AP BIO CELL SIGNALING

What is cell communication?

Cells send, receive, and respond to information about their environment to maintain survival and respond to changes.

What are ligands?

Chemical signaling molecules that bind to specific receptors on or inside target cells. Examples include proteins, cholesterol, and ions.

What is autocrine signaling?

A cell releases a ligand that binds to a receptor on the same cell, triggering a response within itself. Auto = self.

What is an example of autocrine signaling?

Cancer cells release their own growth signals (ligands), stimulating themselves to grow and divide.

What is juxtacrine signaling?

Signaling that requires direct contact between the cell sending the ligand and the receiving cell. The ligand binds to a receptor on the neighboring cell.

What are examples of juxtacrine signaling?

Plasmodesmata in plants allow signaling between adjacent cells. Antigen-presenting cells communicate with T cells through direct cell-to-cell contact.

What is paracrine signaling?

A cell releases ligands that travel a short distance, affecting nearby cells. These ligands are called local regulators.

What is an example of paracrine signaling?

Neurotransmitters travel across a synapse to communicate with nearby cells

What is endocrine signaling?

Signaling in which ligands travel long distances between cells, often through the bloodstream. These ligands are called hormones.

What are examples of endocrine signaling?

Insulin travels through the bloodstream from the pancreas to body cells. Ethylene travels through the air to trigger fruit ripening.

What is signal transduction?

The process that determines how a cell responds internally to an environmental signal. It can affect gene expression, cell growth, cell division, and hormone release.

What happens when a ligand binds to a target cell?

It interacts with a specific receptor, triggering signal transduction and eventually producing a cellular response.

What are hydrophilic ligands?

Water-loving ligands that cannot cross the phospholipid bilayer. They bind to receptors on the cell membrane.

What happens after a hydrophilic ligand binds to its receptor?

The membrane receptor triggers a series of chemical reactions inside the cell, leading to a response.

What are hydrophobic ligands?

Water-fearing ligands that can cross the phospholipid bilayer and enter the cell. They bind to intracellular receptors in the cytosol.

What happens after a hydrophobic ligand binds to its receptor?

The ligand-receptor complex can cross the nuclear membrane and bind to DNA, changing gene expression

What are the three major steps of signal transduction?

Reception

Transduction

Response

What happens during reception?

A ligand binds to a specific receptor on the cell membrane or inside the cell. This causes a conformational (shape) change that triggers the next step.

Why can't a cell respond to every ligand?

Receptors have ligand-specific binding domains. Without the correct receptor for a ligand, the cell cannot respond to that signal.

What are two examples of receptors?

G-protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs).

What happens during transduction?

A series of chemical reactions triggered by ligand-receptor binding. These reactions help the cell choose the appropriate response.

What are signaling cascades and signal amplification?

Signaling cascades are chains of chemical reactions. Signal amplification occurs when one molecule activates multiple molecules, increasing the cell's response.

What are kinases and phosphatases?

Kinases transfer phosphate groups to other molecules, activating them. Phosphatases remove phosphate groups, inactivating them.

What are secondary messengers? Give an example.

Small molecules that relay signals inside the cell. Example: cAMP, produced from ATP by the enzyme adenylyl cyclase.

What happens during the response step?

The final step of signal transduction. The cell produces a response, such as gene activation, opening ligand-gated ion channels, or initiating apoptosis (programmed cell death).

How can mutations in receptor genes disrupt signaling?

A mutation can change a receptor's shape so it cannot bind its specific ligand. Without a functional receptor, the cell cannot respond.

What are androgen insensitivity syndrome (AIS) and nephrogenic diabetes insipidus (NDI)?

AIS: Nonfunctional testosterone receptors affect embryonic gonadal development. NDI: Kidney cells cannot properly respond to ADH, affecting urine production

How can environmental molecules disrupt signal transduction?

They can interfere with ligand-receptor binding. Example: Cholera toxin binds to GPCRs, disrupting signaling and potentially causing life-threatening dehydration.

How can a mutation in adenylyl cyclase affect signaling?

It can prevent proper production of the secondary messenger cAMP, disrupting all later steps that depend on cAMP.

What are negative and positive feedback?

Negative feedback reverses a change and returns a system toward homeostasis. Positive feedback amplifies a process until a particular result is achieved.

Give examples of negative and positive feedback.

Negative: Sweating cools the body; insulin lowers high blood glucose; glucagon raises low blood glucose.

Positive: Oxytocin increases uterine contractions, triggering more oxytocin during childbirth.