Bio presentation

1ST presenter – OVERVIEW OF CELL-SIGNALING

1. What is cell signaling? Define – importance

2. Picture of overall process of cell signaling. i.e. the one above
3. Components involved in the process what they are. For example, receptors are mostly protein-
ligands maybe ions or others.
4. Explain the overall mechanism – the three stages. Note that my colleagues will go in detail I will
only briefly explain the overall mechanism.
5. Types of cell signaling- associated with real life examples
6. Clinical correlation- mention and list diseases that result from a disorder or malfunction of cell
signaling.

Introduction: hi everyone good morning so we will be presenting on cell signaling, how this process is
carried out and the components basically ligand which are signaling molecules/ messengers they can be
proteins and peptides, lipids, ions –calcium ions, or even small molecules like adrenaline. Then we have
the receptors which are proteins or would just call them protein receptors and the possible health issues
associated with a disorder or malfunction in cell signaling essentially its health correlation.
I will define what cell signaling, state its importance
I will give the brief overview of its mechanism- which is a three step process and the types of cell
signaling and a few real life examples of cell signaling in action.
Define cell signaling-
Brief over view of the three stages of cell signaling
Types of cell signaling -Download animation of types of cell signaling-

Types of Cell Signaling

 Explain the different types of cell signaling with examples:

o Autocrine Signaling: The cell releases a signal that acts on itself.
 Example: Growth factors that promote cell division.
o Paracrine Signaling: The signal acts on nearby cells.
 Example: Neurotransmitters in synaptic signaling.
o Endocrine Signaling: The signal (usually a hormone) travels through the
bloodstream to distant cells.
 Example: Insulin regulating blood sugar levels.
o Juxtacrine Signaling: The signal requires direct contact between neighboring
cells.
 Example: Immune cells interacting with infected cells
What is cell signaling?

Cell signaling is a complex process due to the numerous signals, overlapping pathways, and
sometimes competing events happening simultaneously. A small set of extracellular signals can
mediate a wide range of cellular behaviors. How a cell responds depends on the genes being
expressed at a given time. For example, the signal acetylcholine can:

 Promote muscle contraction at neuromuscular junctions.

 Lower heart rate in cardiac pacemaker cells.
 Increase saliva production in salivary glands.

These different effects result from variations in release modes, receptor types, and internal
pathway components. This topic focuses on understanding the principles of cell signaling, with
examples of mechanisms to come later, helping you interpret signaling pathways effectively.

Components of cell signaling.

1. Ligands

 These are the signaling molecules that initiate communication. Examples include
hormones, neurotransmitters, and growth factors.
 They can be proteins, peptides, small molecules, or even gases like nitric oxide.
 Ligands bind to specific receptors to trigger a signaling event.

2. Receptors

 Located on the cell surface or inside the cell, receptors are highly specific to their ligands.
 Types of receptors:
o Cell-surface receptors: Found on the plasma membrane; they bind to hydrophilic
ligands that cannot cross the membrane (e.g., G-protein-coupled receptors,
receptor tyrosine kinases).
o Intracellular receptors: Found within the cytoplasm or nucleus; they bind to
hydrophobic ligands like steroid hormones that can cross the membrane.
3. Signaling Pathway Components

 Second Messengers: Small molecules like cAMP, calcium ions, or inositol triphosphate
(IP3) that relay and amplify the signal inside the cell.
 Signaling Proteins: These include:
o Kinases (enzymes that add phosphate groups to proteins to activate or deactivate
them).
o Phosphatases (enzymes that remove phosphate groups).
o Adapters and scaffold proteins that organize and relay signals.

4. Effector Proteins

 These are the final players in the signaling pathway that directly mediate the cellular
response.
 Examples:
o Transcription factors that regulate gene expression.
o Cytoskeletal proteins that control cell shape or movement.
o Enzymes that drive metabolic changes.

5. Feedback Mechanisms

 Positive feedback amplifies the signaling response.

 Negative feedback dampens or terminates the signal to maintain balance and prevent over
activation.

When I say "trigger the start of the signaling cascade," I mean that the receptor, upon binding to
the ligand (signaling molecule), activates a series of events inside the cell. This series of events is
often referred to as a "cascade" because it involves multiple steps, where each step activates the
next, amplifying and transmitting the signal through the cell.

Here's how it works:

1. Ligand Binding: A ligand (e.g., hormone, neurotransmitter) binds to its specific

receptor, either on the cell surface or inside the cell.
2. Receptor Activation: The receptor undergoes a change—such as a structural or chemical
modification—that "turns it on."
3. Signal Transmission: The activated receptor interacts with intracellular signaling
molecules like kinases or second messengers, passing the signal deeper into the cell.
4. Amplification: At each step, the signal is often amplified, meaning a single ligand can
lead to a large-scale cellular response.
5. Effector Activation: The final components (effector proteins) are activated to carry out
the cell's response, like gene expression, movement, or metabolism changes.
 In short, "triggering the cascade" refers to the process of initiating this chain reaction, starting
with ligand-receptor interaction, that ultimately leads to a specific cellular outcome. Let me
know if you'd like a specific example!

Cell signaling process

1. A signal is sent. There are a number of ways this could happen. A cell could release a
molecular cue, or the environmental conditions themselves could provide the
molecule that is being detected. We’ll do a more in-depth exploration of signals and
ligands shortly.
2. This signal is received by the cell. This will require a receptor to recognize the signal
and respond to it. Most often the receptor is at the cell surface, since that’s where
signals would arrive first, but it doesn’t have to be. Nitric oxide (NO) is an example of
a signaling molecule that can diffuse across cell membranes, so its receptor is in the
interior of the cell.
3. The signal is “interpreted” by the cell that receives it. This could involve a number of
things, like splitting the signal so that multiple responses are possible; it also likely
involves transferring the signal across the plasma membrane by activating specific
internal responses. This interpretation step is called transduction.
4. Finally, the cell responds to the signal. A cell could have multiple responses to a
signal. Some responses are fast, while others are slow. If the signal is used to start a
process, like cell division, apoptosis, or changes in cell identity, then there could be
multiple changes in the cell as it prepares for the new behavior.

Slide 1: Overview of Cell Signaling

 Purpose: Cell signaling allows cells to detect and respond to their environment.
 Key Components:
o Ligands: Signaling molecules that bind to receptors (e.g., hormones,
neurotransmitters).
o Receptors: Proteins that detect ligands; located on the cell surface, cytoplasm, or
nucleus.
o Signal Transduction Pathway: Amplifies the signal through intracellular events.
o Effector Proteins: Trigger the final cellular response.

Slide 2: Types of Cell Signaling

1. Endocrine Signaling (Long-Distance)

 Hormones travel via the bloodstream to target cells far away.

 Speed: Slow (minutes).
 Receptor Sensitivity: High affinity to detect dilute ligands.
 Examples: Insulin, adrenaline, estrogen.

2. Neuronal Signaling (Long-Distance)

 Electrochemical signals travel through neurons.

 Speed: Fast (milliseconds).
 Process:
o Signals stay within nerve cells for rapid transmission.
o Neurotransmitters (e.g., dopamine, acetylcholine) transfer signals to target cells.
 Receptor Sensitivity: Low affinity as neurotransmitters flood the synapse.

Slide 3: Medium- to Short-Distance Signaling

3. Paracrine Signaling

 Local signaling; ligands diffuse through the extracellular matrix to nearby cells.
 Response: Dose/gradient-dependent; allows varied responses.
 Examples: Synaptic signaling, growth hormones during development.

4. Autocrine Signaling

 Self-signaling; a cell releases ligands that bind to its own receptors.

 Functions:
o Amplifies immune response.
o Promotes unregulated growth in cancer cells.
 Dual Action: May affect the releasing cell and neighboring cells.

Developmental Differentiation:

 During early development, once a cell starts differentiating into a specific type, it secretes
autocrine signals.
 These signals bind back to its own receptors to reinforce its developmental decision,
ensuring it stays committed to that specialized path.
 When neighboring identical cells also release and receive these autocrine signals
simultaneously, they collectively reinforce each other's differentiation path.
 This creates a community effect, where a group of identical cells synchronously adopt
the same developmental fate. For instance, a group of embryonic stem cells might
differentiate into nerve cells by sharing and responding to the same autocrine signals.
However, a single isolated cell might not respond in this way without the group support.

2. Role of Eicosanoids in Mature Mammals:

  Eicosanoids, such as prostaglandins, are a class of signaling molecules that act in an
autocrine mode.
 They are continuously synthesized in the plasma membrane and released into the
extracellular environment.
 Their main function includes regulating pain, inflammation, and immune responses. For
example:
o Prostaglandins produced by immune cells can signal the same cells to modulate
inflammation at the site of infection.
 These molecules are rapidly degraded by extracellular enzymes, ensuring they act locally
and do not spread far, maintaining tight control over their effects.

Both examples highlight how autocrine signaling plays critical roles in developmental biology
and immune system regulation by enabling cells to communicate with themselves and their
neighbors effectively.

5. Juxtacrine Signaling (Contact-Dependent)

 Direct communication via cell-to-cell contact or extracellular matrix interaction.

 Examples:
o Integrins: Bind to the matrix, preventing apoptosis.
o Notch-Delta Signaling: Critical for cell fate during embryonic development.

1. Juxtacrine Signaling: Notch-Delta Signaling

 Mechanism: Juxtacrine signaling requires direct physical contact between adjacent

cells. The signaling molecule is not secreted but remains attached to the surface of the
signaling cell, while the receptor is present on the surface of the neighboring target cell.
 Example - Notch-Delta Signaling:
o Role in Development: During embryonic development, cells use this pathway to
determine their fate. The Notch receptor on one cell interacts with the Delta
ligand on a neighboring cell, triggering changes in gene expression that define the
cell's developmental trajectory (e.g., becoming a neuron or glial cell).
o Specificity: This signaling ensures a precise and localized response because only
neighboring cells in direct contact are affected.
o Community Effect: Juxtacrine signaling like Notch-Delta maintains cellular
coordination, preventing isolated cells from differentiating improperly.

2. Gap Junction Signaling: Coordination in Heart Muscle Cells

 Mechanism: Gap junction signaling involves the formation of specialized protein

channels called gap junctions that physically connect the cytoplasm of neighboring cells.
 Example - Heart Muscle Cells:
o Synchronization: In cardiac muscle tissue, gap junctions allow the direct
exchange of ions, such as calcium and potassium, between adjacent cells. This
 facilitates the rapid transmission of electrical signals, enabling the heart muscle
cells to contract in a coordinated rhythm (essential for pumping blood efficiently).
o Precision: Gap junctions ensure that only connected cells respond together,
producing a unified contraction across the heart muscle.

Comparison of Both Examples

 Juxtacrine signaling emphasizes cell-specific interactions through direct contact for

differentiation, while gap junction signaling enables rapid communication between
physically connected cells for functional coordination (e.g., muscle contraction).

Slide Title: Endocrine Signaling

 Definition: Specialized endocrine cells release hormones.

 Transport Mechanism: Hormones travel through bodily fluids like blood (in animals) or
sap (in plants) to reach distant target cells.
 Key Characteristics:
o Wide Range: Signals can reach cells distributed throughout the organism.
o Slow Process: Relies on diffusion and fluid circulation, making it slower than
other signaling types.
 Examples: Regulation of blood sugar by insulin (animals); growth control via auxins
(plants).

 In response to stress, the adrenal glands release cortisol, a hormone that travels through
the bloodstream to various parts of the body. Cortisol binds to receptors in cells of the
liver, muscles, and fat tissues to trigger responses like:

 Increasing glucose production for energy.

 Breaking down fat and protein for fuel.
 Suppressing non-essential functions, like the immune response, to prioritize survival.

How It Happens:

Nerve cells (neurons) transmit electrical signals called action potentials. When a neuron is
stimulated, an electrical impulse travels down its axon toward the synapse (a gap between two
neurons). At the synapse, this signal triggers the release of chemical messengers called
neurotransmitters, which cross the synaptic gap and bind to receptors on the neighboring
neuron, continuing the signal.

Key Characteristics:

1. Speed and Precision: Electrical impulses can travel at speeds up to 100 m/s, ensuring
rapid communication.
 2. Unidirectional: Signals only flow from the sending neuron (presynaptic) to the receiving
neuron (postsynaptic).
3. Specificity: Only certain neurotransmitters bind to specific receptors, ensuring precise
messaging.
4. Short-Range: Synaptic signaling occurs over very small gaps, typically about 20
nanometers wide.

Examples:

 Reflex Actions: When you accidentally touch something hot, sensory neurons rapidly
signal the spinal cord, and motor neurons trigger a reflex to pull your hand away.
 Muscle Contraction: Neurotransmitter acetylcholine is released at the synapse between
motor neurons and muscle cells, leading to muscle contraction.
 Memory Formation: Synapses in the brain strengthen or weaken based on activity,
enabling learning and memory (a process called synaptic plasticity)

Title: Nerve Cells and Synaptic Signaling

 Specialized Cells: Neurons are specialized cells designed for signaling. They can
transmit information across the body by extending long processes (axons) that physically
reach distant target cells. This allows communication between parts of the body that are
far apart.
 How It Happens:
o Signals are transmitted via electrical impulses (action potentials) within the
nerve cells.
o These impulses travel down the axon to nerve terminals.
o At the terminal, neurotransmitters are released into the synapse.
o Neurotransmitters cross the short synaptic gap (~20 nm) and bind to receptors on
the target cell.
 Key Point: While the axons allow neurons to send signals over long distances, the final
signal transfer at the synapse is a short-range, highly targeted interaction.
 Key Features:
o Speed: Up to 100 m/s
o Unidirectional and specific signaling
o Short-range, precise communication
 Examples: Reflex actions, muscle contraction, memory formation.

The second characteristic of paracrine signaling ensures that signaling molecules are delivered
only to nearby target cells without spreading too far or affecting unintended areas. This is
achieved through the following mechanisms:

1. Rapid Uptake by Target Cells:

o Neighboring cells quickly absorb the signaling molecules, preventing them from
spreading beyond the intended local area.
o This ensures a focused and efficient response from specific target cells.
2. Destruction by Extracellular Enzymes:
 o Enzymes in the extracellular space break down the signaling molecules shortly
after their release.
o This limits the distance the signal can travel and prevents it from lingering in the
environment.

Together, these mechanisms maintain the localized action of paracrine signaling, making it
precise and effective for processes like immune responses, tissue repair, and embryonic
development

The second characteristic of paracrine signaling ensures that signaling molecules are delivered
only to nearby target cells without spreading too far or affecting unintended areas. This is
achieved through the following mechanisms:

1. Rapid Uptake by Target Cells:

o Neighboring cells quickly absorb the signaling molecules, preventing them from
spreading beyond the intended local area.
o This ensures a focused and efficient response from specific target cells.
2. Destruction by Extracellular Enzymes:
o Enzymes in the extracellular space break down the signaling molecules shortly
after their release.
o This limits the distance the signal can travel and prevents it from lingering in the
environment.

Together, these mechanisms maintain the localized action of paracrine signaling, making it
precise and effective for processes like immune responses, tissue repair, and embryonic
development. Let me know if you'd like further examples or clarifications!

In paracrine signaling, molecules are rapidly absorbed by nearby cells or broken down by
extracellular enzymes to ensure the signal stays localized and doesn't spread too far.

"Localized by rapid uptake/destruction."

localized as in?

In the context of paracrine signaling, localized refers to the fact that signaling molecules act only
on nearby target cells rather than spreading to distant cells. This localization is ensured by
mechanisms like rapid uptake of the molecules by neighboring cells or their destruction by
extracellular enzymes. Essentially, it keeps the signal confined to a specific area. Let me know if
you'd like further elaboration!

explain the examples

Here’s a detailed explanation of the examples mentioned for paracrine signaling:

1. Synaptic Signaling in Neurons:

 In this process, neurotransmitters (chemical signals) are released by a nerve cell
o
(neuron) into the small gap called the synapse.
o These neurotransmitters diffuse across the synapse and bind to receptors on the
nearby target cell, such as another neuron or a muscle cell.
o This localized action is critical for fast and precise communication in the nervous
system, such as transmitting signals to control muscle movement or relay sensory
information.
2. Chemokine Release by Neutrophils:
o Neutrophils, a type of white blood cell, release chemokines (specialized signaling
molecules) during an immune response.
o These chemokines attract and activate nearby immune cells, such as other
neutrophils or macrophages, to help fight infection or heal tissue.
o This local and targeted response ensures the immune reaction is focused on the
area of infection or injury, preventing unnecessary effects on distant cells.

Both examples highlight how paracrine signaling allows localized and efficient communication
between cells in specific scenarios, whether in the nervous system or during an immune response