Cell Communication and Signaling

Study Notes

Cell Communication

Multicellular organisms maintain homeostasis by cells constantly communicating with each other.
Many mechanisms exist for transmitting information between cells, tissues, and organs, including electrical and chemical signaling.
Organisms communicate with members of their species by secreting chemical signals (e.g., bacteria release chemical signals that diffuse, and concentration increases with population).

Cell Signaling

Refers to the mechanisms by which cells communicate with each other.
Cell signaling is a part of a complex system that regulates cellular activities and coordinates cell actions.
Cellular response to microenvironment is vital for development, tissue repair, immunity, and homeostasis.
Errors in information processing contribute to diseases like cancer, autoimmunity, and diabetes. Understanding cell signaling can lead to effective disease treatment.

Learning Objective 1

What sequence of events takes place during cell signaling?

Cell Signaling - Steps

1. Synthesis, release, and transport of signaling molecules:
- Neurotransmitters, hormones, are examples of signaling molecules.
- Ligand: An ion, molecule, or group that binds another entity to create a larger complex.
2. Reception of information by target cells:
- Target cells are capable of responding to specific signals.
3. Signal transduction:
- The process of a cell converting an extracellular signal into an intracellular signal to cause changes in the cell.
4. Response by the cell:
- Example: insulin stimulates cells to absorb glucose from the blood, lowering blood glucose levels.

Cell Signaling (Diagram Explanation)

Reception: Signaling molecules bind to receptors (large proteins or glycoproteins).
Signal transduction: A series of molecular interactions causes a change in the cell.
Response: Altered metabolism, altered membrane permeability, or altered gene activity.

Key Concepts

Cells use chemical compounds (neurotransmitters, hormones, and other regulatory molecules) to communicate with each other.

Learning Objective 2

Describe three types of signaling molecules.

Signaling Molecules

Local regulators
Neurotransmitters
Hormones

Local Regulators

Paracrine regulation: Signals diffuse through interstitial fluid, act on nearby cells.
Examples:
- Histamine (allergic reactions)
- Growth factors (cell division)
- Prostaglandins (modifies cAMP and stimulates smooth muscle contraction)
- Nitric Oxide (relaxes smooth muscles in blood vessels)

Neurotransmitters

Chemical signals released by neurons (nerve cells).
Neurons transmit signals across synapses.

Hormones

Chemical messengers in plants and animals.
Secreted by endocrine glands in animals.
Transported by blood to target cells.

Learning Objective 3: Receptor Specificity

What mechanisms make reception a highly specific process?

Receptors

Large proteins or glycoproteins that bind with signaling molecules.
Ligand: A signaling molecule that binds to a specific receptor.
Receptors have specific shapes; only matching signaling molecules affect a specific cell. Different cells have different receptors. The same cell can produce different receptors at different stages or under different conditions.

Receptors (Hydrophilic vs. Hydrophobic Ligands)

Hydrophilic (water-soluble) signaling molecules: Cannot pass through the plasma membrane. They bind to receptors on the cell surface.
Hydrophobic (lipid-soluble) signaling molecules: Pass through the plasma membrane and bind with receptors in the cytosol or nucleus.

Learning Objectives 4 & 5: Receptor Types

Compare: ion channel-linked receptors, G protein-linked receptors, enzyme-linked receptors, and intracellular receptors.

Ion Channel-Linked Receptor

Signaling molecule binds to an ion channel-linked receptor, and the ion channel opens or closes.
Converted chemical signals into electrical signals. Channels remain closed until ligands bind.

G Protein-Linked Receptor

Transmembrane proteins that couple signal molecules to signal transduction pathways.
The receptor has a tail extending into the cytosol and a binding site for a G protein (which binds to GTP).

G Protein-Linked Receptors (Continued)

Large family of transmembrane proteins.
Loops back and forth through the plasma membrane (7 times).
Receptor made of seven transmembrane alpha helices connected by loops.
Ligand binds with receptor; guanosine diphosphate (GDP) released; replaced by GTP.
Activated G protein initiates signal transduction; activates enzymes and changes cell function.

Enzyme-Linked Receptor

Functions directly as enzymes or linked to enzymes.
Transmembrane proteins; binding site outside (for signaling molecules) and binding site inside (for enzymes).
One major group is tyrosine kinases (tyrosine is an amino acid).
Tyrosine kinase receptors bind signaling molecules, which causes them to come together, thus activating tyrosine kinase and phosphorylation of neighboring receptors.

Intracellular Receptor

Located in the cytosol or nucleus.
Ligands are small, hydrophobic molecules that diffuse across the plasma membrane.
Steroid hormones combine with intracellular nuclear receptors, acting as transcription factors that activate or repress specific genes.

Cells Regulate Reception

By increasing or decreasing the number of receptors (synthesized or degraded) based on cell needs.
Receptor down-regulation: Hormone concentration is too high, so cells decrease insulin receptors
Receptor up-regulation: Response to low hormone concentration; cells synthesize more receptors, increasing signaling effectiveness.

Key Concepts (Signal Transduction)

In signal transduction, a receptor molecule converts an extracellular signal into an intracellular signal, causing changes in the cell.

Description

Explore the mechanisms of cell communication and signaling essential for maintaining homeostasis in multicellular organisms. This quiz covers the processes by which cells transmit information, how errors can lead to diseases, and the significance of cellular responses. Test your knowledge on the intricate systems that facilitate cellular interactions.

Cell Communication and Signaling

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Questions and Answers

What is the first step in the cell signaling process?

What is the role of local regulators in cell signaling?

What defines the role of a ligand in cell signaling?

Which process follows the reception of information by target cells?

Which statement about neurotransmitters is true?

What can result from errors in cellular information processing?

Which signaling molecule is NOT typically classified as a hormone?

How do hormones achieve their target effects in the body?

How does insulin affect blood glucose levels?

In cell signaling, what ensures the specificity of the reception process?