an example of a receptor
protein in eukaryotes.
IST-3.D.2: Signaling cascades relay signals from receptors to
cell targets, often amplifying the incoming signals, resulting in
the appropriate responses by the cell, which could include cell
growth, secretion of molecules, or gene expression—
a. After the ligand binds, the intracellular domain of a
receptor protein changes shape, initiating transduction of
the signal.
b. Second messengers (such as cyclic AMP) are molecules
that relay and amplify the intracellular signal.
c. Binding of ligand-to-ligand-gated channels can cause the
channel to open or close.
Vocabulary/Review Questions
Reception
Transduction
Second
messengers
Protein
phosphatase
GPCR
cAMP
Receptor
Ligand
Ligand-gated Protein kinase
ion channel
Response
1. Summarize the three stages of cell signaling in one
sentence each.
2. If you were given a problem on the AP exam that
described a water-soluble (polar) receptor, where would it
be located in the cell?
3. Receptors that bind to estrogen, a hormone would be
found where in the cell?
4. What do second messengers do, and why is this role so
important in some cells?
5. Differentiate between the role of protein kinase and
protein phosphatase in cells.
6. What does the term “signal” refer to in a signal
transduction cascade?
7. Neurons can participate in both local and long distance
signaling. How is this possible? (you may do research
online to help answer this question if needed)
8. How are signals passed from outside of the cell to inside
of the cell?
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Topic 3: Signal Transduction
Learning Objective
IST-3.E: Describe the role of the environment in eliciting a
cellular response.
IST-3.F: Describe the different types of cellular responses
elicited by a signal transduction pathway.
Essential Knowledge
IST-3.E.1: Signal transduction pathways influence how the
cell responds to its environment.
IST-3.F.1: Signal transduction may result in changes in gene
expression and cell function, which may alter phenotype or
result in programmed cell death (apoptosis).
1.
2.
3.
4.
5.
Vocabulary/Review Questions
Describe the “response” that a cell can have to a signal.
How is it possible that a single signal molecule can elicit
massive cellular responses?
What is transcription and translation (as it pertains to
DNA)?
True or false: the final molecule in a signal transduction
pathway can act as a transcription factor, meaning that it
can turn genes off or on.
What does it mean if a gene is turned off vs on?.
Topic 4: Changes in Signal Transduction Pathways
Learning Objective
IST-3.G: Explain how a change in the structure of any
signaling molecule affects the activity of the signaling
pathway
2.
3.
4.
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Essential Knowledge
IST-3.G.1: Changes in signal transduction pathways can alter
cellular response—
a. Mutations in any domain of the receptor protein or in
any component of the signaling pathway may affect the
downstream components by altering the subsequent
transduction of the signal.
IST-3.G.2: Chemicals that interfere with any component of
the signaling pathway may activate or inhibit the pathway.
1.
Vocabulary/Review Questions
What would happen to the signal transduction pathway if
protein phosphatase was mutated?
What would happen to the signal transduction pathway if
protein kinase was mutated?
If a receptor protein is mutated, can it receive a ligand?
Why or why not?
How can chemicals activate or inhibit a pathway? (i.e
what does “activate” mean and what does “inhibit” mean
in terms of a signaling cascade?)
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Topics 1, 2, 3, and 4
Cell Communication
Cell-to-cell communication is critical for the ___________________ and _____________________ of cells.
Responsible for:
How Do Cells Communicate?
Cells communicate through three general ways
1.
2.
3.
Direct Contact
Direct contact:
Signaling substances and other material dissolved in the cytoplasm can pass ___________________
between ______________________ cells.
Animal cells:
Plant cells:
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Example: Immune cells
➔ Questions?
➔ Textbook
chapters/pages
to review
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Local Regulators
Local regulators:
The chemical messages will cause a ______________________ in a ______________________ cell.
Examples:
Paracrine signaling:
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Synaptic signaling:
➔ Questions?
➔ Textbook
chapters/pages
to review
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Long Distance Signaling
Animals and plants use ___________________________ for long distance signaling.
Plants:
Animals:
Example:
Insulin
Quick Check:
1. What type of communication involves a cell secreting a substance to an adjacent target cell?
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2. Plant cells in direct contact with each other can diffuse substances through these structures to
communicate. What are they?
➔ Questions?
➔ Textbook
chapters/pages
to review
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Practice Problems: Modes of Cell Communication
Directions: Identify the type of signaling that each example best represents: direct contact (via gap junctions or
plasmodesmata), local signaling (paracrine or synaptic), or long-distance signaling .
1. Embryonic stem cells are of great interest to researchers as they are
pluripotent, meaning they can become many different cell types as they
grow and differentiate. So how do embryonic stem cells “know” what
cell to become? Researchers have discovered embryonic stem cell
markers, which are molecules expressed on the surface of the cells that
interact and signal to adjacent cells through channels comprised of the
protein connexin.
2. The thyroid is a butterfly shaped gland located on the front side of the
neck. The thyroid produces three main hormones: triiodothyronine,
tetraiodothyronine, and calcitonin. These thyroid hormones can
generate signaling pathways that lead to the cell proliferation and
regulation of metabolic activity.
3. Meningothelial cells (MECs) play a vital role in regulating homeostasis
of spinal fluid. MECs are connected via tight junctions, gap junctions,
and aquaporins in order to communicate with adjacent cells.
4. During physical activity, heart rate increases. Endothelial cells in the
body sense the increased heart rate and release nitric oxide. Nitric oxide
relaxes nearby smooth muscle, which means blood vessels expand
allowing for increased blood flow through the body.
5. In order for a muscle contraction to occur, nerve cells must signal to
muscle cells. Motor nerves that signal to skeletal muscles release
acetylcholine, which will bind to nicotinic acetylcholine receptors on
skeletal muscles and cause a contraction.
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6. Auxins are a group of plant hormones that play vital roles in mediating
growth and development. Auxin is transported through plant tissue by
passive diffusion. A recent study revealed that as the root tips of plants
grow, there is an influx of auxin. The researchers genetically modified
root cells to lack plasmodesmata and exposed the root cells to auxin; the
roots did not grow. Therefore, they concluded that auxin must travel
through plasmodesmata to allow for root tip growth.
7. During the wound healing process, cells in the damaged area release the
growth factor EGF. EGF signals to surrounding cells to grow,
proliferate, and differentiate.
➔ Questions?
➔ Textbook
chapters/pages
to review
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Think, Pair, Share
How do you think cells process signals? Write your ideas down in the space below.
Cell Signaling:Overview
Cell-to-cell messages can be divided into three stages:
1.
2.
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3.
On the following pages these stages will be covered in more detail
➔ Questions?
➔ Textbook
chapters/pages
to review
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Stage 1: Reception
Reception:
Receptor:
●
All receptors have an area that ____________________ with the ligand and an area that
_________________ a signal to another protein
○
Binding between ________________ and _________________________ is highly
__________________.
When the ligand binds to the receptor, the receptor ___________________________ (via a
__________________________ change).
Allows the receptor to:
Initiates ____________________________________________
Receptors can be in the ____________________________________________ or
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________________________________.
➔ Questions?
➔ Textbook
chapters/pages
to review
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Plasma Membrane Receptors
Intracellular Receptors
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Note: the AP exam will not expect you to be able to classify any given
molecule as hydrophobic, usually they will either tell you it is
hydrophobic, or they will say the molecule is a steroid hormone.
➔ Questions?
➔ Textbook
chapters/pages
to review
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Stage 2: Transduction
Transduction:
Requires:
The signal transduction pathway regulates _________________ activity through:
*Remember: a change in
shape means
During transduction the signal is _______________________________.
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Second messengers:
➔ Questions?
➔ Textbook
chapters/pages
to review
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Stage 3: Response
Response:
Examples:
A.
B.
C.
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Quick Review
1.
What are the three stages of cell signaling?
2.
What is the actual “signal” being transduced in a signal transduction pathway?
3.
How is this “signal” passed from outside to inside the cell?
➔ Questions?
➔ Textbook
chapters/pages
to review
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Signal Transduction Pathways
Signal transduction pathways can influence:
They can result in changes in:
Changes in Signal Transduction Pathways
Practice FRQ
Some diseases, such as cancer or diabetes, are caused by defective protein phosphatases. Explain how such a
defective protein would affect a signal transduction pathway.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
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_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
➔ Questions?
➔ Textbook
chapters/pages
to review
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Review: Cell Communication
1. What are the three main ways that cells communicate?
2. Classify the images below by their type of communication
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3. Ligand-receptor binding is highly specific. What does this mean?
4. Compare direct contact communication in animal cells and plant cells.
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5. Label the 3 stages of signal transduction using the image below.
6. In the first stage of cell signaling, a _______________ binds to a __________________, which can
either be in the plasma membrane or ____________________.
7. In the second stage of cell signaling, the signal is converted and it will bring about a ______________
________________.
8.
Differentiate between the roles of protein kinases and protein phosphatases in the second stage of
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signaling pathways.
9.
In the third stage of cell signaling, the final molecule in the signaling pathway will convert the signal
to a response that will alter a(n) __________________ ______________________.
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Important Receptors
In eukaryotic organisms there are two main categories of cell membrane receptors:
1.
2.
GPCRs
G protein coupled receptors (GPCRs):
The GPCR, enzyme, and G protein are inactive until ligand binding to GPCR on the extracellular side
Ligand binding causes ______________________ side to change shape
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Part of the activated G protein can then bind to the enzyme.
➔ Questions?
➔ Textbook
chapters/pages
to review
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Ion Channels
Ligand gated ion channels:
Located:
Important in the:
Receptors that act as a __________________ for ions
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➔ Use this space to reflect on topics 1, 2, 3, and 4
➔ Textbook chapters/pages to review
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The Secret Life of Plants
Look at the picture of the potted house plant to the right. What do you think when you see it?
Do you think that this plant can express itself? Can it communicate with other species?
Now look at the picture of the tree to the left. Do you think the tree
understands its surroundings? Can it communicate with nearby trees if
there is danger? Well, it turns out that all the above are true! Most people don’t realize that
plants have fine-tuned mechanisms of communication, and it turns out scientists didn’t know
either until only recently! Two studies published in 1983 demonstrated that willow trees, poplars, and sugar maples
can warn each other about insect attacks. Scientists found that intact, undamaged trees near ones that are infested
with hungry bugs begin pumping out bug-repelling chemicals to ward off attack. In 2006, studies done on plants
found that they have a two branched innate immune system to protect themselves from bacterial, viral, and fungal
infections. So how do exactly can plants do this? Well, they use signaling cascades!
A Call for Nutrients
Trees, like redwoods, can grow to be massive structures reaching over 300 feet in height! A forest full of these
skyscraper trees would naturally draw your attention upwards toward the sky to marvel
at their beauty. But it turns out that there are even more massive and complex structures
under your own feet! Most people know that the roots of trees extend deep into the ground,
where they take up nutrients and water, but there is also a full network of fungal fibers
underneath the soil that interact with the roots of trees. These fungal fibers are known as
mycorrhizal networks. Mycorrhizal networks are so immense and complex in forest biomes
that they have been dubbed “The Wood Wide Web.” These fungal networks have a
symbiotic relationship with 80% of all plants. In forest biomes, the fungi take about 30% of the sugar the trees
produce by photosynthesis for their own use. In exchange the fungus grows and spreads deep into the surrounding soil
to find nutrients and water, which it then pumps to trees in need. So, what does a new tree (sapling) do in order to gain
access to this fungal network? The sapling releases strigolactones. Strigolactone is a hormone that can be recognized
by mycorrhizal fungi in the soil and allows the fungi to “detect” the host plant. When the mycorrhizal fungi receives
the strigolactones, it creates a signaling cascade that results in fungal growth. This pathway can be seen in Figure 1.
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Use Figure 1 to answer questions 1-4.
Fig. 1 Strigolactone Signaling in Fungal Cells
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1. On Figure 1, label the three stages of cell signaling.
2. Classify strigolactone as polar (hydrophilic) or non-polar (hydrophobic). How can you tell by examining Fig. 1?
3. How are messages relayed in cells? How are they amplified?
4. What is the fungal cell’s response to the message received?
A Warning Signal
Besides communicating through fungal networks, plants can also communicate by releasing chemicals in the air. The
thorn acacia in sub-Saharan Africa is an excellent example of how plants can warn other nearby
plants of threats. When a giraffe begins to chew acacia leaves, the tree notices the injury and
emits a distress signal in the form of ethylene gas. This gas is released into the air and can
travel up to 50 yards. Upon detecting this gas, neighboring acacias start releasing tannins into
their leaves. In large enough quantities tannins can sicken or even kill large herbivores.
Giraffes are one such herbivore that commonly feed on acacia trees. So how are giraffes able
to eat the acacia tree leaves? Giraffes can detect ethylene gas in the air, which is why
when giraffes feed on the acacia tree they do so into the wind, so the warning gas doesn’t reach the trees ahead of
them. If there’s no wind, a giraffe will typically walk 100 yards— farther than ethylene gas can travel in still
air—before feeding on the next acacia. The figure below represents ethylene signaling in acacia trees.
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Use Figure 2 to answer questions 5-10
Fig. 2 Communication Via Ethylene Gas
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5. Where is the receptor located that binds to ethylene?
6. Before the acacia tree receives ethylene, is it producing tannins? Why or why not?
7. When ethylene binds to the receptor, what happens to the repressor bound to the transcription factor?
8. What happens to the transcription factor? What does this allow for?
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9. What is being produced inside the cell now?
10. How is what is being produced leaving the cell?
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